Séminaire Temps/Fréquence du SYRTE

18 juillet 2019

**Séminaire organisé par :**

Sébastien Merlet (SYRTE)

Courriel - Tél. : +33 (0) 1 40 51 23 93

**Lieu :**

Le jeudi à 11h

Salle de l’Atelier

Observatoire de Paris

77, Avenue Denfert-Rochereau

75014, Paris.

### Prochain séminaire :

24 octobre 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Table-top cosmology with quantum sensors

Andrei Derevianko

University of Nevada - Reno, USA

Laboratory cosmology is a nascent field offering an intriguing potential for exacting the nature of dark matter and dark energy with small-scale experiments. The searches involve precision sensors and rely on detecting predicted dark sector signatures. I will review such signatures with an emphasis on atomic clocks, atom interferometers, and their networks. I will illustrate these ideas using our dark matter search with atomic clocks on board Global Positioning System satellites.

### Saison 2019-2020 :

5 septembre 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Demonstration of non-exponential quantum decoherence and non-monotonic quantum diffusion in a Lévy kicked rotor system.

Sumit Sakar

IISER - India

In general, quantum systems lose decoherence exponentially fast upon interacting with the environment, and this puts a limitation on some technological applications (e.g. quantum information processing, where larger gate operation time is needed) using such quantum systems. In this talk, I will present our work where we use an atom-optics delta kicked rotor subjected to non-stationary Lévy noise in the kicking sequence and demonstrate slower than exponential decoherence manifested in the form of sub-diffusion in the mean energy growth of the rotor. We observed that in a particular regime of the noise, the system displays non-monotonic quantum diffusion, where the optimal diffusion rate can be tuned by right choices of the parameters characterization the system and the strength of the noise. Such non-monotonic diffusion are not reported in case of a standard quantum kicked rotor and will be helpful in understanding quantum transport in kicked rotor.
A part of this work has been published in Phys. Rev. Lett. 118, 174101 (2017).

12 septembre 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Orientations R&D de la Défense en matière de Guidage Navigation

Marina Ballanger

DGA

19 septembre 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Shelving spectroscopy of the strontium intercombination line

Martin Robert de Saint Vincent

LPL

I will present a spectroscopy scheme for the 7-kHz wide 689 nm intercombination line of strontium. It is based on shelving detection, where the atoms are first excited to a metastable state by the spectroscopy laser, before their state is probed using the 30-MHz broad transition at 461 nm. This enhances dramatically the signal strength as compared to direct saturation spectroscopy of the narrow line, which remains the most used method for the intercombination line of strontium. Our approach is comparable to thermal beam Calcium clocks, that gained more than one order of magnitude in precision when implementing shelving detection. The signal enhancement eliminates the need for high strontium density, increasing source lifetimes, and reduces the requirements on the detection. We demonstrate shelving spectroscopy both in a directed thermal beam and in a hot vapour cell, showing that the scheme can be easily implemented in most existing strontium experiments. Shelving spectroscopy of strontium may also be of interest for transportable optical clocks, given the possibility of low complexity, high compactness, long lifetimes and low (400°C) oven temperatures.
This work was implemented as spectroscopy for two new quantum gas experiments, at Laboratoire de Physique des Lasers and Laboratoire Charles Fabry. I will take this opportunity to briefly introduce the new large spin Fermi gas of 87Sr at LPL and its first steps in the degenerate regime.

26 septembre 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Cold-Atom Gravimetry and Spin Related Equivalence Principle Test at HUST

Xiaobing Deng

CGE HUST China

In the past two decades, cold-atom interferometry has been instrumental in both precise gravity measurements and fundamental physics tests. In this talk, I will present research work along these lines performed at HUST (Huazhong University of Science and Technology). I will first present the realization of ultrahigh sensitivity atom gravimeters. An atomic fountain based absolute gravimeter with a sensitivity of 4.2 µGal/Hz^1/2 was demonstrated, thanks to the drastic suppression of the vibration noise. Later, a transportable gravimeter with an accuracy of 3 µGal was built, which participated to the 10th International Comparison of Absolute Gravimeters (ICAG). I will then discuss a direct test of the spin related universality of free fall, which we have performed using 87Rb atoms in opposite spin orientations, mF=+1 versus mF=?1. The resulting Eötvös ratio was measured to be ?S = (0.2±1.2) × 10^?7. This also gave an upper limit of 5.4×10^?6 m^?2 for the gradient of a possible spacetime torsion field. Further improvements of the test precision by using single internal state atom interferometers will be introduced.

17 octobre 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Aspects of Lorentz Violation in Gravity and Cosmology

Albin Nilsson

22 octobre 2019,
14h00

Danjon (Paris)

Ultra broadband, high power frequency combs

Martin Fermann

IMRA

Attention, salle, jour et horaire inhabituels

Fully coherent combs spanning more than two octaves are described for precision clock applications. High power combs enable supercontinuum compression to few cycle pulses at peak powers > 1 MW and offer new
opportunities in broadband mid IR spectroscopy and harmonic generation. In conjunction with OEO technology ultra-high stability tunable microwaves are demonstrated.

24 octobre 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Table-top cosmology with quantum sensors

Andrei Derevianko

University of Nevada - Reno, USA

Laboratory cosmology is a nascent field offering an intriguing potential for exacting the nature of dark matter and dark energy with small-scale experiments. The searches involve precision sensors and rely on detecting predicted dark sector signatures. I will review such signatures with an emphasis on atomic clocks, atom interferometers, and their networks. I will illustrate these ideas using our dark matter search with atomic clocks on board Global Positioning System satellites.

30 octobre 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Chris Oates

NIST

Attention jour inhabituel

7 novembre 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Towards optical manipulation of ytterbium Rydberg atoms: a study of auto-ionization

Patrick Cheinet

LAC

Cold atom experiments start using Rydberg atoms to perform quantum simulations. So far they use alkali atoms but new experiments aim at using alkali-earth. These atoms present the interesting opportunity to act on the second electron after exciting the first to a Rydberg level. It might allow efficient trapping and/or imaging of the Rydberg atoms. But during this excitation, the atom accesses to doubly excited states, above the first ionization limit, and can in principal ionize. We study this auto-ionization process and identify the possible optical manipulation techniques.

### Saison 2018-2019 :

13 septembre 2018,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Expériences récentes à Artemis + Geoazur/OCA : télémètre laser, stabilisation de fréquence laser, télécom optique

Duy-Hà Phung

SYRTE

Premièrement, je présenterai mon travail de thèse qui a consisté à concevoir et à mettre au point un télémètre laser permettant la mesure des distances absolues avec une exactitude nanométrique en utilisant un nouveau concept de mesure combinant une mesure interférométrique réalisée sur un faisceau à deux modes et une mesure de temps de vol. Afin qu'elles ne soient pas affectées par les dérives lentes de l'instrumentation microonde, les deux mesures de phase de longueur d’onde optique (1.55 µm) et de longueur d’onde synthétique (15 mm) sont extraites d'un même signal d’interférence à deux modes en utilisant un signal d’interférence à trois valeurs de la fréquence optique, calculées d'après le résultat de la mesure de temps de vol. Le montage expérimental a montré une résolution de 100 pm à 100 µs sur la mesure d’un chemin optique de 8 m dans l'air.
Deuxièmement, je vous présenterai le projet de raffinement et stabilisation de fréquence laser pour une diode laser commerciale. Un asservissement type Feed-back + Feed-Forward nous permet d'affiner la largeur spectrale de 2 MHz à 4 kHz, avec 99 % puissance optique du laser concentrée dans la bande de 150 kHz autour du pic central. La méthode Feed-back + Feed-Forward, avec un modulateur de phase - compensation de retard donnant une bande passante de plusieurs MHz sur l'asservissement.
Ensuite, je présenterai le projet "Contrôle <<µK de la température d'un résonateur fibré". Deux lasers sont verrouillés sur deux modes de polarisation d’une cavité fibrée. C’est grâce à la grande sensibilité thermique de la biréfringence de la fibre optique, qu’il est possible d’asservir les fréquences des lasers en stabilisant la température de la cavité. La température de la cavité est contrôlée finement en l'éclrairant par des LEDs, à moins de 70nK à l'échelle de la minute, et à moins de 500nK à l'échelle de la journée. Cette stabilité thermique laisse espérer une stabilité de fréquence relative de quelques 10^-13 aux temps courts (2 ou 3x10^-12 aux temps longs) pour les lasers stabilisés sur ce résonateur.
Enfin, je présenterai rapidement le projet de télécom optique en espace libre, DOMINO (Démonstrateur Optique pour les transMissions haut débIt eN Orbite). Les objectifs de ce projet sont d’établir des liens télécom optique expérimentaux entre la station au sol (OGS) MéO, localisée à Calern - Grasse, et divers satellites en orbite basse afin d’étudier la propagation laser lors de son passage à travers l’atmosphère et de proposer un design instrumental comportant les ingrédients fondamentaux des futurs segments sols.

20 septembre 2018,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Solving hard computational problems with coupled lasers

Nir Davidson

Weizmann Institute of Science

Hard computational problems may be solved by physics systems that can simulate them. Here we present a new a new system of coupled lasers in a modified degenerate cavity that is used to solve difficult computational tasks. The degenerate cavity possesses a huge number of degrees of freedom (> 300 000 modes in our system), that can be coupled and controlled with direct access to both the x-space and k-space components of the lasing mode. Placing constraints on these components can be mapped to different computational minimization problems. Due to mode competition, the lasers select the mode with minimal loss to find the solution. We demonstrate this ability for simulating XY spin systems and finding their ground state, for phase retrieval, for imaging through scattering medium and more.

25 septembre 2018,
14h00

Salle Danjon (Paris)

Chip-scale Atomic Devices: Miniature Precision Instruments using Atoms, Lasers and Silicon Micromachining

John Kitching

NIST

There is currently a strong movement worldwide toward portable, battery operated, wirelessly connected devices such as GPS receivers, cellular telephones and laptop computers and tablets. This new generation of electronics enables vast new capability, but also comes with new challenges such as bandwidth limitations, sensitivity to jamming and reduced access to calibration. A new generation of miniature, low-power, low-cost precision instruments is being developed at NIST for use in such portable technologies. These include clocks, magnetometers, gyros and wavelength references, all based on precision atomic spectroscopy and using emerging new fabrication capabilities such as microelectromechanical systems and photonics. This talk will describe the design, fabrication and performance of these instruments, as well as touch on several applications to which they are well-suited. Finally, we will speculate on future opportunities for these types of devices such as compact instruments based on laser-cooled atoms and a broader view on highly accurate chip-scale measurements.

5 octobre 2018,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Composite quantum systems at the interface with general relativity

Magdalena Zych

University of Queensland - Autralie

A major goal of modern physics is to understand and test the regime where quantum mechanics and general relativity both play a role. However, its new effects are thought to be relevant only at high energies or in strong gravitational fields, beyond the reach of present-day experiments. Here I discuss a novel approach to this challenge, focused on low-energy but composite quantum systems. The key insights is that quantum coherence of composite systems can be measurably affected by time dilation even at low-energies and in weak gravitational fields. I will explain the resulting new effects and how they can be tested. I will also discuss new insights into the Einstein Equivalence Principle (EEP) stemming from this approach, and sketch ideas for testing genuine quantum aspects of the EEP with composite quantum particles.

25 octobre 2018,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

A gravitational redshift test using eccentric Galileo satellites

Pacôme Delva

SYRTE

I will present the results of the analysis of the GREAT (Galileo gravitational Redshift test with Eccentric sATellites) experiment from SYRTE (Observatoire de Paris), funded by the European Space Agency. An elliptic orbit induces a periodic modulation of the fractional frequency difference between a ground clock and the satellite clock, while the good stability of Galileo clocks allows to test this periodic modulation to a high level of accuracy. Galileo 201 and 202, with their large eccentricity and on-board H-maser clocks, are perfect candidates to perform this test. SLR data allows us to partly decorrelate the orbit perturbations from the clock errors. By analyzing several years of Galileo satellites data we have been able to improve on the GP-A test of the gravitational redshift.

15 novembre 2018,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Antihydrogen Spectroscopy and Beyond

Niels Madsen

Swansea University

Antihydrogen, the bound state of an antiproton and a positron, is a very attractive system for probing a number of fundamental symmetries of physics such as the CPT theorem and the weak equivalence principle. The attractiveness stems from it being the only bound system of antimatter readily available, its neutrality and the detailed understanding of its matter counterpart, hydrogen, both theoretically and experimentally [1]. The ALPHA experiment produces and traps antihydrogen in order to subject it to precise measurements of e.g. its internal energy levels. According to the CPT theorem the transitions in antihydrogen must mirror those of hydrogen. I will present ALPHAs start-of-the-art antihydrogen production and trapping system [2] as well as discuss the first precise measurements on the internal states of antihydrogen [3, 4]. One example is ALPHAs most recent measurement of one hyperfine component of the 1S-2S transition in Antihydrogen to a precision of 2 parts in 1012, currently the most precise and accurate measurement on antimatter [4]. I will further discuss ALPHA‘s ongoing expansion with an experiment to probe the gravitational to inertial mass of antihydrogen, and I will discuss, various efforts that we believe will both increase the number of anti-atoms trapped as well as lower their temperature, allowing measurements whose precision will compete with that of hydrogen (e.g. Ref. [6]).
[1] Antiproton physics in the ELENA era (eds. N. Madsen), Phil. Trans. Roy. Soc. A, 376 (2018).
[2] Antihydrogen accumulation for fundamental symmetry tests, M. Ahmadi et al., Nat. Comm. 8, 681 (2017).
[3] Observation of the hyperfine spectrum of antihydrogen, M. Ahmadi et al., Nature 548, 66 (2017)
[4] Characterization of the 1S-2S transition in antihydrogen, M. Ahmadi et al., Nature 557, 71 (2018).
[5] Observation of the 1S-2P Lyman- transition in antihydrogen, M. Ahmadi et al., Nature 561, 211 (2018).
[6] Antihydrogen trapping assisted by sympathetically cooled positrons, N. Madsen, F. Robicheaux and S. Jonsell, N. J. Phys
16, 063046 (2014).

21 novembre 2018,
11h00

Danjon (Paris)

Photonic microwave signals with unprecedented phase noise

Xiaopeng Xie

SYRTE

In this talk, I will summarize my four years post-doc work on the topic of ultra-low phase noise microwave generation with the stabilized optical frequency comb. Photonic synthesis of radiofrequency revived the quest for unrivalled microwave purity by its seducing ability to convey the benefits of the optics to the microwave world. I will present a high-fidelity transfer of frequency stability between an optical reference and a microwave signal via a low-noise fiber-based frequency comb and cutting-edge photo-detection techniques. I will show the generation of the purest microwave signal with a fractional frequency stability below 6.5 x 10-16 at 1s and a timing noise floor below 41 zs.Hz-1/2 (phase noise below -173 dBc.Hz-1 for a 12 GHz carrier). This outclasses existing sources and promises a new era for state-of-the-art microwave generation. The characterization is achieved through a heterodyne cross-correlation scheme with lowermost detection noise. This unprecedented level of purity can impact domains such as radar systems, telecommunications and time-frequency metrology. The measurements methods can benefit the characterization of a broad range of signals.

22 novembre 2018,
13h30

Danjon (Paris)

Fondements du système international d’unités : géométrie, action et entropie

Christian Bordé

SYRTE

L’année 2018 est celle du renouvellement complet du système d’unités avec l’ambition d’établir un système pérenne, universel et cohérent. Ce système se caractérise par l’abandon des artefacts pour se fonder uniquement sur les constantes fondamentales de la Physique. La cohérence sous-jacente du système proposé et la notion de constante fondamentale seront discutées. Un système d’unités naturelles
a été introduit par Max Planck en 1899. Il est fondé sur cinq constantes fondamentales hbar, kB, c, G, epsilon0. Les deux premières concernent respectivement les mouvements cohérents et la décohérence thermique dans l’espace des phases au moyen des concepts d’action et d’entropie. Les trois dernières précisent la géométrie de cet espace en présence d’interactions gravitationnelles et électromagnétiques. Cette géométrie est celle d’un espace à cinq dimensions introduit par Theodor Kaluza en 1921. Les progrès considérables des interféromètres à ondes de matière dans les domaines atomique et électrique imposent aujourd’hui un nouveau système dans lequel les deux dernières constantes sont plutôt une différence de masse entre niveaux d’un même atome et la charge de l’électron. La cinquième dimension est alors le temps propre donné par les horloges atomiques. Le lien entre les deux systèmes fait intervenir la constante de structure fine et son équivalent gravitationnel. Le système proposé apparaît alors comme le meilleur compromis dans l’état actuel de nos connaissances.

13 décembre 2018,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

LNE-SYRTE (Ultra) Cold Atom Gravimeter

Romain Karcher

LNE-SYRTE

The LNE-SYRTE Cold Atom Gravimeter (CAG) is a quantum inertial sensor which operates since 2009. It performs 3 gravity measurements per second with laser cooled Rubidium-87 atoms using two-photon Raman transitions to realize an atomic interferometer. The CAG is a state of the art instrument which has demonstrated a short term sensitivity of 5.6µGal in 1s measurement time [1] and 0.06µGal in 40 000s (1µGal = 10-8m.s-2 ~10-9g).
Its design makes it movable, able to perform on field measurements and participate to international comparisons. Since the first Key Comparison CCM.G-K1 at BIPM (ICAG-2009) [2], its capabilities have been regularly compared to other technologies and its gravity measurements agree with the Key Reference Values of ICAG-2009, ECAG-2011 [3] and ICAG-2013 [4].
The total accuracy budget was dominated for a long time by the uncertainty on the effect of wavefront aberrations (4 µGal) which are today the major source of bias uncertainty in state of the art sensors using light beam splitters. To overcome these limits, we used ultracold atoms as a source and were able to reduce the evaluation of this uncertainty by a factor three thus reaching an unprecedented total accuracy budget uncertainty of 2µGal [5]. Now it has become relevant to tackle other effects such as two photon light shift. For that purpose we implemented a direct measurement of the Raman power.
In this talk I will present the CAG and its principle, and then focus on the benefit brought by ultracold atoms to the metrological study of free falling atom interferometers. By tackling their main limitation, our method allows reaching record-breaking accuracies for inertial sensors based on atom interferometry. I will finally discussed the new development performed toward a better monitoring of the Raman power before concluding on the future projects to reach sub-µGal complete uncertainty budget.
References
[1] P.Gillot et al, Metrologia 51 (2014)
[2] Z.Jiang et al, Metrologia 49 (2012)
[3] O.Francis et al, Metrologia 50 (2013)
[4] O.Francis et al, Metrologia 52 Tech.Suppl (2015)
[5] R.Karcher et al, New J. Phys. 20, 113041 (2018)

17 janvier 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Spectral hole burning, from laser stabilization to opto-mechanical sensing

Nicolas Galland

LNE-SYRTE

Rare-earth ions doping a crystalline matrix show optical transitions with very good coherence properties. At cryogenic temperature, it is possible to burn spectral features exhibiting few kHz linewidth, a life time longer than a day and other interesting properties. The very low temperature of the crystal theoretically ensures a very small brownian motion, which can make spectral hole a good candidate for stabilizing laser frequencies. Moreover, the strong coupling between the ions and their crystalline environment makes the hole sensitive to mechanical constraints. This optomechanical coupling could be used, for example, to probe very small motion of a micro-resonator carved into the crystal. In this seminar, I will present the SHB experiment in SYRTE and the recent improvement done in the field of laser stabilization as well as the measurement that have been done to characterize hole's frequency coupling to mechanical constraints and future applications.

24 janvier 2019,
11h00

Danjon (Paris)

Towards a quantum-enhanced trapped-atom clock on a chip

Mengzi Huang

LNE-SYRTE

Attention, changement de salle

The standard quantum limit (SQL) has become the ultimate fundamental noise source for state-of-the-art atomic clocks and atom interferometers. Nevertheless, the use of entanglement, especially of spin-squeezed states, can enable metrology beyond the SQL in measurements of collective states. Spin squeezing can be produced in quantum non-demolition (QND) measurements of the collective spin, particularly with cavity-quantum electrodynamical (QED) interactions. Despite the exceptional progress in achieving higher levels of squeezing, applying these quantum protocols at a metrological level of precision remains a challenge.
In this seminar, I will present the second generation of Trapped Atom Clock on a Chip (TACC) experiment at SYRTE, in which we realized a cavity-QED system on an atom chip, aiming at exploring spin-squeezing for a clock at 10E-13 stability level. Preliminary results of spin squeezing will also be presented.

31 janvier 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

ACES-PHARAO test of the gravitational redshift. Refined estimation of the expected sensitivity

Etienne Savalle

LNE-SYRTE

Using simulation and analysis software dedicated to the ACES-PHARAO mission, we estimate a statistical uncertainty in the low 10^-6 for the gravitational redshift test with the mission specifications of clock and link stability. Assuming a sufficient control of systematic frequency offsets (at the 10^-16 level), this would be a significant improvement on the best previous test (GP-A, 1976) which achieved about one part in 10^4 . Secondly, using highly deteriorated ISS orbit determination, we find that orbit errors of up to 1km would still allow to reach this uncertainty.

7 février 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Long-term stability and accuracy of the SYRTE cold-atom gyroscope

Matteo Altorio

LNE-SYRTE

Cold-atom inertial sensors target several applications in navigation, geoscience and tests of fundamental physics. I will present the SYRTE cold-atom gyroscope-accelerometer experiment, which has been built to study generic techniques for Atom-Interferometry and perform accurate and stable rotation rate measurements.
I will report on the latest results obtained with our setup: the improvement of the sensitivity and long-term stability reached by interleaved measurements. I will also present our recent studies on the accuracy of the gyroscope-accelerometer.

14 février 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Towards using a 2D magneto-optical trap to improve a mercury optical lattice clock

Valentin Cambier

LNE-SYRTE

Neutral mercury is a promising candidate to build an optical lattice clock thanks to several atomic properties.
In this seminar I will report on the recent improvements of the mercury optical lattice clock based on 199Hg.
In particular I will describe how the exploitation of a 2D Magneto Optical Trap (2D-MOT) allowed us to increase significantly the number of useful atoms gathered in a given time.
As a consequence we were able to decrease the loading time of the mercury optical lattice clock, so as the cycle time, that is the main factor of the Dick effect.
In a second part I will also present some results of the finer link comparison of december 2018.
Finally I will discuss about the perspectives and particularly about the lifetime measurements of the excited states.

21 février 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Ultrastable optical resonators with low-noise crystalline coatings

Garrett D. Cole

Crystalline Mirror Solutions LLC and GmbH

Substrate-transferred crystalline coatings are a groundbreaking new concept in optical interference coatings. Building upon fundamental research in cavity optomechanics, these “semiconductor supermirrors” were first demonstrated in 2013, with the key advantage being the ability to simultaneously achieve ultralow levels of optical and mechanical losses. With continuous refinement in epitaxial growth and layer transfer, we have now realized significant improvements in the limiting performance of these novel single-crystal multilayers. In the near-infrared (NIR), for center wavelengths spanning 1064 to 1560 nm, we have reduced the scatter + absorption losses to < 3 parts per million (ppm), enabling a cavity finesse exceeding 600,000 (equivalent to a reflectance > 99.9995%) at the telecom-relevant wavelength range near 1550 nm. Investigations in the mid-IR (MIR) spectral region also show exceptionally low levels of optical losses, with measurements yielding absorption below 50 ppm for wavelengths out to 4500 nm. Taken together, our NIR coatings are now fully competitive with ion beam sputtered films, while our prototype MIR optics have reached state-of-the-art performance levels. Looking ahead, we see a bright future for GaAs/AlGaAs-based crystalline coatings in applications requiring the ultimate levels of optomechanical performance.

28 février 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Dual gravi-gradio-meter with atom interferometry

Romain Caldani

LNE-SYRTE

Atom interferometry allows for the realisation of high performance inertial sensors based on laser cooled atoms. Latest advances permit fast preparation of ultracold Atom sources to sub-nK temperatures. Moreover, more robust and more powerful lasers are now available. Atom interferometers taking advantage of these progresses will constitute a next generation of inertial sensors, based on new geometries, and with improved performances. In this context, we are developing a dual sensor measuring both gravity and its vertical gradient offering in principle the possibility to resolve, by combining these two signals, the ambiguities in the determination of the positions and masses of the sources, which open new perspectives for applications.
The instrument will combine: (i) two ultra-cold sources obtained with atom chips based magnetic traps and (ii) powerful lasers to drive the atoms. These two key points will be combined to realise interferometers based on large momentum transfer beamsplitters of hundreds of hk (instead of 2hk previously) in a fountain configuration. For a cycling time of 2 s, the expected differential sensitivity is 1.3 10^-11 g.Hz^-1/2 for a detection limited by the quantum projection noise. As the two clouds are separated by 1 m, this will lead to a sensitivity on the vertical gradient of 126 mE.Hz^-1/2 in the laboratory (1 E = 10^-9 s^-2). Such a level of performances open new prospects for on field and on board gravity mapping, for drift correction of inertial measurement units in navigation, for geophysics and for fundamental physics.
I will present the instrument and the results we have obtained so far with laser cooled atoms. First, we performed the experimental demonstration of a method proposed earlier [1] to extract the differential
phase in dual atom interferometers. From two atomic sources, vertically separated and free falling synchronously, we drive simultaneous Raman interferometers onto the two sources and use the correlation with the vibration signal measured by a seismometer to extract the phase of each interferometer. We demonstrate an optimal sensitivity of the extracted differential phase between the two interferometers, free from vibration noise and limited by detection noise, when the two interferometers are in phase [2].
Second, we proposed a method for the accurate measurements of both the gravity acceleration and its vertical gradient using a dual atom interferometer, in principle free from any uncertainty related to the absolute or relative positions of the two atomic samples. The method relies on the use of a dual lock technique, which stirs simultaneously the chirp rate applied to the frequency difference between the interferometer lasers to compensate the gravity acceleration, and the frequency jump applied to the lasers at the mid pulse of the interferometer to compensate for the gravity gradient. This allows in the end to determine the two inertial quantities of interest in terms of frequencies [3].
Finally I will present the next steps of the project.
References
[1] Franck Pereira dos Santos, Differential phase extraction in an atom gradiometer, Phys. Rev. A 91 063615 (2015)
[2] Mehdi Langlois, Romain Caldani, Azer Trimeche, Sébastien Merlet and Franck Pereira dos Santos, Differential phase extraction in dual interferometers exploiting the correlation between classical and quantum sensors, Phys. Rev. A 96 053624 (2017)
[3] Romain Caldani, Kanxing Weng, Sébastien Merlet and Franck Pereira dos Santos, Simultaneous accurate determination of both gravity and its vertical gradient, arXiv:1812.09199 (2018)

14 mars 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Realization of two Rb fountains for timescale generation

Luca Lorini

Two Rb fountains have been realized in the framework of an international scientific and commercial collaboration among SYRTE, MuQuans and VREMYA-Ch (Russian private company). The fountain have been installed at VNIIFTRI (the national metrological institute of Russia) and are currently used for timescale generation. This presentation will concern all the stages of the project: the design, the realization and the installation at VNIIFTRI, focusing on the role of SYRTE. The fountains can run completely autonomously for long periods and do not require any routine maintenance. The fountains have cumulated now several months of continuous operation, showing state-of-the-art stability performances.

21 mars 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Twin atom sources: Emitting atom pairs in strongly correlated states

Marie Bonneau

Technische Universität Wien

We are developing in Vienna a source of momentum-entangled twin atoms. Twin atoms are the atomic analog of the twin photons generated through parametric down-conversion, which are widely used in optical quantum technologies.
Twin atoms are emitted from a source Bose-Einstein condensate through an atomic four-wave mixing process, where the non-linearity is provided by the interatomic interactions. The geometry of the experiment sets the phase-matching conditions and therefore defines the signal and idler modes populated by the atoms. Over the past years it was experimentally demonstrated that twin atoms share some properties with twin photons: their relative intensity is squeezed and they exhibit momentum correlations [1]. We report here the emission of twin atom beams in a double-well trapping potential, a geometry where the twin beams are expected to be Bell-entangled [2].
We trap and manipulate the atoms with an atom chip, which consists of a surface with micro-fabricated structures generating magnetic fields. It permits implementing fast and accurate deformations of the magnetic potential. With the atom chip we perform high-fidelity quantum optimal control of the BEC’s motional state [3]. We thus initialize the twin-atom source. We then characterize the correlation properties of the emitted twin atoms.
[1] R. Bücker et al., Nat. Phys. 7, 608–611 (2011).
[2] M. Bonneau et al., Phys. Rev. A 98, 033608 (2018)
[3] S. Van Frank et al., Scientific reports 6, 34187 (2016)

28 mars 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Spectral purity transfer for optical atomic clocks

Hector Alvarez Martinez

LNE-SYRTE

Optical frequency combs (OFCs) and ultra-stable lasers are key elements opening the way to optical clocks at the 10^-18 level. While the quantum projection noise certainly allows levels below 10^-17/t^1/2 for 10^4 atoms probed simultaneously (t being the integration time), the residual frequency noise of the local oscillator probing the narrow atomic resonance leads to the so-called Dick effect, limiting even the best optical clocks to a few 10^-16/t^1/2
In this context, it is very convenient to build ultra-stable lasers at wavelengths where components and spectrally pre-narrowed lasers are available such as the band 1530 nm – 1565 nm (C-band, used for optical infrared telecommunications). Regardless of the laser stabilization method used to this end, it is necessary to transfer the stability of the best SYRTE optical oscillator (master laser) to others target metrological wavelengths such as 698 nm for Sr, 1062 nm for Hg, and 1160 nm for SHB (slave lasers). This is achieved via an OFC operated, in our case, in the “narrow linewidth regime” and by the so called transfer oscillator technique, applicable even when the wavelengths of the master and slave lasers are far apart.
First, I will briefly introduce the frequency chain architecture together with the OFC, the core of the chain, which allows us to link the microwave and optical domains. I will describe how two optical clocks are compared both locally and internationally, and I will comment the services that we can offer to those who want to compare against our system.
Second, I will show an easy and reliable way to deal with one of the two degrees of freedom of the OFC, its carrier envelope offset (CEO) frequency. Our approach presents several benefits while being still compatible with the most advanced optical clocks accuracy results and spectral purity transfer methods.
Finally, I will present a new OFC based scheme transferring 6x10^-16 at one second from a 1542 nm wavelength laser (reference channel for the European fiber link) to a 1062 nm laser (metrological probing of the 199Hg atoms, after frequency quadrupling), a 698 nm laser (probe laser for the 87Sr atoms) and a 1062 nm laser (laser based on the spectral hole burning technique). With a residual noise due to the transfer in the 10^-18 range, I will show the potential and the main advantages of this new approach with respect to others, already done here at SYRTE and other laboratories, and its possible limitations regarding the final residual noise introduce by the transfer itself.

4 avril 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Implementation of a software-defined radio receiver on two-way satellite time transfer and calibration

Yi-Jiun Huang

LNE-SYRTE

For timekeeping demand, comparison among clocks far apart is required. To compare the time scales distributed in Asia, Europe and America is a challenge. The two-way satellite time and frequency transfer (TWSTFT) links two time scales in different places by carrying the clock ticks to the other sides through microwave signals and a telecommunication satellite. Currently used TWSTFT can offer 10^-15 stability to compare frequency difference at one-day average, and it can also offer 1 ns uncertainty to calibrate time-scale difference. As the clock precision growths rapidly, the Consultative Committee for Time and Frequency working group on TWSTFT aims at improving the stability and uncertainty. Recently, a software-defined radio receiver has been developed in LNE-SYRTE and TL and implemented on most TWSTFT links, demonstrating higher stability in time-scale comparison and potentially lower calibration uncertainty.

11 avril 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

The DAMNED experiment - DArk Matter from Non Equal Delays

Etienne Savalle

LNE-SYRTE

"DArk Matter from Non Equal Delays” (DAMNED) is a new experiment that aims to check for space or time variation of physics fundamental constants. This 3 arm Mach-Zender experiment allows us to compare an ultra-stable cavity to itself in the past through the delay created by a multi kilometer long optical fiber. A massive scalar dark matter field (DM) would be seen on the experiment beat and we aim to constrain a new combination of the DM coupling constants.

18 avril 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

A new experiment to test parity symmetry in cold chiral molecules using precise vibrational spectroscopy

Benoît Darquié

LPL

Parity violation has never been observed in chiral molecules. Inherent in the weak force, one of the four fundamental forces, parity violation should lead to a tiny energy difference between the enantiomers of a chiral molecule. This in turn leads to frequency differences in their rovibrational spectra, potentially measurable using precise mid-infrared spectroscopic measurements. A successful measurement will shed some light on the mystery of biomolecular homochirality and will also be a sensitive probe of fundamental physics.
We present our ongoing work towards developing the technologies needed for measuring parity violation in chiral molecules via Ramsey interferometry in the mid-infrared. This includes amongst other things developing frequency stabilised quantum cascade lasers calibrated to some of the world’s best frequency standards and a buffer-gas source of organo-metallic species of interest for a parity violation measurement formed using laser ablation of solid-state molecules in a cryogenic cell containing gaseous helium at 4 K.
We also present the results of preliminary spectroscopic investigations conducted on various species, in particular methyltrioxorhenium (MTO), an achiral test molecule from which promising chiral derivatives have recently been synthesized.
The methods we develop constitute new techniques for measuring and controlling complex molecules and open up new possibilities beyond parity violation for using them for other tests of fundamental physics, and for other applications in physics, chemistry, and technology.

25 avril 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

A definition of the SI second with optical clocks

Jérôme Lodewyck

LNE-SYRTE

The current SI second based on the atomic hyperfine transition in the ground state of 133Cs is expected to be replaced by a new definition based on optical frequency standards, whose uncertainty has now been established two orders of magnitude lower than the accuracy of the best Cs primary standards. However, such a redefinition of the second is hindered by the fast evolution in the field of optical frequency metrology, and by the fact that many atomic species are potential contenders to become the new frequency standard. We propose a possible definition of the frequency unit based on optical clocks that is compatible with these two issues, and therefore could be readily adopted.

16 mai 2019,
11h00

rdc Bât B (Paris)

Design and implementation of an atom interferometer for inertial sensing with an atomchip

William Dubosclard

LNE-SYRTE

Attention, salle inhabituelle

In this work the development of an atomchip based compact cold atom inertial sensor is presented. I will discuss the relevant criteria to be considered when developing such a sensor for inertial navigation. In
particular, the experimental realization of our sensor will use magnetically guided 87Rb atoms. The
magnetic guide is produced by current carrying wires microfabricated on the chip. For this reason, I
will present the characterization of the fabricated atomchip in terms of wire roughness, a critical parameter when using guided matter waves for atom interferometry. This roughness is quantify in terms of its power spectral density, extracted from scanning electron microscopy measurements. The measured rms roughness is 5,9×10-5 µm3 over 20 µm wire length, producing a peak-to-peak magnetic roughness potential of
325 nK/A at 20 µm from the chip surface. I will show that the size of this potential is compatible with free atom propagation in the designed magnetic guides. Moreover, I will discuss the optical setup we develop
to produce the splitting and deflection of the atoms by Bragg transitions.

23 mai 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

A pirate signal nearby the GNSS L1-Band jamming OP GNSS stations

Pierre Uhrich

LNE-SYRTE

LNE-SYRTE in Observatoire de Paris (OP, Paris, France) is operating an ensemble of different GNSS stations which stayed over years close to each other in the ns range. In addition, since the change of calibrated delays in GPS receivers (February 2017) and of the reference delay value in the Two-Way Satellite Time and Frequency Transfer (TWSTFT) OP station (March 2017), the offsets between GPS Common-View (CV) and TWSTFT were remaining below 2 ns on the links between UTC(OP) and a selection of remote UTC(k). But at the end of November 2018, a large discrepancy either between the different OP GNSS stations or between GPS CV and TWSTFT, together with an irregular loss of GNSS data, could be observed. Because all OP GNSS stations were not impacted similarly, some local equipment failure was suspected first. But when a spectrum analyzer was connected to one of the GNSS antennas, the cause was easily identified. Just below the GNSS L1-band, a powerful signal more than 35 dB above the GNSS signal level is clearly visible. This signal level is indicating that the unexpected signal is transmitted from the ground nearby OP. But, according to the international frequency table of the International Telecommunication Union (ITU), the frequency band 1535-1559 MHz is formally allocated to satellite telecommunication downlink for institutional users. This is therefore a pirate signal. A formal complaint, raised early January 2019 to the French National Frequency Agency (ANFR), is currently under process. The pirate signal has been changing with time, and we observed different kinds of perturbations on the OP GNSS stations, which will be described.

11 juin 2019,
11h00

rdc Bât B (Paris)

Novel methods for measuring the gravitational constant in space

Jonathon Baird

Astroparticule et Cosmologie - Paris, Université Paris Diderot

Attention salle inhabituelle

The gravitational constant, or 'Big G', is one of the least constrained elements in the set of fundamental constants. Although recent measurements on ground have reached accuracies of parts in 10^5 there remains a discrepancy between measurements at almost parts in 10^3 at a significance of sometimes 5-10 sigma. With the success of the LISA Pathfinder experiment to test the technology for future space based gravitational wave observatories, the question was asked if space based interferometers could be added to the short list of experimental procedures to measure big G. This would allow a measurement in a gravitationally quiet environment, removing the large background of the Earths field and other parasitic forces that could be the cause of the observed scatter between terrestrial measurements. Furthermore, this would allow tests of various theories of gravity that call for modifications to Big G in low field environments. Two independent measurements of Big G, performed during the mission, are reported, and their methods compared and contrasted for feasibility in future dedicated space missions, with an emphasis on the complexity of each method and potential to reach competitive relative errors.

13 juin 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Iodine frequency stabilized Telecom laser sources

Joannes Barbarat

LNE-SYRTE

We have developed a compact optical frequency standard based on an infrared laser operating in the C-band Telecom domain (~ 1544 nm), frequency stabilized against a narrow iodine transition located in the green range of the visible domain (~514.5 nm). The frequency gap between the IR and the green ranges is bridged in an efficient way using a frequency tripling process, based on two cascaded LiNbO3 nonlinear crystals. The compact design of the whole setup will make it easily transportable in order to be used outside regular metrology laboratories, as an ultra-stable optical frequency reference. The whole optical setup occupies a volume of 27 litres, which will be reduced below 10 litres in the coming months. We have already demonstrated a frequency stability of 4.6*10^-14 t^-1/2 for this preliminary development.

20 juin 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Theory and experiment of precision spacetime-symmetry tests

Quentin Bailey

Embry-Riddle Aeronautical University

In this talk, recent developments in describing generic breaking of spacetime symmetries, notably local Lorentz and CPT symmetry, will be discussed. I will summarize key result results, observational and experimental limits, and discuss specifics for tests on Earth and in space. Also, I will discuss some progress in connecting some quantum gravity models with effective field theory frameworks for tests of spacetime symmetries.

4 juillet 2019,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Ultracold atoms carrying orbital angular momentum: Quantum sensing and topology

Veronica Ahufinger

Departament de Física, Universitat Autònoma de Barcelona

Pushing the limits of sensing technologies is one of the main challenges in modern physics, opening the door to high-precision measurements of fundamental constants as well as applications in many different areas of science. On the other hand, since the observation of the quantum Hall effect in two-dimensional electron gases and the discovery of its relation with topology, the study of systems with non-trivial topological properties has become a central topic in condensed matter physics. In this talk, we will show that ultracold atoms carrying orbital angular momentum (OAM) constitute a novel platform to explore both scenarios.
In particular, we propose a quantum sensing device to measure with high sensitivity non-linear interactions, scalar magnetic fields and rotations [1]. It consists in an imbalanced superposition of OAM modes of a Bose–Einstein condensate (BEC) in a ring trap with opposite winding numbers, for which a minimal atomic density line appears. A weak two-body interaction between the atoms of the BEC leads to a rotation of the minimal atomic density line whose angular frequency is directly related to the strength of such interactions. We derive an analytical model relating the angular frequency of the minimal density line rotation to the strength of the non-linear atom-atom interactions and the difference between the populations of the counter-propagating modes. Additionally, we propose a full experimental protocol based on direct fluorescence imaging of the BEC that allows measuring all the quantities involved in the analytical model and use the system for sensing purposes.
In the context of topology, we study the single-particle properties of a system formed by ultracold atoms loaded into the manifold of l=1 OAM states of an optical lattice with a diamond chain geometry [2,3]. Through a series of successive basis rotations, we show that the OAM degree of freedom induces phases in some tunneling amplitudes of the tight-binding model that are equivalent to a net pi flux through the plaquettes and give rise to a topologically non-trivial band structure and protected edge states. In addition, we demonstrate that quantum interferences between the different tunneling processes involved in the dynamics may lead to Aharanov-Bohm caging in the system. All these analytical results are confirmed by exact diagonalization numerical calculations.
[1] G. Pelegrí, J. Mompart and V. Ahufinger, Quantum sensing using imbalanced counter-rotating Bose-Einstein condensate modes. New Journal of Phys. 20, 103001 (2018).
[2] G. Pelegrí, A. M. Marques, R. G. Dias, A. J. Daley, V. Ahufinger and J. Mompart, Topological edge states with ultracold atoms carrying orbital angular momentum in a diamond chain. Phys. Rev. A 99, 023612 (2019).
[3] G. Pelegrí, A. M. Marques, R. G. Dias, A. J. Daley, J. Mompart and V. Ahufinger, Topological edge states and Aharanov-Bohm caging with ultracold atoms carrying orbital angular momentum. Phys. Rev. A 99, 023613 (2019).

### Saison 2017-2018 :

21 septembre 2017,
11h00

Danjon (Paris)

A noise-immune cavity-assisted non-destructive detection for an optical lattice clock in the quantum regime

Grégoire Vallet

LNE-SYRTE

We present and implement a non-destructive detection scheme for the transition probability readout of an optical lattice clock. The scheme relies on a differential heterodyne measurement of the dispersive properties of lattice trapped atoms enhanced by a high finesse cavity. By design, this scheme offers a 1st order rejection of the technical noise sources, an enhanced signal-to-noise ratio, and an homogeneous atom-cavity coupling. We theoretically show that this scheme is optimal with respect to the photon shot noise limit. We experimentally realize this detection scheme in an operational strontium optical lattice clock.
The resolution is on the order of a few atoms with a photon scattering rate low enough to keep the atoms trapped after detection. This scheme opens the door to various different interrogations protocols, which reduce the frequency instability, including atom recycling, zero-dead time clocks with a fast repetition rate, and sub quantum projection noise frequency stability.

5 octobre 2017,
11h00

Salle JF Denisse (ex salle de l'Atelier) (Paris)

Métrologie quantique et symétries relativistes

Serge Reynaud

LKB

La métrologie moderne est basée sur la physique quantique et relativiste. La seconde est définie comme un nombre entier de périodes d’une horloge atomique et le mètre est dérivé de la valeur fixée pour la vitesse de la lumière dans le vide. Bientôt, la constante de Planck et la charge élémentaire devraient être également définies avec des valeurs exactes remplaçant les anciennes définitions du kilogramme et de l'ampère.
Le statut quantique des observables associées au temps, à l'espace, à la masse, leur compatibilité avec les symétries relativistes restent pourtant des questions ouvertes. On discutera d’abord de manière qualitative ces questions à l’interface entre métrologie, physique quantique et relativité. On présentera ensuite un cadre théorique où les observables sont définies de manière à être compatibles à la fois avec les exigences relativistes et quantiques.
Dans cette approche, la masse observable n'est plus une constante, comme on peut le deviner en raison de sa dimension par rapport à la dilatation. Les transformations des observables vers des référentiels accélérés diffèrent de leurs homologues classiques. Les symétries relativistes permettent néanmoins d'étendre les règles de covariance de la relativité, ce qui conduit à une version quantique du principe d'équivalence d'Einstein identifié à la transformation de la masse observable.

24 octobre 2017,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Space-based ultra-high precision time & space reference

Yansong Meng

China Academy of Space Technology (CAST Xi’an)

CAST Xi’an is a subsidary of China Academy of Space Technology(CAST) within China Aerospace Science and Technology Corporation(CASC). CAST Xi’an is mainly engaged in developing and producing spacecraft payload and electronic systems and equipment, spacecraft measurement and control, and satellite electronic systems and equipment, as well as researching in the corresponding electronics. CAST Xi’an is the most important provider of satellite payload in China, taking over 80% of Chinese current developing tasks in orbit satellite payloads.
In the field of satellite navigation technology, the Xi’an branch has completed the development tasks of the payload for all navigation satellites of Beidou I and Beidou II. At present, the development of Beidou III payload is under way. In the field of time-frequency technology, high precision rubidium clock has successfully motioned in orbit, with the frequency stability at 2E-14/day. Currently, the very high precision rubidium clock is under development, whose frequency stability reaches 3E-15/day. Meanwhile, other high performance time-frequency products are also developed, such as a high stability crystal oscillator and frequency synthesizer, etc., in the field of navigation technology, it has developed Beidou navigation satellite’s descending navigation signal generation and broadcast downlink load, and in L band, the satellite-ground time comparison precision is 0.6 ns, and time-frequency transfer stability up to 1E-15/day; in the inter-satellite time and frequency transfer field, inter-satellite time synchronization based on Ka band reaches 0.6 ns, and time-frequency transfer stability up to 1E-15/ day.
At present, CAST Xi’an is developing to the next generation satellite navigation system, and now it is carrying out the research and demonstration of ongoing space-based ultra high precision space-time reference technology, which is based on the ion clock, space optical frequency comb and narrow linewidth laser as the core, generating microwave and laser time-frequency signal with high performance, and frequency transfer between satellite, and generating and maintaining the space-time datum with high precision. Its core technology includes cold mercury ion clock, microwave / laser coherent time-frequency system, ultra high precision time and frequency transfer technology and so on, supporting scientific research in satellite navigation, geodesy and other space science.

23 novembre 2017,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Search for the electric dipole moment of the neutron

Guillaume Pignol

Laboratoire de Physique Subatomique et de Cosmologie (CNRS-IN2P3)

Why is there so little antimatter in the Universe?
How the matter/antimatter asymetry was generated?
New physics, beyond the Standard Model, was certainly at play in an hypothetical phase of the early Universe called baryogenesis.
Since this new physics must induce a violation of CP symmetry, it could be revealed in the laboratory by measuring a nonzero electric dipole moment of a spin 1/2 particle such as the neutron.
A collaboration of 15 institutions is searching for the neutron electric dipole moment (nEDM) using the ultracold neutron source at the Paul Scherrer Institute (PSI) in Switzerland. The most precise measurement of the nEDM has been produced by the Sussex/RAL/ILL spectrometer at the ILL research reactor in Grenoble,
it is compatible with zero, with the upper limit dn< 3E-26 ecm @90% C.L. [J.M. Pendlebury et al. PRD 92, 092003 (2015)].
We have operated an upgraded version of this apparatus to take data at PSI in the period 2015-2017 and we are now building the next generation spectrometer, n2EDM.
In my talk I will present the current status of the measurement and discuss the statistical and systematical uncertainties.

29 novembre 2017,
13h00

Danjon (Paris)

Experiments with atom circuits

Fred Jendrzejewski

Universität Heidelberg

Horaire exceptionnel faute de salle disponible à 11h

Bose-Einstein condensates in ring geometries are essential ingredients to the ongoing effort of building increasingly complex superfluid circuits. Such circuits have previously allowed for the observation of
persistent currents and hysteresis. After discussion of those observations, I will report on another technique to directly observe the current-phase relationship through weak links. By interfering our ring with a phase reference (formed as a disk), we show that we can measure the phase of the BEC around the ring and the average current. Finally, I will discuss the possibility of quantum heat engines in atomic gases.

7 décembre 2017,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Laser spectroscopy on antihydrogen and fundamental symmetry tests

Bruno Ximenez Rodrigues Alves

Aarhus Univtersity - CERN

The universe is mainly composed by matter while the Standard Model of Particle Physics predicts that matter and antimatter should have been created in equal amount. The search for matter/antimatter asymmetry by the ALPHA collaboration at CERN is an effort to understand this discrepancy. The latest results on laser spectroscopy of trapped antihydrogen will be presented together with an overview of the experimental setup.

14 décembre 2017,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Ultracold Dysprosium: from laser cooling to non-classical spin states

Leonid Sidorenkov

LKB, LNE-SYRTE

A complex electronic structure of atomic Dysprosium gives rise to its rich spectrum of optical transitions, large ground-state electronic angular momentum and corresponding magnetic moment. These properties open exciting possibilities for quantum simulation with ultracold Dysprosium atoms.
In this talk, we will present an overview of the new Dysprosium experiment at LKB (College de France) and discuss our latest results on generating and characterizing non-classical spin states with ultracold Dysprosium atoms.

18 janvier 2018,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Studies for a top hat optical resonator and its application to atom interferometry

Nicolas Mielec

SYRTE

State of the art cold-atom inertial sensors use free falling, laser cooled, atoms at micro-Kelvin temperatures, and interrogation times of a few hundred milliseconds. These conditions lead to atom clouds with centimetric sizes, which require large laser beams and thus high power to be interrogated efficiently. In most implementations, difficulties to match these constraints result in contrast losses and systematic effects. We present our studies on the development of a top-hat optical resonator which could provide homogeneity of the intensity profile and power amplification. We have designed and realized a marginally stable optical resonator capable of supporting a large Gaussian beam, and studied techniques to produce a collimated top-hat beam. We have also investigated the effects of temporal shaping of the interrogation pulses, and applicability to atom interferometry based on large momentum transfer beamsplitters.

1er février 2018,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Proposal for a quantum test of the weak equivalence principle with entangled atomic species

Rémi Geiger

We propose an experiment to test the Weak Equivalence Principle (WEP) with a test mass consisting of two entangled atoms of different species. In the proposed experiment, a coherent measurement of the differential gravity acceleration between the two atomic species is considered, by entangling two atom interferometers operating on the two species. The entanglement between the two atoms is heralded at the initial beam splitter of the interferometers through the detection of a single photon emitted by either of the atoms, together with the impossibility of distinguishing which atom emitted the photon. In contrast to current and proposed tests of the WEP, our proposal explores the validity of the WEP in a regime where the two particles involved in the differential gravity acceleration measurement are not classically independent, but entangled. We propose an experimental implementation using 85Rb and 87Rb atoms entangled by a vacuum stimulated rapid adiabatic passage protocol implemented in a high finesse optical cavity. We show that an accuracy below 10-7 on the Eötvös parameter can be achieved.
Reference: Remi Geiger and Michael Trupke, “Proposal for a quantum test of the weak equivalence principle with entangled atomic species”, Phys. Rev. Lett. (in press)

29 mars 2018,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Sub-Doppler cooling of atoms using an optical frequency comb

Neven Šantic

Institute of Physics, Zagreb, Croatia

In this talk I will present results on sub-Doppler cooling of rubidium atoms on a dipole-allowed transition at 780 nm by using a frequency comb (FC). For this purpose we implement a scheme for full stabilization of a fiber based FC that does not require traditional self-referencing. We measure temperatures as low as 55 uK in a one-dimensional FC cooling geometry using the time-of-flight method. Laser cooling with FCs could enable achieving sub-Doppler temperatures for atoms with dipole allowed transitions in the vacuum ultraviolet, such as hydrogen, deuterium and antihydrogen.
I will also briefly mention two other topics I recently worked on: synthetic magnetism for cold atoms based on radiation pressure and the Doppler effect and nonlinear propagation of random classical waves which leads to a precondensation effect.

3 avril 2018,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

NIST Yb optical lattice clocks with uncertainties near 10^-18

Daniele Nicolodi

NIST

Daniele Nicolodi will give a seminar on his work at NIST on Yb optical
lattice clocks with uncertainties near 10^-18. The focus will be on the
development of ultra-stable lasers and on controlling the DC-stark shift
(see https://arxiv.org/abs/1803.10737 ).

5 avril 2018,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Experimental Fock-state in quantum memories

Luis Ortiz

INLN - Université Nice Sophia Antipolis

Quantum technologies such as quantum communication and quantum cryptography, need a key piece: the distribution of quantum states over long distances. The channels for the transmission of quantum information are mainly two, optical fibers and free space, at least for the case of qubits written in light. However, these channels have a fundamental problem, photon losses. In order to overcome such a limitation, in the last decades a scheme of quantum network has been proposed, which is constituted by quantum nodes and channels for interconnection. It uses light fields -as carriers of information through optical fibers- and matter, either as individual atoms or atomic ensembles to implement fixed nodes, which are able to store the information for a controlled period of time, also known as “quantum memories”. In this seminar I’m going to show an experimental work focused on the process of extraction of the quantum information from a quantum memory based on a cloud of cold Rubidium atoms. This stored information is originally packaged in a collective atomic mode, which could subsequently be extracted on demand in a light field, presenting non-classical correlations with a previously detected heralding field. A characteristic of the photons that mediate these interactions is that they are narrowband enough to allow a direct study of the temporal shape of their wave packet. Through the analysis and theoretical modeling of this wave packet, we investigate the extraction dynamics of the quantum information stored in the quantum memory. We report an experimental finding of non-classical characteristics of superradiance by implementing the process not only with a single excitation, but also with two-photon Fock states, which opens the way for the study of interactions between collective quantum memories and light modes in a regime of higher-order components of the electromagnetic field.

26 avril 2018,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Jet lent d’argon métastable et nanoréseaux : une piste pour des mesures de précision des interactions de Casimir-Polder entre atome et surfaces

Gabriel Dutier

Laboratoire de Physique des Lasers

Le potentiel Casimir-Polder entre atome et surface a été mesuré par de nombreuses expériences et sur une gamme de distances comprises entre quelques nanomètres à quelques dizaines de micromètres. Il apparait néanmoins que pour quasiment l'ensemble de ces expériences la contribution de l'interaction atome surface au regard du signal mesuré (diffraction, nombre d'atomes après rebond, etc..) reste très faible et l'accord avec une modélisation du potentiel Casimir-Polder est au mieux de l'ordre de 10%. Nous proposons des mesures de diffraction à travers un nanoréseau (fentes environ 50 nm) d'un jet d'atomes d'argon métastable de vitesse variable entre 10 et 150 m/s. Le temps de passage des atomes à l'intérieur du nanoréseau engendre une contribution de l'interaction atome surface nettement supérieure à la contribution purement géométrique de la diffraction. Le signal ainsi recueilli contient alors toutes les informations de géométrie du réseau ainsi que celle du potentiel Casimir-Polder mais dans des proportions très favorables à ce dernier. Je présenterai les expériences menées au laboratoire de physique des lasers, les limitations théoriques ainsi que les perspectives à une nouvelle mesure de contrainte sur la 5ième force par comparaison isotopique (36Ar).

17 mai 2018,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Searching for dark matter with GPS and global networks of atomic clocks

Ben Roberts

LNE-SYRTE

Dark matter constitutes 85% of all matter in the Universe, yet conclusive evidence for dark matter in terrestrial experiments remains elusive.
One possibility is that dark matter is composed from ultralight quantum fields whose self-interactions lead to the formation of dark matter objects in the form of stable topological defects.
As the Earth moves through the halo of dark matter objects, interactions with such dark matter clumps could lead to measurable variations in GPS signals that propagate through the satellite constellation at galactic velocities, allowing us to use the network of GPS atomic clocks as a 50 000 km aperture dark matter detector. I will discuss recent results, and the potential for the future.

21 juin 2018,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

High resolution optical inertial sensors for the third generation of gravitational wave detectors

Christophe Collette

Université Libre de Bruxelles

In order to detect gravitational waves, the mirrors of LIGO and Virgo must be isolated from seismic vibrations in a frequency range extending from 10 Hz to 1000 Hz, where the transmission of ground motion is reduced by up to 10 orders of magnitude. In LIGO and Virgo, this is currently achieved by a subtle combination of passive and active isolators. In the third generation of gravitational wave detectors (like the Einstein Telescope), the sensitivity will be further increased at low frequency, requiring a ultra-high performance seismic isolation system. To this purpose, a new generation of inertial sensors is required, combining a low sensitivity to thermal gradients and magnetic field, with a very high resolution. This talk will present the
motivations for such instruments, and describe the current status of our developments in this field.

### Saison 2016-2017 :

15 septembre 2016,
11h00

Salle de l'atelier (Paris)

Precision Measurement and Sensing for New Test of Fundamental Physics and the realization of Quantum Hybrid Systems

Michael Tobar

University of Western Autralia

A variety of precision experiments at the University of Western Australia (UWA) and in cooperation with other institutes, which utilise photons, phonons and electrons will be introduced. Pushing these technologies to operate with quantum limited precision and beyond allows new tests of fundamental physics as well as new technologies for future applications.
First we will present results in collaboration with Humboldt University of Berlin that shows ex-tremely new sensitive tests of GR capable of probing suppressed effects emanating from the Planck scale [1]. In this work we use two ultra-stable oscillator frequency sources to perform a modern Michelson-Morley experiment and make the most precise measurement to date of the spatial isotropy of the speed of light, constraining ?c/c to 9.2±10.7×10?19. This allows us to undertake the first terrestrial test of Lorentz invariance at the Planck-suppressed electroweak unification scale, finding no significant violation of Lor-entz symmetry.
Second, we show our progress in utilizing new microwave experiments to search for the Dark Sector Particles. Dark matter is a fundamental component of the universe yet the nature of its composition is still unknown. Through the development of remarkable precision electromagnetic measurement tools and techniques, we aim to perform a comprehensive laboratory search for dark matter axions at UWA in a mass ranges that are currently untested [2,3].
Third, we present the latest results from our cavity QED and spins in solids program, which aims to couple microwave photons strongly with spins at mK temperatures in the single photon regime using novel microwave cavities [4-8]. Some of this work has been done in collaboration with Saarland Univer-sity, Macquarie University and the Royal Melbourne Institute of Technology.
Finally, I present progress on the precision measurement of optomechanical and acoustic systems of macroscopic dimensions. The goal is to cool the system to the ground state and read it out with quantum-limited precision. Such massive systems can be used to also test fundamental physics, such as search for gravitational effects on the uncertainty relations [9], Lorenz Invariance Violations in the “phonon” sector, search for potential dark matter candidates and test for high frequency Gravitational Waves in the 5 to 500 MHz range [10-12].
References
[1] M Nagel, SR Parker, E Kovalchuck, PL Stanwix, J Hartnett, EN Ivanov, A Peters, ME Tobar “Direct Terrestrial Test of Lorentz Symmetry in Electrodynamics to 10-18,” Nature Comm., vol. 6, 8174, 2015.
[2] BT McAllister, SR Parker, ME Tobar, “Axion dark matter coupling to resonant photons via magnetic field,” Phys. Rev. Lett., vol. 116, 161804, 2016.
[3] BT McAllister, SR Parker, ME Tobar, 3D Lumped LC Resonators as Low Mass Axion Haloscopes, arXiv:1605.05427 [physics.ins-det] (under review at Phys. Rev. D)
[4] S Probst, A Tkalcec, H Rotzinger, D Rieger, J-M Le Floch, M Goryachev, ME Tobar, et. al., PRB, 90, 100404 (R), 2014.
[5] M Goryachev, WG Farr, DL Creedon, Y Fan, M Kostylev, ME Tobar, “High cooperativity cavity QED with Magnons at Microwave Frequencies,” Phys. Rev. Applied, vol. 2, 054002, 2014.
[6] M Goryachev, ME Tobar, “The 3D split-ring cavity lattice: a new metastructure for engineering arrays of coupled micro-wave harmonic oscillators,” New J. Phys. 17, 023003, 2015.
[7] DL Creedon, J Le Floch, Maxim Goryachev, WG Farr, S Castelletto, ME Tobar, “Strong Coupling Between P1 Diamond Impurity Centres and 3D Lumped Photonic Microwave Cavity,” PRB, vol. 91, 140408(R), 2015.
[8] J-M Le Floch, C Bradac, N Nand, S Castelletto, ME Tobar, T. Volz, “Addressing a single NV- spin with a macroscopic dielectric microwave cavity,” Appl. Phys. Lett., vol. 105, 133101, 2014.
[9] J Bourhill, E Ivanov, M Tobar, “Precision Measurement of a low-loss Cylindrical Dumbbell-Shaped Sapphire Mechanical Oscillator using Radiation Pressure,” arXiv:1502.07155 [physics.ins-det]
[10] A Lo, P Haslinger, E Mizrachi, L Anderegg, H Müller, M Hohensee, M Goryachev, ME Tobar, “Acoustic Tests of Lorentz Symmetry Using Quartz Oscillators,” Phys. Rev. X, vol. 6, 011018, 2016.
[11] M Goryachev, ME Tobar, “Gravitational wave detection with high frequency phonon trapping acoustic cavities,” PRD, 90, 102005, 2014.
[12] M Goryachev, DL Creedon, S Galliou, ME Tobar, “Observation of Rayleigh phonon scattering through excitation of ex-tremely high overtones in low-loss cryogenic acoustic cavities for hybrid quantum systems,” PRL., 111, 085502, 2013.

20 octobre 2016,
11h00

Salle de l'atelier (Paris)

Using Global Navigation Satellite Systems (GNSS) for time and frequency applications

Pascale Defraigne

Royal Observatory of Belgium, ROB

Global Navigation Satellite Systems (GNSS) are giving access not only to your position but also to timing information. Hence, GNSS are classically used for remote atomic clock and remote time scale comparisons as needed e.g. for the realization of UTC.
While the American Global Positioning System (GPS) has been used since the eighties, it is now time to start using the new constellations as well. This presentation will make the status of the Russian GLONASS, the European Galileo and the Chinese BeiDou systems and look at the possibilities they offer for time and frequency applications.

27 octobre 2016,
11h00

Salle de l'atelier (Paris)

A wave-guided Sagnac Interferometer for Bose-Einstein Condensates

Patrick Navez

Crete Center for Quantum Complexity and Nanotechnology - CCQCN

Guided matter wave interferometry offers the possibility to largely increase the duration of the individual measurement event, thus promising a large increase in sensitivity albeit at the cost of reduced precision. In this talk, we present a novel matter wave Sagnac interferometer based on state-dependent manipulation of
atoms. Waveguides based on time-averaged adiabatic potentials are generalized to the case of elliptic radio-frequency field. Taking advantage of the change in sign in the Zeeman energy, we derive distinct potential for even and odd hyperfine components. We analyze two following configurations, one where the two components are confined in two `buckets' and carried separately in the opposite direction through the ring, and one where these spin components are accelerated and decelerated within a wave guide. Corrections to the ideal Sagnac phase are also investigated by extending the area theorem beyond a purely adiabatic movement of the atoms.

17 novembre 2016,
11h00

Salle de l'atelier (Paris)

Experimental activity with large size ring laser gyroscopes

Jacopo Belfi

INFN, sezione di Pisa, Italy

Sagnac interferometry is currently a very promising research area for a variety of applications ranging from inertial navigation to geodesy to fundamental physics [1]. State of the art ring laser gyroscopes, based on large-frame high-finesse ring resonators, provide very precise measurements of the Earth rotation rate and today achieve a rotational resolution well below 1 prad/s at few hours integration time, paving the way to very interesting applications in Earth Science and also in General Relativity [2].
Three experiments [3-5] are ongoing by the Italian Institute of Nuclear Physics (INFN) on ring laser gyroscopes, aiming at the required performances for fundamental Physics applications. After a brief review of the state of the art in the field, I will show the performances, limitations, and perspectives of our developed prototypes.
References:
[1] K. U. Schreiber and J.-P. R. Wells, Rev. Sci. Instrum. 84, 041101 (2013)
[2] F. Bosi et al., Phys. Rev. D 84, 122002 (2011)
[3] A. Simonelli et al., Annals of Geophysics, 59 (2016)
[4] J. Belfi et al., Classical and Quantum Gravity 31 (22), 225003 (2014)
[5] N. Beverini et al. , Proceedings of the European Frequency and Time Forum (EFTF) 2016, 10.1109/EFTF.2016.7477837, (2016)

1er décembre 2016,
11h00

J.F. Denisse (ex salle de l'Atelier) (Paris)

Active control of laser wavefronts in atom interferometers

Mehdi Langlois

LNE-SYRTE

Wavefront aberrations are identified as a major limitation in quantum sensors. They are today the main contribution in the uncertainty budget of best cold atom interferometers based on two-photon laser beam splitters, and constitute an important limit for their long-term stability, impeding these instruments from reaching their full potential. Moreover, they will also remain a major obstacle in future experiments based on large momentum beam splitters. We tackle this issue by using a deformable mirror to control actively the laser wavefronts in atom interferometer. In particular, we demonstrate in an experimental proof of principle the efficient correction of wavefront aberrations in an atomic gravimeter.

8 décembre 2016,
11h00

J.F. Denisse (ex salle de l'Atelier) (Paris)

Cold atom interferometer of 39K and 87Rb to test the weak equivalence principle in microgravity

Antoni-Micollier Laura

LP2N

During the last two decades, new techniques to cool and manipulate atoms have enabled the development of inertial sensors based on atom interferometry. The ICE project aims to verify the weak equivalence principle (WEP), which is a cornerstone of the theory of the General Relativity. This principle postulates that the acceleration of a body in free-fall in a gravitational field is independent of its internal structure and composition. The WEP is characterized by the Eötvös parameter, which is a normalized difference between the acceleration of two test bodies. By using a compact and transportable dual-species atom interferometer, we compare the acceleration of two chemical species and verify their equality by measuring the Eötvös parameter at the 10-6 level. This experiment was performed both in the laboratory and in the microgravity environment during parabolic flights onboard the Novespace ZERO-G aircraft. The interferometer is composed of laser-cooled samples of 87Rb and 39K, which exhibit similar transition wavelengths (780 nm and 767 nm) derived from frequency-doubled telecom lasers.
Recently, we have performed the first dual species interferometer in microgravity. This enables the first test of the WEP in weightlessness using quantum objects, which represents a major first step toward future mission in space.
As part of these experiments, we have implemented a 770 nm laser source, resonant with the D1 transition of 39K, in order to perform a gray molasses which allows us to cool the atoms at 5 µK. We have also devised a new sequence to prepare atoms in the magnetically-insensitive state mF = 0 with a transfer efficiency above 90%. These techniques improved the contrast, and therefore the sensitivity, of our 39K interferometer by a factor 4. The achievement of the weak equivalence principle test in the laboratory with these improvements showed a sensitivity on the Eötvös parameter of 5.10-8 after 5000 s of integration.

15 décembre 2016,
11h00

J.F. Denisse (ex salle de l'Atelier) (Paris)

Continuous cold-atom gyroscope with 1 nrad/s stability

Denis Savoie

LNE-SYRTE

We report the operation of a cold-atom inertial sensor which continuously captures the rotation signal. Using a joint interrogation scheme, where we simultaneously prepare a cold-atom source and operate an atom interferometer (AI) enables us to eliminate the dead times. We show that such continuous operation improves the short-term sensitivity of AIs, and demonstrate a rotation sensitivity of 100 nrad.s^-1 in a cold-atom gyroscope of 11 cm² Sagnac area.
We also demonstrate a rotation stability of 1 nrad.s^-1 at 10^4 s of integration time, which establishes the record for atomic gyroscopes. The continuous operation of cold-atom inertial sensors will enable to benefit from the full sensitivity potential of large area AIs, determined by the quantum noise limit. I will present these results after presenting the SYRTE cold-atom gyroscope. I will also show methods to improve the sensitivity and the stability of the instrument like hybrid measurements that allowed to reach a stability of 0.5 nrad.s^-1.

5 janvier 2017,
11h00

J.F. Denisse (ex salle de l'Atelier) (Paris)

Effets d'interférences dans la décoherence induite par l'émission spontanée: un analogue de la superradiance avec un seul atome

François Impens

Instituto de Fisica / Universidade Federal do Rio de Janeiro

Nous montrons que des effets d'interférences permettent d'établir une analogie entre la superradiance et la décoherence du centre de masse d'un atome unique induite par l'émission spontanée. Le taux de décohérence comporte une composante locale et une composante non-locale. Ces termes ont des interprétation physique bien différentes: le terme local est lié au taux d'émission spontanée, alors que le terme non-local correspond a la qualité de l'information contenue dans le photon émis par l'atome. La contribution non-locale est associée a des interférences, et donne lieu a une oscillation du taux de décohérence qui ressemble a de la superradiance.

19 janvier 2017,
11h00

J.F. Denisse (ex salle de l'Atelier) (Paris)

Generation of a time-scale steered by an optical clock

Hidekazu Hachisu

National Institute of Information and Communications Technology

Optical clocks have recently surpassed the best microwave standards in accuracy as well as stability, although the continuous long-term operation of optical clocks for the time keeping is still a difficult task since we need to stabilize nearly ten laser frequencies including a stable probe laser. Nevertheless, building a time scale using optical clocks is definitely attractive. The strong point is the high stability of optical clocks which is more than an order of magnitude superior to fountain-based microwave standards.
The frequency of the hydrogen maser (HM), which is commonly employed as the source oscillator of a time scale, can be estimated in a few hours with reference to an optically-generated microwave from an optical clock. Intermittent operation of an optical clock and steering of the HM frequency according to the measurement result may realize a time scale with stability similar to Universal Coordinated Time (UTC). To investigate such possibility of the “optically steered” time scale, we generated a real signal of the time scale during the recent half year (Apr – Sep, 2016). Once in a week, a strontium lattice clock was operated for 104 second, and the HM frequency is accurately estimated and steered with reference to the measurement result. The optically steered time scale is compared to UTC, which will be discussed in the presentation.
The data successfully obtained for six months also allows us to investigate how often we need to operate the optical clock, or how stable the source oscillator needs to be. These points will be also discussed in the presentation. Our theoretical and experimental analysis indicates that the highly stable HMs available in our institute require infrequent operations only once in two weeks in order to keep the precision of a few ns level against an ideal time scale based on the SI second.

26 janvier 2017,
11h00

Danjon (Paris)

Brillouin microlasers and optical frequency comb generation based on WGM microresonators

Changlei Guo

Whispering gallery mode (WGM) optical microcavity is an optical microresonator with circular structure, where photons travel around its inner wall by all reflection. Benefiting from the low material loss, radiation loss and scattering loss of the cavity, WGM microresonators, in particular, the surface tension induced microspheres or microsphere-like ones possess ultrahigh quality factors. This ultrahigh quality factor together with its intrinsic low mode volume would greatly enhance the interaction between light and matter, which in turn is very beneficial to nonlinear optics. In this talk, I will specially focus on Brillouin microlasers and optical frequency comb (OFC) generation with the help of stimulated Brillouin scattering (SBS) or four-wave-mixing (FWM) in WGM microresonators. In the part of Brillouin microlasers, I will introduce the observation of SBS in silica microspheres with an ultralow threshold (as low as 8 µW), and the first observation of SBS in tellurite microspheres. In the part of OFC generation, I will talk about how to generate OFCs from a fiber-ring/microresonator system, and then I will introduce a "superoscillator model" to describe the phase-locked comb structure in the frequency domain. In addition, some applications of the Brillouin microlasers and microresonator-based OFCs will be talked, e. g. the generation of microwave signals and ultrashort pulses. This talk includes most of my research work during my doctoral student career, which were mainly finished at Xiamen University, China and partially at National Physical Laboratory, the United Kingdom.

1er février 2017,
11h00

J.F. Denisse (ex salle de l'Atelier) (Paris)

Scope and process of the ESA programme for Science in the Space Environment

Olivier Minster

European Space Agency

The ESA activities in the field of Sciences in the Space Environment (SciSpacE element of the Human Spaceflight and Robotic Exploration program) build up on three decades of experience with studying humans and living organisms and developing and operating physics instruments on various platforms on the ground and in space.
Most research projects are defined by International Topical Teams supported by ESA in coordination with other international partners. Selected projects are implemented within the resources available to ESA or in a shared mode with other international partners involved in the projects.
The scientific communities involved in SciSpacE total about 1500 individual scientists backing 150 projects or research programs. They established roadmaps for using ISS in the years to come and also the perspectives anticipated beyond the ISS era for the broad range of topics covered, namely:
· Ultraprecise cold atom sensors, quantum information and high energy particles
· Soft Matter
· Two-phase heat transfer
· Advanced material processing
· Astrobiology
· Biology under non-earth gravity conditions
· Supporting life in hostile environments
· The human body under conditions: adaptation and countermeasures
· Psychological and neurosensory adaptations to reduced gravity, isolation and confinement
In building and developing this program, ESA has maintained high the international cooperation spirit that prevails in space research and with ISS in particular. Most ISS projects are implemented in close cooperation with Roscosmos, NASA and/or JAXA in a cooperative manner. The International Topical Teams are also the natural cradle of cooperation with scientists from other countries, including naturally China and Korea.
The commonalities of topics in the ESA and China programs have been identified and a Joined Call is prepared seeking integration of projects and full exploitation of possible synergies between the program to the mutual benefit of all.
The perspectives for international cooperative projects to perform research on various space platforms are thus consolidating and ESA intends to assertively promote and support further this approach.

2 février 2017,
11h00

J. F. Denise (ex salle de l'Atelier) (Paris)

Practical Quantum Current Standard

Wilfrid Poirier

LNE

In a very near future it is planned to base the International System of units (SI) on seven defining constants, among which are the Planck constant h and the elementary charge e. This modernization will allow the SI conform realizations of the electrical units, the volt and the ohm, from the Josephson effect and the quantum Hall effect, with unprecedented low uncertainties only limited by their implementation. This will benefit to measurements. Another advantage is that the ampere, once defined from e, can be realized using quantum effects, either by using single electron tunnelling devices or by applying directly Ohm’s law to the quantum voltage and resistance standards.
In this context we have developed a novel programmable quantum current generator (PQCG) by applying Ohm’s law in an original circuit [3] combining the Josephson voltage and quantum Hall resistance standards with a highly-accurate superconducting amplifier. We have demonstrated that currents generated in the milliampere are quantized in terms of efJ (fJ is the Josephson frequency) within one part in 10^8 [1]. Able to deliver currents down to the microampere range with such accuracies, the PQCG can be used to efficiently calibrate digital ammeters. Beyond, it brings a novel direct realization of the future definition of the ampere from the elementary charge with an uncertainty at the level of 1 part in 10^8 in the new SI. It therefore competes seriously with the electron pumps reaching only 2 parts in 10^7 at 90 pA [2] at the expense of big research efforts over the last two decades.
This research can constitute a first step towards new applications in metrology: an AC current quantum standard, a quantum ammeter and even a compact quantum calibrator (voltage, resistance, current) if combining the Josephson standard with a graphene-based resistance standard operating in relaxed experimental conditions [3,4].
[1] J. Brun-Picard et al, Phys. Rev. X 6, 041051 (2016).
[2] F. Stein et al, Appl. Phys. Lett. 107, 103501 (2014).
[3] F. Lafont et al, Nat. Commun. 6, 6805 (2015).
[4] R. Ribeiro-Palau et al, Nat. Nanotech. 10, 965 (2015).

16 février 2017,
11h00

J.F. Denisse (ex salle de l'Atelier) (Paris)

Control of few-body resonant interactions in a cold Rydberg gas and 2-electron systems

Patrick Cheinet

LAC

After an introduction on Rydberg atom physics I will briefly remind our oldest results on a 4-body resonant interaction in a gas of cold Rydberg atoms of cesium. I will then present in details our latest results on a general few-body interaction scheme and explain possible applications. I will finish by presenting our new experiment on ytterbium atoms which aims at using their 2 valence electrons to expand the possible experimental tools in the study of cold Rydberg gases.

23 février 2017,
11h00

J.F. Denisse (ex salle de l'Atelier) (Paris)

Quantum clocks using composite laser-pulses spectroscopy

Thomas Zanon-Willette

LERMA

A new class of optical clocks is actively developed based on very narrow atomic transitions interrogated by composite pulses spectroscopy for robust compensation of laser probe-induced frequency-shifts below a fractional frequency change of 10^-18.
But in presence of radiative corrections due to decoherence and relaxation by spontaneous emission, the search for an absolute interrogation protocol where these probe-induced frequency-shifts are totally canceled, even for relatively important variations of experimental parameters, still remains open.
During the first part of the talk, I will briefly review well known techniques using laser pulsed spectroscopy in modern frequency standards based on neutral atoms and single trapped ion.
NMR composite pulses techniques applied in quantum information will be then quickly overviewed suggesting a possible extension to the time and frequency metrology domain.
Some new laser interrogation protocols called Hyper-Ramsey, and Modified Hyper-Ramsey, inspired by the NMR approach, will be devised to strongly reduce probe-induced frequency-shifts for ultra-narrow optical E3 transitions in ions and doubly-forbidden transitions in bosons. Two recent successful experimental applications from PTB and NPL groups will be reviewed.
The second part will be then focused on the analytical derivation of a multi-composite generalized Hyper-Ramsey (GHR) resonance with a clock frequency-shift including dissipative processes (decoherence and spontaneous emission) to characterize clock performances.
Finally, a universal interrogation scheme for fermionic and bosonic clock resonances will emerge from our computation to eliminate laser probe-induced frequency-shifts at all orders using a combination of +/-pi/4 and +/-3pi/4 phase-modulated GHR resonances interleaved by a population transfer between clock states.
This ultra-robust frequency measurement protocol might be extended to magic-wave induced transitions and magnetically induced spectroscopy, atomic interferometry, molecular frequency metrology and mass spectrometry.

2 mars 2017,
11h00

Danjon (Paris)

Ionization of metastable neon with strong-field pulsed laser radiation

James Calvert

LNE-SYRTE

Current pulsed laser systems are capable of generating laser intensities upward of 10^16W/cm^2. When matter interacts with laser radiation at these intensities, a variety of nonlinear effects can be observed, such as higher harmonic generation, above-threshold ionization and multiple ionization processes. Current understanding of these effects is through the Corkum three-step model, in which a valence electron undergoes tunneling ionization from its parent atom, is driven in the oscillating laser field and returns towards the parent ion, sometimes on a collisional trajectory. Until recently, the tunnel ionization process was typically modelled using the semi-classical Ammosov-Delone-Krainov (ADK) approach in which the strong field approximation is applied to provide an ionization rate for an atom in a given electric field, with a given ionization potential defined by the electronic state of the target atom. This approach breaks down in the limit of low ionization potentials (<10eV), where over-the-barrier ionization becomes the prevalent ionization mechanism, which in turn affects the initial state of the free electron, having flow on effects in the three state model. This work examines the strong-field ionization of the metastable 3P2 state of neon (Ne*), an atom with an ionization potential of 5.1eV, with the aim to aid in characterizing the initial ionization process of the three step model and provide insight into ionization processes. In particular, it is shown that computationally expensive TDSE solutions provide a more accurate comparison to experimental data than ADK modelling. It is also shown that the spin state of the target atom has an unexplained effect on the ionization rate, with an ionization yield difference of 16% between the ms = +1/2 and ms = -1/2 states. An examination of the transverse electron momentum from electrons released by Ne* and Ar reveals different momentum distributions for circularly polarized ionization radiation. This indicates that the strong field approximation is not applicable for atomic targets with low ionization potentials.

9 mars 2017,
11h00

J.F. Denisse (ex salle de l'Atelier) (Paris)

La gravimétrie marine : les enjeux technologiques et scientifiques

Marie-Françoise Lequentrec-Lalancette

SHOM

La gravimétrie marine englobe à la fois les techniques d’acquisition des mesures et les études ayant pour objet la connaissance du champ de gravité océanique et son interprétation. Les océans représentent environ 70% de la surface de la Terre et pourtant paradoxalement nous n’en connaissons précisément que 5 à 10%. Les modèles océaniques globaux du champ de gravité ont une résolution qui atteint au mieux cinq kilomètres. Quant à la géologie des océans, les modèles globaux restent à des résolutions très faibles de l’ordre du degré. La mesure et l’étude du champ de gravité sur les océans ont été initiées après la deuxième guerre mondiale à bord de bateaux hydro-océanographiques par les premières campagnes d’exploration notamment pour établir et confirmer le modèle dynamique de la tectonique des plaques. Puis la connaissance gravimétrique globale s’est largement développée grâce à l’avènement des satellites altimétriques à la fin des années 70. Ils ont permis un accès aux moyennes longueurs d’onde du champ de gravité intéressantes pour l’étude des processus géodynamiques. Enfin les satellites GRACE et GOCE ont permis de consolider la connaissance des grandes longueurs d’onde du champ de gravité. Dans cette présentation nous aborderons la gravimétrie marine sous l’aspect des capteurs et de leur évolution et sous l’aspect scientifique en donnant des exemples de travaux marins et sous-marins.

10 mars 2017,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Yb optical lattice clocks at 10^-18 fractional frequency level

Daniele Nicolodi

NIST, Boulder - USA

The seminar will report on recent work done with optical lattice clocks at the NIST (Boulder, USA, time and frequency division). Two Yb optical lattice clocks are developed. The work to improve and ascertain
uncertainties of these clocks to the 10^-18 fraction frequency level will be described.

16 mars 2017,
11h00

J.F. Denisse (ex salle de l'Atelier) (Paris)

Mercury optical lattice clock: from high-resolution spectroscopy to frequency ratio measurements

Maxime Favier

SYRTE

Neutral mercury is a promising candidate to build an optical lattice clock thanks to several favorable atomic properties, such as reduced sensitivity to blackbody radiation shift (BBR). However, a big challenge lies in the need for reliable cw laser sources in the UV region of the spectrum at 254 nm, 362 nm and 266 nm respectively for cooling, trapping and probing mercury atoms. In this seminar, I will present the recent improvements of the mercury optical lattice clock experiment, which allowed us to improve the uncertainty budget of the clock below the current realization of the SI second by microwave frequency standards.
I will also present the results of a measurement campaign in which we compared the mercury clock against SYRTE’s primary and secondary frequency standards, namely the dual-species atomic fountain FO2 and a Sr optical lattice clock. Finally, I will report on the implementation of new schemes involving the operationnal frequency comb, namely transfer of spectral purity to the mercury clock laser, in view of a synchroneous
"Dick-free" measurement against the strontium clock, as well as absolute calibration of the optical lattice laser for improved lattice AC Stark shift investigations.

17 mars 2017,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

The SKA Telescope(s) and applying Timing and Frequency in Radio astronomy

Luca Stringhetti and Rodrigo Olguin

SKA

The talk will be divided in two section. In the first one we will present an overview of the Square Kilometre Array SKA project, its main science goals and objectives, how it is organized, its current status, and future plan. We will present also the organization in the SKA HQ in the Jodrell Bank Observatory and the engineering office. The second part will focus the attention to one of the design element that comprises the SKA system. We will do an introduction to the timing and frequency solutions which are foreseen to be implemented in the telescope design.

23 mars 2017,
14h00

J.F. Denisse (ex salle de l'Atelier) (Paris)

Fundamentals of 5D optics for matter-wave interferometry (course 1/4)

Christian J. Bordé

SYRTE

Cours 1/4 - Attention à l'horaire

Matter-wave interferometry started with electrons and neutrons for which a
pure space-time description is sufficient in analogy with ordinary
interferometry of light waves. However, an extra phase factor is required
for these massive particles which is artificially provided by the action.
Since for these particles mass is a constant of motion the corresponding
phase is simply proportional to the proper time interval along each path.
When it comes to atoms or molecules mass varies with internal excitation and
it plays the same role as any external momentum component as a new
dynamical variable to achieve mode coupling and generate new optical paths
in an interferometer. The internal phase contributes to the overall
dephasing and is responsible for the clock term in atoms. Atomic clocks can
then be seen as genuine atom interferometers. Furthermore, it was noted
early that a "magic" compensation occurred between the action phase factor
and the residual phase in space-time originating from the splitting of end
points in equal time interferometers, suggestive of the equal paths property
in light optics. So, the action term in the phase can be reinterpreted as an
optical path if we introduce a new spatial dimension representative of the
internal motion in addition to ordinary space-time for the external motion.
Quite naturally this new dimension is chosen to be the proper interval
and the corresponding conjugate momentum is mass times the
velocity of light.

30 mars 2017,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Towards passive and active laser stabilization with strontium in an optical cavity

Jan W. Thomsen

Niels Bohr Institute, University of Copenhagen, Denmark

Today's ultra-precise and accurate atomic clocks continue to make impressive contributions to fundamental physics as well as applied science. One of the driving technologies is the phase stable clock lasers used for interrogation. Despite the tremendous success of this technology clock laser frequency noise is still one of the limiting factors preventing laboratories taking full use of the high Q-value offered by narrow atomic transitions. In this context we explore alternative methods for laser stabilization by placing cold strontium atoms in an optical cavity. One direction explores the collective non-linear phase response of the atom-cavity system [1], another direct superradiant emission of radiation from the atoms in the cavity pioneered by James K. Thompson group [2]. We report on our resent advances on laser stabilization in the two regimes and discuss clock stability limitations using these techniques. We also report on our progress towards zero dead time atomic clock based on a bright atomic beam interrogated in an optical cavity.
[1], B. T. R. Christensen, M. R. Henriksen, et al., Physical Review A, 92, 053820 (2015)
[2] M. A. Norcia, M. N. Winchester, J. R. K. Cline and J. K. Thompson, Sci. Adv. 14 e1601231 (2016)

6 avril 2017,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Cold-Atoms: A Clean system for Clocks Based on Coherent Population Trapping

Elizabeth Donley

NIST, Boulder - USA

A review of a cold-atom clock based on coherent population trapping that highlights recent progress will be presented. Improvements in the coherence of the interrogation spectrum have resulted in the generation of dark states in the cold Rb atoms with essentially 100 % transmission – evidence that decoherence in this system is negligible. This improvement in coherence has resulted in improved short-term stability at the level of 1.5 10^-11 fractional frequency stability for a one second integration period. In combination with improved interrogation schemes, the improved spectrum has also resulted in dramatically smaller light shifts and improved long-term frequency stability – with the clock typically averaging down to the level of 3 10^-13 fractional frequency stability on time scales of one hour.

13 avril 2017,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Strontium atom interferometry for precision gravity measurements

Tommaso Mazzoni

LENS

In this seminar I will present the work I have done during my PhD at LENS (Florence, Italy) about Sr atoms interferometry for gravity measurements.
The investigation for new interferometric schemes implementing atoms other than the vastly used alkali is becoming more demanding especially for dramatically improve fundamental tests in general relativity. Thanks to some peculiar characteristics, Sr atoms are good candidates for precision measurements. We investigated different interferometric schemes based on Bloch oscillations in optical lattices and Bragg pulses in free space. I will present the results of these schemes and their application to gravity measurements. I will also present the results of a fundamental test of general relativity: the Einstein Equivalence Principle and the search for spin-gravity coupling effects.

20 avril 2017,
14h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Fundamentals of 5D optics for matter-wave interferometry (course 2/4)

Christian J. Bordé

SYRTE

Cours 2/4 - Attention à l'horaire

Matter-wave interferometry started with electrons and neutrons for which a
pure space-time description is sufficient in analogy with ordinary
interferometry of light waves. However, an extra phase factor is required
for these massive particles which is artificially provided by the action.
Since for these particles mass is a constant of motion the corresponding
phase is simply proportional to the proper time interval along each path.
When it comes to atoms or molecules mass varies with internal excitation and
it plays the same role as any external momentum component as a new
dynamical variable to achieve mode coupling and generate new optical paths
in an interferometer. The internal phase contributes to the overall
dephasing and is responsible for the clock term in atoms. Atomic clocks can
then be seen as genuine atom interferometers. Furthermore, it was noted
early that a "magic" compensation occurred between the action phase factor
and the residual phase in space-time originating from the splitting of end
points in equal time interferometers, suggestive of the equal paths property
in light optics. So, the action term in the phase can be reinterpreted as an
optical path if we introduce a new spatial dimension representative of the
internal motion in addition to ordinary space-time for the external motion.
Quite naturally this new dimension is chosen to be the proper interval
and the corresponding conjugate momentum is mass times the
velocity of light.

18 mai 2017,
14h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Fundamentals of 5D optics for matter-wave interferometry (course 3/4)

Christian J. Bordé

SYRTE

Cours 3/4 - Attention à l'horaire

Matter-wave interferometry started with electrons and neutrons for which a
pure space-time description is sufficient in analogy with ordinary
interferometry of light waves. However, an extra phase factor is required
for these massive particles which is artificially provided by the action.
Since for these particles mass is a constant of motion the corresponding
phase is simply proportional to the proper time interval along each path.
When it comes to atoms or molecules mass varies with internal excitation and
it plays the same role as any external momentum component as a new
dynamical variable to achieve mode coupling and generate new optical paths
in an interferometer. The internal phase contributes to the overall
dephasing and is responsible for the clock term in atoms. Atomic clocks can
then be seen as genuine atom interferometers. Furthermore, it was noted
early that a "magic" compensation occurred between the action phase factor
and the residual phase in space-time originating from the splitting of end
points in equal time interferometers, suggestive of the equal paths property
in light optics. So, the action term in the phase can be reinterpreted as an
optical path if we introduce a new spatial dimension representative of the
internal motion in addition to ordinary space-time for the external motion.
Quite naturally this new dimension is chosen to be the proper interval
and the corresponding conjugate momentum is mass times the
velocity of light.

19 mai 2017,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Cosmological effects in the localized astronomical systems: myth or reality?

Sergei Kopeikin

University of Missouri

This talk is an attempt to answer an enigmatic question about the feasibility of measuring the impact of the cosmological expansion on the local systems bounded by local forces. We shall consider a nature of the conformal geometry and behavior of a self-gravitating isolated system, the Bohr atom (atomic clock), cavity resonator, and propagation of free electromagnetic waves in the Robertson-Walker spacetime from the point of view of a local observer. We shall comment on the nature of the, so-called, Pioneer anomaly, and argue that its nature is likely cosmological and can be used to measure the local value of the Hubble constant.

1er juin 2017,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Dark matter, variation of the fundamental constants and violation of the fundamental symmetries

Victor Flambaum

University of New South Wales, Australia

Dark matter, variation of the fundamental constants and violation of the fundamental symmetries (P, T, Lorentz, Einstein) may be searched using experiments with atomic systems including that carried out at SYRTE.

8 juin 2017,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Mesoscopic transport experiments with cold atoms

Jean-Philippe Brantut

Ecole Polytechnique Fédérale de Lausanne

Over the last decade, the level of control over cold atomic gases has improved to the point that atoms can now be used to simulate the behavior of electrons in realistic materials. I will present the progresses that we accomplished in the last years in measuring the transport properties of cold atomic gases using the Landauer two terminals setup. I will present the first observation of quantized conductance for neutral particles [1]. Its evolution as attractive interactions between particles is increased up to unitarity will be presented as pairing and superfluidity emerge [2,3]. I will then describe the most recent technical developments, namely the transposition of scanning gate microscopy in the cold atoms context, and the observation of quantum interferences in transport.
[1] S. Krinner, D. Stadler, D.Husmann, J.P. Brantut and T. Esslinger, Nature 517, 65 (2015)
[2] D. Husmann, S. Uchino, S. Krinner, M. Lebrat, T. Giamarchi, T. Esslinger and J.P. Brantut, Science 350, 1498 (2015)
[3] S. Krinner, M. Lebrat, D. Husmann, C. Grenier, J.P. Brantut and T. Esslinger, Proceedings of the National Academy of Science, 113 8144 (2016)

15 juin 2017,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Recent progresses on the SYRTE-LPL fiber link with "hybrid" architectures

Dan Xu

LNE-SYRTE

Optical fiber links in the coherent regime demonstrate outstanding capabilities to transfer optical frequency with resolution below 10^-15 to the low 10^-20 level, even on long-haul fiber links up to 1400 km [1, 2], enabling for remote optical clock comparison [3,4]. They are exploiting an active compensation of the propagation noise to achieve this ultra-high resolution. Alternative fiber noise rejection techniques were proposed recently [5], using two-way frequency comparison, as in satellite two-way Two-way T&F transfer, but at optical frequency and with guided propagation. The two-way technique is a passive rejection technique.
Using a pair of fibers connecting their two laboratory, SYRTE and LPL demonstrated that these two compensation techniques, active and passive, can be combined in a so-called "hybrid" architecture, one fiber being actively compensated and the other one being passively compensated [6]. The motivations are to check the transferred frequency with an independent technique and to study the technical and fundamental limits of coherent fiber links, while keeping a useful user output for ultra-high resolution spectroscopy experiment and clock comparisons.
In this seminar, we will show the implementation of such an hybrid fiber link that enables us to identify experimentally the contribution of the local laser and of the interferometric noise. We use here a variant called "local" two-way optical frequency comparison with self-synchronization of the data. In this setup, we are able to record at the same time the free fiber noise of the two fibers after a round-trip. In addition we will demonstrate that it is possible to use this hybrid scheme to record at the same time the forward and the backward noise on one of the two fibers. It enables us to evaluate accurately the residuals after noise rejection and the noise correlation between the 4 data sets. We will show our latest result and discuss further development on this hybrid scheme.
[1] N. Chiodo et al. "Cascaded optical fiber link using the internet network for remote clocks comparison », Optics Express 23(26),33927-33937 (2015)
[2] S. Raupach et al., "Brillouin amplification supports 1×10^20 accuracy in optical frequency transfer over 1400 km of underground fibres » S. Raupach et al. Phys. Rev. A 92, 021801(R) (2015)
[3] C. Lisdat et al. "A clock network for geodesy and fundamental science », Nature Communications 7, Article number: 12443 (2016) doi:10.1038/ncomms12443
[4] P. Delva et al. "Test of Special Relativity Using a Fiber Network of Optical Clocks », Phys. Rev. Lett. 118, 221102 (2017)
[5] C. E. Calosso et al., “ Frequency transfer via a two-way optical phase comparison on a multiplexed fiber network”, 39 (5), 1177-1180, (2014)
[6] W.-K. Lee et al. « Hybrid fiber links for accurate optical clock comparison » Appl. Phys. B (2017) 123: 161. doi:10.1007/s00340-017-6736-5

22 juin 2017,
14h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Fundamentals of 5D optics for matter-wave interferometry (course 4/4)

Christian J. Bordé

SYRTE

29 juin 2017,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Cold atom interferometry for onboard applications

Nassim Zahzam

ONERA

This seminar will present the recent progress made at ONERA in the field of cold atom interferometry which has now proven to be a very efficient technique to achieve highly sensitive and absolute inertial sensors. This kind of instruments should allow significant advances in fields such as navigation, geophysics or fundamental physics and appears also very promising candidates for future space missions. Our work focuses in particular on the realization of onboard cold atom instruments dedicated to gravity field measurements from mobile platforms such as boats, aircrafts or satellites. We will present ongoing developments at ONERA in this context and in particular recent results obtained in collaboration with SHOM concerning the elaboration of a gravity map from a ship using an absolute cold atom gravimeter. First steps toward a future space geodesy mission involving a cold atom instrument coupled to a space electrostatic accelerometer will be also presented.

6 juillet 2017,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Ultra-low noise photonic microwave generation and characterization

Romain Bouchand

LNE-SYRTE

Ultra-low phase noise microwave signals are of prime importance for a variety of applications, including radars, telecommunication and synchronization of large scientific apparatus. Photonic synthesis of those signals recently appeared promising by its ability to convey the benefits of the optics to the microwave world. In particular the synchronization of the repetition rate of an optical frequency comb to a laser stabilized on an ultra-stable cavity allows to transfer the relative frequency stability of the optical reference to a microwave signal with a drastic reduction in its absolute phase noise.
In our work, we demonstrated the photonic generation of an ultra-low noise microwave signal with a fractional frequency stability below 6.5 x 10^-16 at 1 s and a timing noise floor below 41 zs.Hz-1/2 (phase noise below -173 dBc.Hz-1 for a 12 GHz carrier). This outclasses existing sources and promises a new era for state-of-the-art microwave generation. The phase noise characterization is achieved through a heterodyne cross-correlation scheme using two optically generated low noise phase reference. This unprecedented level of purity can impact domains such as radar systems, telecommunications and time-frequency metrology. The measurement methods developed here can benefit the characterization of a broad range of signals.

7 juillet 2017,
11h00

J.-F. Denisse (ex-salle de l'Atelier) (Paris)

Frequency comparison of optical lattice clocks in RIKEN

Noriaki Ohmae

RIKEN center for Advanced Photonics - Japan

An optical lattice clock is one of the candidates for future redefinition of the second, and the accuracy of the absolute frequency measurement is limited by the realization of the current SI second. Direct comparison of optical lattice clocks with different atomic species allows the measurement of these frequency ratios with uncertainty beyond the SI second.
In RIKEN, we have developed strontium[1], ytterbium[2] and mercury[3] optical lattice clocks and have measured these frequency ratios with 10^-17 level uncertainty [4]. Instability of these frequency ratio measurement was limited by the Dick effect derived from the instability of the frequency comb because we use a single optical cavity and a comb which is used for stability transfer of this cavity to all the clocks. To improve the instability due to the comb, we have developed a new Er-fiber comb which has a single output port with uniformly-broadened and octave-spanning optical spectrum to link all the clock frequencies with 10^-17 instability at 1 sec[5]. This comb also utilizes all-polarization maintaining architecture for robust operation. In this seminar, I will show our recent researches in RIKEN.
[1] I. Ushijima et al., Nature Photonics 9, 185 (2015)
[2] N. Nemitz et al., Nature Photonics 10, 258 (2016)
[3] K. Yamanaka et al., Phys. Rev. Lett. 114, 230801 (2015)
[4] M. Takamoto et al., C. R. Physique 16, 489 (2015)
[5] N. Ohmae et al., Appl. Phys. Express 10, 062503 (2017)

### Saison 2015-2016 :

3 septembre 2015,
11h00

Salle de l'atelier (Paris)

Recent development on metrological urban network & frequency comparison

Anthony Bercy

SYRTE - LPL

Optical frequency links give the possibility to disseminate an ultrastable frequency reference to many research laboratories for a wide range of applications beyond metrology. In this context, a point-to-point transfer scheme is not efficient, especially in a metropolitan area network. During the first part of my thesis, we demonstrated a simple in-line extraction of an ultrastable signal at different points along an urban optical link of 92 km, which exhibits a stability of 1.3×10-15 at 1-s integration time with a ?-1 slop, sensibly affected by long-term thermal effect (full bandwidth Pi counter & Overlapping Allan Deviation). To improve the long-term stability and feed more users at once, we developed and tested on fibers spools an improved setup with higher output power in a compact and thermalized interferometry. Moreover, this setup gives the possibility to phase lock a laser diode on the extracted signal and to feed a secondary link, which phase noise is compensated. These two setup open the way to multiple-users dissemination in Paris area.
If one focuses on optical frequency comparisons, and puts the frequency transfer aside, the setup can be drastically simplified with a two-way method. During the second part of my thesis, we demonstrated two-way frequency transfer over a 100-km telecommunication fiber network using either unidirectional or bidirectional propagation. This last one exhibits a stability of 7×10-18 at 1-s integration time and 5×10-21 at 104 s (Lambda counter & Modified Allan Deviation), thanks to the very good rejection of the fiber noise. These results open the way to accurate and high-resolution frequency comparison of optical clocks over intercontinental fiber networks.

17 septembre 2015,
11h00

Salle de l'atelier (Paris)

Observation of Breathers in an Attractive Bose Gas

Patrick Everitt

Department of Quantum Science, Australian National University, Canberra

Recent work conducted at the ANU has resulted in the first observation of matter-wave breathers—dispersionless soliton-like states with collective oscillation frequencies driven by attractive mean-field interactions. This was achieved by taking precise measurements of the width of a 85Rb condensate as a function of time in the attractive two-body interaction regime. Curiously, it was observed that the stability of these breathers in the negative scattering regime extended well beyond what is predicted by the standard Gross-Pitaevskii equation (GPE). Moreover, the predicted oscillation frequencies and dynamics of the expanded cloud disagreed with GPE predictions. It was found that the inclusion of a three-body scattering term accurately models the observed breather behaviour.

26 octobre 2015,
11h00

Salle de l'atelier (Paris)

La prochaine génération d'horloges à piège ionique ultra-stables à JPL / The next generation of ultra-stable trapped ion atomic clocks at JPL

Eric Burt

JPL

In 2009, I presented results at the Paris Observatory on our most stable clock at that time, called L9 (or LITS-9), which drifted les than 3x10-17/day. In this talk I will summarize those results and then describe the next generation of ultra-stable trapped ion clocks currently being developed at JPL under a project called L10. The design of these clocks takes advantage of several key lessons learned from L9, which I will describe in detail. I will then discuss the initial results from the L10 project, which include a signal-to-noise improvement that enables using an optical-to-microwave LO. Finally, I will discuss several applications, including a new frequency reference for the Naval Research Laboratory (NRL) in the U.S. and a reference for the Atomic Clock Ensemble in Space (ACES) ground terminal to be located at JPL.
En 2009, j’ai présenté à l’Observatoire de Paris une communication où je décrivais la performance de l’horloge L9 (ou LITS-9), notre horloge la plus stable à cette époque qui a dérivée moins de 3x10-17/jour. Dans cette conférence je résumerai les résultats de la L9 pour en établir le contexte. Ensuite, je décrirai notre prochaine génération d’horloges à piège ionique ultra-stables à JPL, désignée comme L10, qui bénéficie des apports de la L9. Je présenterai les résultats initiaux de la L10, parmi d’autres une amélioration au rapport signal-bruit qui permet l’utilisation d’un LO optique. Finalement, je discuterai plusieurs de ses applications, surtout celles qui concernent le Laboratoire de Recherche Navale (NRL) aux Etats Unis et le projet Atomic Clock Ensemble in Space (ACES).

29 octobre 2015,
11h00

Salle de l'atelier (Paris)

A simple view on the gravitational redshift and its violation

Peter Wolf

SYRTE

Following recent work (arXiv: 1509.02854) in collaboration with Luc Blanchet, I will present a simple derivation of the gravitational redshift in atomic clocks based only on energy-momentum conservation. I will demonstrate that it is intimately related to the equivalence principle (also satisfied by Newtonian gravitation) and thus can be obtained from essentially Newtonian physics. I will then recall a simple theoretical framework dating back to the 1960s and 70s to describe a possible violation of the equivalence principle (and gravitational redshift) and show how it can be used to discuss fundamental issues like the possibility of redshift tests in the field of the Sun/Moon or the relation between different types of tests of the equivalence principle.
Whilst introducing some recent results, the seminar is aimed at the non-specialist and will be at an undergraduate physics level, with (hopefully) a little participation from the audience.

3 novembre 2015,
11h00

Salle de l'atelier (Paris)

Developing Ytterbium-ion Optical Frequency Standards in India

Subhadeep De

CSIR-National Physical Laboratory

Accurate clocks has application in sophisticated technologies, e.g., positioning satellites in their orbits, high speed communication, identifying failure in power grids, GPS communication and etc. Exploring fundamental sciences, e.g., measuring temporal constancies of fundamental constants, electron-to-proton mass ratio, geodesy and etc. relies on accurate frequency standards. This wide range of applications boosts us developing an optical frequency standard in India in its national metrology lab. We choose the ultra-narrow |2S1/2; F=0, mF=0> - |2F7/2; F=3, mF=0> electric octupole transition at wavelength 467 nm of 171Yb+ for the optical frequency standards. The states associated to this clock transition has highest sensitivity for temporal variation of the fine structure constant. Hence, inter-comparison of 171Yb+ clock at this transition with other clocks that are nearly insensitive to the temporal variation of the fine structure constant will probe the underlying physics.
The experiment relies on trapping and laser cooling of a single ion and then probing the clock transition by an ultra-stable and sub-Hz linewidth laser. Currently, we are engaged in developing subcomponents for ion trapping and laser cooling. Trapping ions for a precision frequency measurement requires harmonic potential however there are always contributions from higher order multipoles. A nearly ideal quadruopole trap in end-cap geometry has been identified through numerical simulations of geometry dependent potentials. We have analyzed ion micromotions and electric quadrupole shift to optimize the electrode geometry. We have identified the voltage and frequency parameters which are required to be avoided as they cause non-linear resonances and result to ion escape. Trap geometry dependent systematic shifts, namely, electric quadrupole, second order Doppler, second order Zeeman, Stark and black body radiation, are estimated. Aiming for a clock of ? 10-17 fractional accuracy, we have figured the machining tolerance and required control of stray electric & magnetic fields, relative rf phase difference in two electrodes. With these inputs, an end cap ion trap, compensation electrodes and its ultra-high vacuum (UHV) housing is designed indigenously. The UHV chamber has two pairs of three mutually orthogonal access ports, one set for detection of micromotions along all three directions and other set for housing trap, oven, compensation electrodes, imaging and delivering laser beams. Ytterbium oven and narrow band helical resonator for delivering rf to the trap are ready to use. The experiment requires simultaneous use of five different lasers with long term frequency stability. Field Programmable Gate Array (FPGA) based all digital laser cost effective frequency stabilization system is developed in-house. Currently we are developing the optical setups for photoionization, laser cooling and fluorescence detection of the trapped ion. The entire experiment will be automated and we are engaged in developing the automation-cum-data acquisition system. Overall progress of Indian first optical frequency standards and future plans will be presented in the meeting.

12 novembre 2015,
11h00

Salle de l'atelier (Paris)

Long high finesse fiber microcavities for metrology

Konstantin Ott

LNE-SYRTE

We present the realization of millimeter long fiber coupled open Fabry-Pérot resonators with a finesse of 46.000. Deterioration of the finesse with increasing resonator length observed in previous experiments could be suppressed by advances in the CO 2 laser-based fabrication process of the fiber micro mirrors. In this way, resonator lengths up to 1.4 mm could be realized, corresponding to a free spectral range of 107 GHz and linewidths of 2.2 MHz.
Advancements in integrating these cavities in an compact atomic clock experiment will be discussed.

26 novembre 2015,
11h00

Salle de l'atelier (Paris)

Sundry Topics on Atomic Clocks

Kurt Gibble

Penn State University

I’ll discuss diverse, recent work from our group. One result is our precision measurements of s-wave quantum scattering phase shifts of ultra-cold atoms in a cesium fountain. With mrad precision, we observe a series of Feshbach resonances with variations of s-wave phase shifts approaching pi. I’ll also discuss the microwave lensing frequency shift, the recent associated controversy and a connection to recoil shifts, and some unique aspects of the microwave lensing shift of PHARAO. The distributed cavity phase (1st order Doppler) shifts of PHARAO are also significantly different than those of fountains. I will discuss those as well as our plans for a Cadmium optical lattice clock.

3 décembre 2015,
11h00

Salle de l'atelier (Paris)

Zeeman-Stern-Gerlach decelerator using a travelling wave of magnetic field & Experimental study of metastable helium-4 at low temperature

Azer Trimeche

LNE-SYRTE

In this talk, I will review about the study and implementation of a new technique of deceleration of a supersonic beam of paramagnetic particles using a co-moving progressive wave of magnetic field. This technique relies on a method of slowing based on Stern-Gerlach forces acting on a paramagnetic system in motion in the presence of a co-propagating magnetic field. This highly innovative approach has the advantage of being applicable to a wide range of species and opens up new opportunities.
I will also present some experimental study of metastable helium-4 at low temperature. The theory predicts that perfect helium crystal should remain stable down to 35 bar below the melting line. However, an inspected instability appears only 4 bars from the melting pressure. Then I will show you our new measure of the cavitation density of liquid helium-4 around 1K. A well-established equation of state for liquid helium at negative pressures converts this to the cavitation pressure which is consistent with a model taking into account the presence of quantized vortices, but disagrees with previously published experimental values of cavitation pressure.

10 décembre 2015,
11h00

Salle de l'atelier (Paris)

Alexis Bonnin

LNE-SYRTE

10 décembre 2015,
11h00

Salle de l'atelier (Paris)

Simultaneous Dual-Species Atom Interferometry

Alexis Bonnin

LNE-SYRTE

In this talk I will present the work I did during my thesis at ONERA.
In the emerging issue of testing the Equivalence Principle with cold atom inertial sensors, this thesis focuses on the realization and the characterization of a simultaneous dual-species atom interferometer (87Rb & 85Rb) which allows to measure the differential acceleration in an extremely sensitive way. The Mach-Zehnder type atom interferometer relies on the simultaneous handling of atomic wave-packets with stimulated Raman transitions. The laser system is based on the frequency doubling of a single laser source at 1560 nm. All the required laser frequencies for handling both isotopes (trapping, cooling, selection, interferometry and detection) are generated by phase modulating this source. A detailed modeling of the interferometer’s inertial responses and an analysis of a method to extract the differential phase were carried out. The differential acceleration measurement led to an atom based test of the Weak Equivalence Principle of ?(87Rb,85 Rb) = (1.3 ± 3.2) × 10?7, at the state of-the-art. The simultaneous aspect of the experiment allowed to highlight for the first time common mode vibration noise rejection with two different atomic species, a rejection factor of 50 000 being currently achieved. The current performance of the instrument exhibits a sensitivity on the differential acceleration of 1.23 × 10?7g/?Hz and a resolution of 2×10?9g for integration times lower than few hours. Finally, innovative operating modes of dual-species atom interferometers for on-board acceleration measurements are explored.

17 décembre 2015,
11h00

Salle de l'atelier (Paris)

Low Frequency Gravitational Wave Detection with Ground Based Atom Interferometer Arrays

Rémi Geiger

LNE-SYRTE

After more than 20 years of fundamental research, atom interferometers have reached sensitivity and accuracy levels competing with or beating inertial sensors based on different technologies. Atom interferometers offer interesting applications in geophysics (e.g. detection of sub-surface mass transfers), inertial sensing, metrology and tests of fundamental physics. Recently, a growing interest for the application of atom interferometry to gravitational wave detection has been drawn.
During this seminar, I will present a new detection strategy for gravitational waves (GWs) below few Hertz based on a correlated array of atom interferometers (AIs). The method allows to reject the Newtonian Noise which represents a fundamental limit to all ground based GW detectors below few Hertz, including previous AI-based concepts. Using an array of long baseline AI gradiometers yields several estimations of the Newtonian Noise, whose effect can thus be reduced via statistical averaging. Exploiting the correlation properties of the gravity acceleration noise, I will show that a 10-fold or more Newtonian Noise rejection is possible with a dedicated configuration. Considering the current developments in cold atom technology, I will show that strain sensitivities below 1×10^19 / Hz in the 0.3-3 Hz frequency band can be within reach, with a peak sensitivity of 3×10^23 /Hz at 2 Hz. The proposed configuration could extend the observation window of current detectors by a decade and fill the gap between ground-based and space-based instruments.
Proof of principle of such Newtonian Noise rejection could be performed with the Matter wave Interferometric Gravitation Antenna (MIGA) instrument, currently under realization, and which will be operated by 2018 in the Low Noise Underground Laboratory located in Rustrel, France. I will describe the MIGA consortium, the scope of the project and the recent experimental developments.

14 janvier 2016,
11h00

Salle de l'atelier (Paris)

Recent advances in Sr optical lattice clocks at SYRTE

Slawomir Bilicki

LNE-SYRTE

Optical lattice clocks are a fast developing area of research within the
field of precision frequency metrology, with applications in fundamental
physics, quantum metrology and geodesy. We have built two similar Sr
optical lattice clocks, using a variety of laser sources for the optical
lattice – a Titanium-Sapphire laser, tapered amplifiers (TA), and slave
lasers where the latter two are injected by the same ECDL master laser.
While semi-conductor sources are appealing for field applications, a
significant frequency shift, attributed to their incoherent background
light, has been identified. On the contrary, the Titanium-Sapphire laser
is shown to be systematic-free. By comparing our laser sources, we plan
to evaluate if TAs can be reliable compact lattice light sources.
The accuracy budget of the Sr2 clock is established at 4×10^-17. We used
this high accuracy clock to perform local comparisons with optical
clocks (Sr and Hg) and microwave clocks (Rb and Cs), as well as remote
comparisons with the Sr clock at PTB via a compensated optical fibre
link, and satellite comparisons with other European metrology institutes.
These comparisons have been made possible by improving the reliably of
the Sr clocks, enabling unattended operation over several days.

21 janvier 2016,
11h00

Salle rdc Bat B (Paris)

Compact atomic clock based on coherent population trapping

François Tricot

LNE-SYRTE

The wide spread of applications using the Global Navigation Satellite Systems (GNSS) increases the need for higher stability clocks of moderate volume and low consumption. This interest has raised the development of many compact atomic clocks using atomic beam, ion trapping, cold atoms or vapor cell … Towards this new generations of compact atomic clock the SYRTE is developing a clock based on coherent population trapping (CPT). The simple scheme and high performance stability make the CPT clock a good candidate for an on-board system.
During this seminar, I will briefly introduce the CPT phenomenon. Then I will report the performance obtained with our clock prototype by exploiting a double ? scheme and a Ramsey interrogation technique. This method allowed to reach the frequency stability level of 3.2x10-13 @ 1 s. By considering the previous work I will present the main frequency noise sources. Then I will address current investigations which aim to improve the performance of our clock

28 janvier 2016,
11h00

Salle de l'atelier (Paris)

On the propagation of atoms in a modulated waveguide

Satyanarayana Bade

LNE-SYRTE

Atom interferometry has enabled high precision measurements of inertial effects (rotations and accelerations). In particular, using an interferometer, the angular
velocity is measured by exploiting the Sagnac effect via a phase shift scaling linearly with the device's enclosed area (phi=(4pi E)/(hbar c^2) A.Omega). Therefore, the sensitivity of the
interferometer depends on the interrogation time. Guided atom interferometry allows relatively long interrogation times(above hundreds of ms), thereby a high rotation sensitivity. However, several challenges need to be overcome in realizing the interferometer, for instance, coherent splitting and coherent propagation along the waveguide. In this talk, a novel magnetic waveguide designed on an atom chip using the current modulation technique will be presented. The results obtained from a numerical study of the classical propagation of the atoms in the guide will be considered in detail as well as the experimental progress of the GyrAChip project.

11 février 2016,
11h00

Salle de l'atelier (Paris)

Géodésie chronométrique et tests de la relativité générale

Pacôme Delva

LNE-SYRTE

Je présenterai l'utilisation des horloges pour faire des tests de la relativité, en particulier avec les horloges atomiques des systèmes de positionnement par satellites. Un nouveau test du redshift gravitationnel est envisagé avec les satellites Galileo 5 et 6, qui ont des orbites très excentriques suite à une erreur de lancement. Les horloges atomiques sont de plus en plus stables et exactes, et nous envisageons maintenant de les utiliser comme des instruments de mesure du potentiel gravitationnel. Je présenterai plusieurs projets qui vont dans ce sens.

18 février 2016,
11h00

Salle de l'atelier (Paris)

CPT clock based on constructive polarization modulation

Enxue Yun Peter

LNE-SYRTE

In this talk, I’d like to show the possibility to implement a high performance and compact CPT clock based on the constructive polarization modulation method.
In this scheme, a bichromatic laser field with synchronous modulation of polarization and phase is applied to an atomic ensemble, the greatly enhance population of clock states and the constructiveness of the two CPT dark states, which produced successively by the alternate polarizations, allow us to observe a high contrast CPT signal. One pulse Rabi and two pulses Ramsey interaction are studied in this configuration. The impact and the optimization of the experimental parameters involved in the time sequence are reviewed. We found the behavior of CPT amplitude agrees well with the theoretical model. We also show some progresses toward the implement of a CPT atomic clock.

25 février 2016,
11h00

Salle de l'atelier (Paris)

Efficient frequency tripling of a telecom laser diode Stabilized to iodine line at 515 nm in the 10^-14 range

Charles Philippe

LNE-SYRTE

Powerful and continuous wave lasers in the infra-red to visible range are highly attractive for various space and/or terrestrial applications including fundamental research, industrial applications, etc. Furthermore, an efficient frequency stabilization to atomic/molecular reference is needed for a drastic reduction of frequency noise in many applications, and allows an accurate knowledge of the emitted radiation. This additional quality is fundamental in many cases such as long distance interferometry, including the gravitational wave detection (eLISA project), earth observations, inter-satellites optical communications, etc.
I will show you that molecular iodine represents one of the most interesting atomic references for the realization of a frequency standard in the range of telecom laser wavelength. I will describe an original frequency tripling process based on a compact C-band telecom laser diode associated to PPLN nonlinear crystals. The optical setup is fully fibred and occupies a total volume of only 4.5 liters. It delivers up to 300 mW of green radiation (@3w) with only 800 mW of fundamental power (@w) corresponding to an optical conversion efficiency P3w/Pw ~36%.
To fulfil the iodine line-stabilization purpose i use the classical frequency modulation transfer technique with two counter-propagative beams in a 20 cm long iodine cell. I will report a preliminary evaluation of the frequency stability with an Allan deviation of sy(t) = 6.10^-14 t^-1/2.

10 mars 2016,
11h00

Salle de l'atelier (Paris)

Atom interferometer for mobile gravity measurements

Christian Freier

AG QOM, Institut für Physik, Humboldt-Universitaet zu Berlin

Surface gravity variations on Earth are of great interest in geodesy, earth sciences and natural
resource exploration. Gravimeters based on light pulse atom interferometry have shown
the potential to match and exceed the sensitivity and accuracy of other state-of-the-art absolute
gravimeters. The Gravimetric Atom Interferometer (GAIN) is a transportable instrument designed
to perform gravity measurements with high sensitivity and accuracy. It is based on interfering
ensembles of laser-cooled 87Rb atoms in an atomic fountain configuration and stimulated
Raman transitions.
After discussing our setup, gravity data from two measurement campaigns carried out in
Wettzell, Germany and in Onsala, Sweden will be presented. More than 5 days of gravity recordings
were compared to superconducting- (SG) and falling corner-cube gravimeters (FCCG)
on site. Data comparisons yield a GAIN long-term stability of 5×10-11g and the absolute gravity
value agrees to (3±4)×10-9g with a simultaneously acquired FCCG result. The state-of-the-art
accuracy, improved stability compared to FCCG and continuous long-term operation enable
new applications in geodesy and related fields.
Effective control of systematic effects is essential for achieving these results. The limiting
effect is due to wave-front distortions caused by optical elements in the Raman beam path. The
current status and strategies for mitigating these and other systematics will be discussed.

24 mars 2016,
11h00

Salle de l'atelier (Paris)

A trapped atom interferometer to search for new forces: recent progress in the ForCa-G experiment

Cyrille Solaro

LNE-SYRTE

We demonstrate a trapped atom interferometer of Rb87 in a vertical optical lattice. For shallow depths of the lattice, stimulated Raman transitions can be used to induce coherent transport between adjacent Wannier-Stark states, allowing us to perform atom interferometry and to measure with very high sensitivity, shifts in the Bloch frequency. A careful control of the trapping potential and a symmetrized interferometer configuration lead to a local force sensor with a state-of-the art relative sensitivity on the Bloch frequency, and thus on the gravity acceleration, of 1.8 10^-6 at 1 s.
We recently installed a crossed dipole trap in order to increase the number of atoms per well from a few to up to about one thousand thanks to evaporative cooling. Working with much denser atomic cloud allowed reducing coupling and phase inhomogeneities in the interferometer and increasing the coherence time by a factor 4. At densities of a few 10^12cm^-3, we observe counterintuitive behavior of the symmetrized interferometer configuration. We understand this phenomenon as a subtle competition between the widely used spin-echo technique and a very general mechanism based on identical rotation effect (ISRE). In trapped atomic clocks, ISRE, originating from particle indistinguishability, can enhance the clock's coherence via the so-called spin self-rephasing mechanism, up to several tens of seconds! We propose a model that reproduces well the experimental datas and offers clear insight into this remarkable interplay between spin-echo and spin self-rephasing.

31 mars 2016,
11h00

Salle de l'atelier (Paris)

Présentation de l'application POP, Publications de l'Observatoire de Paris

Christophe Brocquet

Bibliothèque - Observatoire de Paris

Fondée sur le logiciel Publesia développé par Florence Henry pour le LESIA, POP est un projet lancé à la demande du conseil scientifique de l'Observatoire ; il vise à permettre aux chercheurs et à leurs départements de recenser leurs publications via une interface web dans un outil mutualisé. Grâce à ce recensement, on pourra mieux suivre et analyser la production scientifique de l'Observatoire. Les différents formats d'export de POP permettront d'en exporter les données consolidées afin que chercheurs et départements puissent répondre à toute demande d'évaluation ou d'appel d'offre émanant des tutelles, de l'établissement, des départements. Enfin, interrogé grâce à un web service, cet outil disséminera automatiquement les publications vers les pages web de l'établissement, des laboratoires ou des chercheurs.

21 avril 2016,
11h00

Salle de l'atelier (Paris)

Spectral Hole Burning Laser

Olivier Gobron

LNE-SYRTE

In the context of optical clocks, which need better probing lasers to reach there quantum projection noise limit, many efforts have been carried out over the past years to improve the performance of Fabry-Perot cavity stabilized cw lasers. These systems now reach a fractional frequency stability of a few 10-16 near 1s timescale. However cavity length changes due to the thermal motion of the mirror atoms pose a severe limit to this performance.
LNE-SYRTE is investigating a different approach that has recently been demonstrated to potentially achieve tenfold higher laser stabilities. In this technique, the frequency discriminator to stabilize the laser is generated by burning spectral homogenous transmission lines into the inhomogeneously broadened absorption spectrum of rare-earth ion dopants in a crystalline matrix. At cryogenic temperatures, these ions are well shielded within the host and the transition is widely decoupled from thermo-mechanical noise. This allows for homogenus transmission line-widths of 1 kHz or less. Based on this spectral hole-burning technique we are developing a laser system with a proposed fractional short term stability of less than 10-16 and a residual drift of less than 10 mHz/s. This presentation will present the progress of the experiment and the difficulties we encountered. We will report as well a new interrogation method to use spectral holes as reference to stabilize our laser.

19 mai 2016,
11h00

Salle de l'atelier (Paris)

All-fiber repetition rate stabilization of fiber lasers and ultra-low phase noise microwave applications

Kwangyun Jung

LNE-SYRTE

Femtosecond mode-locked lasers have attracted great attention for many high-precision time/frequency applications, such as optical frequency standard, low-noise microwave signal synthesis, photonic analog-to-digital conversion, and large-scale timing distribution.
Repetition rate stabilization of mode-locked lasers is a core technology for various time/frequency applications. For high performance short-term (below ~ 10 s time scale) stability, repetition rate should be locked to high quality factor (Q) RF/microwave references or optical references. For the ultimate performance, continuous-wave (CW) lasers which are stabilized to optical references such as high-Q (~1011) ultra-stable cavities (Fabry-Perot cavity) or microresonators are required.
In this presentation, I show an all-fiber-based repetition-rate stabilization method using 2.5 km fiber delay line (Q ~1010) reference that enables all-fiber-photonic generation of optical pulse trains with sub-femtosecond absolute timing jitter in 0.01 s time scale. This technique does not require for any CW laser and carrier-envelope offset frequency detection, therefore it can be applied to a wide field relatively easily and cost-effectively. This fiber delay line technique is also used for reference-source-free timing jitter measurement method of mode-locked laser oscillators and supercontinuum with ultra-high resolution.
I will also present microwave photonics applications such as ultra-low phase noise microwave generation from mode-locked Er-fiber lasers and implementation of mode-locked laser-based remote optical/RF synchronization test bed for X-ray free-electron laser (XFEL) at Pohang Accelerator Laboratory.

26 mai 2016,
11h00

Salle de l'atelier (Paris)

Laser cooled trapped ions : a tool for spectroscopy and metrology

Luca Guidoni

Laboratoire Matériaux et Phénomènes Quantiques

Trapped ions are among the physical systems that allows for an almost perfect control of
individual quantum objects [1]. This feature is routinely used in order to demonstrate and
implement quantum information technologies but has also been successfully exploited for
metrological applications [2].
I will first present the experimental tools that allow for creation, manipulation and observation of laser cooled ions [3]. I will then give an overview of recent experiments and current
challenges concerning frequency metrology based on cold ions. The last part of the seminar
will be devoted to recent results that we obtained at Laboratoire Matériaux et Phénomènes
Quantiques. These results deal with the spectroscopy of Sr+ ions that we can trap and cool
in microfabricated devices [4, 5].
[1] D. J. Wineland, Rev. Mod. Phys. 85, 1103 (2013), URL http://link.aps.org/doi/10.1103/
RevModPhys.85.1103.
[2] D. J. Wineland and D. Leibfried, Laser Physics Letters 8, 175 (2011), URL http://stacks.
iop.org/1612-202X/8/i=3/a=001.
[3] D. J. Wineland, C. Monroe, W. M. Itano, D. Leibfried, B. E. King, and D. M. Meekhof, J. Res.
Natl. Inst. Stand. Technol. 103, 259 (1998).
[4] B. Dubost, R. Dubessy, B. Szymanski, S. Guibal, J.-P. Likforman, and L. Guidoni, Phys. Rev.
A 89, 032504 (2014), URL http://link.aps.org/doi/10.1103/PhysRevA.89.032504.
[5] J.-P. Likforman, V. Tugaye, S. Guibal, and L. Guidoni, Phys. Rev. A 93, 052507 (2016), URL
http://link.aps.org/doi/10.1103/PhysRevA.93.052507.

9 juin 2016,
11h00

Salle de l'atelier (Paris)

On probing the atomic Higgs and light new physics forces

Cédric Delaunay

LAPTh

The interaction strength of the Higgs boson to the building blocks of matter, the electron and up and down quarks, are essentially unknown. Probing these coupling is an important test of the SM which could lead not only to the establishment of new physics but also to an alternative understanding of the flavor puzzle. We propose a novel approach based on isotope shift measurements in atomic clock transitions in order to probe the Higgs-to-light-fermion couplings. Assuming state-of-the-art accuracy in frequency measurements in these systems, the sensitivity of the proposed method could surpass that of the LHC experiments. The constraining power of this method on 5th forces mediated by new physics states below the GeV scale will also be discussed.

16 juin 2016,
11h00

Salle de l'atelier (Paris)

Tests de QED sous champ magnétique intense

Rémy Battesti

LNCMI-T, Université Paul Sabatier

Les champs magnétiques intenses sont un outil traditionnel pour l’étude de phénomènes physiques comme les propriétés fondamentales de la matière condensée. Lors de ce séminaire je montrerai qu’ils peuvent également être très utiles pour réaliser des tests d’électrodynamique quantique du vide ou de systèmes liés.
Après une présentation générale du sujet, je décrirai deux expériences réalisées au Laboratoire National des Champs Magnétiques Intenses de Toulouse. La première vise à mesurer la Biréfringence Magnétique du Vide (BMV) prédite au début du XXème siècle mais encore jamais observée. La seconde est une expérience visant à placer des atomes de rubidium dans des champs magnétiques intenses afin de mesurer des facteurs de Landé de l’électron dans des états liés avec des niveaux de précisions intéressants pour se confronter aux calculs de QED et/ou à mesurer le champ de façon exacte. Je présenterai les derniers résultats issus de ces deux activités.

30 juin 2016,
11h00

Salle de l'atelier (Paris)

Towards testing Bell’s inequality using atoms correlated in momentum

Almazbek Imanaliev

LNE-SYRTE

The quantum nonlocality test using a pair of metastable helium atoms entangled in momentum will be described. The protocol we came up with is inspired from the one of Rarity and Tapster with pairs of photons entangled in momentum. The essential ingredients of this protocol are the atomic pair produced by dynamical instability of the Bose-Einstein condensate in a moving optical lattice, the coherent control of the atomic pair by Bragg diffraction and the correlation measurement of the atoms in different output modes of the interferometric protocol. The experimental characterization and preparation of atomic pair and coherent control by Bragg diffraction are presented showing the proof of principle of such protocol.

7 juillet 2016,
11h00

Bat B rdc (Paris)

High-resolution spectroscopy in atoms using coherent control

Sapam Ranjita Chanu

LNE-SYRTE

Einsteins notions of reciprocity between absorption and stimulated emission
and their relationship to spontaneous emission are backbone to the quantum
theory of light-matter interactions. The study of the fundamental phenomena
of coherent interaction of light with matter (atoms) to improve the precision
measurements and techniques will be discuss. Special attention is drawn to get
the narrow subnatural electromagnetically induced transmission (EIT), electro-
magnetically induced absorption (EIA) and nonlinear magneto-optic rotation
(NMOR) caused by alkali atoms contained in a vapor cell. A detailed theoretical
treatment, using the density matrix allows to associate each of the features of the
spectra with a special physical mechanism. Many quantum phenomena related
to interferences, coherences, optical pumping etc. are studied using home-built
diode lasers in room temperature vapor cell. I will also describes laser cooling
and trapping of rubidium atoms using different techniques are discussed in close
consideration for the improvements in the precision measurements.

### Saison 2014-2015 :

11 septembre 2014,
11h00

Salle de l'atelier (Paris)

Correlation Method for Estimation of Event Timing Precision

Event Tech

Séminaire avec présentation de la société Event Tech et présentation de leurs travaux sur : "Correlation Method for Estimation of Event Timing Precision"

6 novembre 2014,
11h00

Salle de l'atelier (Paris)

Performances of independently calibrated GPS Common-View (CV) time transfer against Time Transfer by Laser Link (T2L2)

Pierre Uhrich

LNE-SYRTE

GPS Common-View (CV) is one of the most common techniques for time transfer between remote time scales. The GPS CV time transfer uncertainty is currently limited by the hardware delay determination uncertainty. I will discuss the pros and cons of two relative calibration techniques through circulation of a traveling receiver: the relative receiver calibration (RecCal), which is a classic technique, and the computation of a hardware offset on the link between the time scale distribution reference points (LinkCal), a more recent one. I will report on a relative calibration campaign organized by SYRTE, which took place in autumn 2013 between Observatoire de Paris (OP, Paris, France), Observatoire de la Côte d'Azur (OCA, Calhern, France) and Space Geodesy Facility (SGF, Herstmonceux, Great Britain). The OP traveling equipment was made of two different GPS receivers implemented in a specific design which allowed for both RecCal and LinkCal simultaneously, in order to assess the performances of both techniques. The uncertainty improvement obtained with LinkCal against RecCal is a factor between 1.2 and 1.5 depending on the links, as has been comprehensively published very recently [1].
This GPS CV calibration campaign was achieved in parallel with a Time Transfer by Laser Link (T2L2) experiment organized by OCA, which took place between the same time scales. Both time transfer techniques having been calibrated independently, the direct comparison between the two techniques on the three links shows an agreement better than 240 ps [2], which is an unprecedented metrological validation of both techniques on continental distances.
I will conclude with some perspectives on the impact of such calibrated GPS CV either against other time and frequency transfer techniques or on traceability and metrology.
[1] Rovera et al., "Link calibration against Receiver calibration: an assessment of GPS time transfer uncertainties", Metrologia 51 (2014), 476-490.
[2] Rovera et al., "A direct comparison between independently calibrated time transfer techniques: T2L2 and GPS Common-Views", Proc. of the CPEM, Rio de Janeiro, 2014.

20 novembre 2014,
11h00

Salle de l'atelier (Paris)

Equilibrium and Nonequilibrium Behaviors of 1D Bose gases

Bess Fang

LCFIO

One-dimensional quantum many-body systems exhibit peculiar and intriguing
behaviors as a consequence of the reduced dimensionality, which enhances the
effect of fluctuations and correlations. The high degree of isolation and
controllability of experiments manipulating ultra-cold atomic gases allows for
the experimental simulation of text-book models, for which many theory tools are
available for quantitative comparison. I will present instances of such efforts
carried out during my PhD thesis, namely, the studies performed to investigate
the behavior of 1D Bose gas (Lieb-Liniger gas) at equilibrium and beyond. An
overview of the toolbox available to date to characterize the equilibrium
thermodynamics of a Lieb-Liniger gas will be shown, followed by a detailed study
of the breathing mode of such a system.

27 novembre 2014,
11h00

Salle de l'atelier (Paris)

Cavity mediated cooling and squeezing of a collective atomic motion

Oxana Mishina

University of Saarbrücken

9 avril 2015,
11h00

Salle de l'atelier (Paris)

Residual clock effect in the Cold Atom gravimeter

Pierre Gillot

SYRTE

LNE-SYRTE has developed a mobile Cold Atom Gravimeter, which participates to international comparisons of absolute gravimeter. I will briefly remind the g measurement principle and present our setup which accuracy of 4*10^-8m/s^2 is under improvement as its sensitivity of 5.7*10^-8m/s^2 at 1s and 3*10^-9m/s^2 at 10000s. Then, I will focus my presentation on our last investigation : a characterization of the limits to the symmetry of the Mach Zender type atom interferometer.
Owing to the use of a symmetrization pi pulse in their laser sequences, Mach Zehnder type atom interferometers are sensitive neither to clocks shifts nor Doppler shifts, if constant, but to changes in these quantities, which makes them accurate and sensitive inertial forces sensors. We showed how Raman laser coupling inhomogeneities, arrising from the motion of the atoms in the inhomogeneous laser beams, compromises the benefit of the symmetry and restores a parasitic sensitivity to the Doppler shift. In the presence of velocity distribution asymmetries, this can lead to parasitic phase shifts that limit the accuracy and long term stability of the gravity measurement in the low 10^-9 g range.

23 avril 2015,
11h00

Salle de l'atelier (Paris)

Compact atomic clock tested in microgravity

Mehdi Langlois

SYRTE

30 avril 2015,
11h00

Salle de l'atelier (Paris)

Time domain frequency measurements

Katharina Predehl

SYRTE

Optical fiber and satellite links provide state-of-the art solutions to distribute and compare ultra low noise time and frequency generators. However, adequate frequency comparisons require a profound understanding of the setup components and their noise characteristics. The latter may strongly vary depending on the transmission scheme, local oscillator types, and last but not least the detection scheme. This tutorial will introduce to you the two common statistical measures to characterize time domain phase and frequency noise and will teach you how electronic frequency counters may alter (even spoil) your results. It aims to rise your awareness of the importance of a well understandable and unambiguous representation of your data which is particularly indispensable when different laboratories with different equipment are involved in the measurement.

21 mai 2015,
11h00

Salle de l'atelier (Paris)

Large Area Cold Atom Gyroscope

Indranil Dutta

SYRTE

In the talk I will explain how the experiment aims to push the boundaries of performance of an atom interferometer on the ground sensitive principally to rate of rotation in a particular axis. Here, atoms are trapped and launched in a fountain geometry and using laser manipulation a Mach-Zehnder interferometric structure is formed. We can achieve up to 4-pulse atom interferometry, where according the well-known Sagnac effect, the sensitivity of the interferometer to rotation is proportional to the area enclosed by the separation of the atom wave packets. The first phase is to significantly increase the interrogation time of the interferometer (800 ms) to reach an interferometric area of 11cm2. This can lead to a very long baseline measurement for ground based interferometers. We have recently obtained fruitful results with a 480ms, 4 Pulse interferometer having a sensitivity, for the rate of rotation, of 1.2 x 10-7 rad/s/Hz1/2 for an interferometric area of 2.5 cm2. The second phase of advancement is to study continuous measurement of rate of rotation (without dead time). I will present a proof of principle for this continuous method using our fountain geometry.

28 mai 2015,
11h00

Salle de l'atelier (Paris)

Détermination de la constante de Planck au moyen de la balance du watt du LNE

Matthieu Thomas

LNE

Dans l'optique d'une modification du Système international d'unités (SI) fondée sur la valeur de constantes fondamentales de la physique, le Laboratoire national de métrologie et d'essais (LNE) a développé une expérience de balance du watt de manière à participer à la redéfinition de l'unité de masse : le kilogramme. Cette unité est en effet la dernière des unités de base du SI qui repose encore sur un artefact matériel : le prototype international du kilogramme. Une bobine circulaire, plongée dans un flux magnétique radial et horizontal est le coeur du dispositif de la balance du watt. Parcourue par un courant (phase statique), il s'exerce sur elle une force de Laplace nominalement verticale qui est comparée au poids d'une masse étalon. Déplacée de manière nominalement verticale (phase dynamique), il apparaît à ses bornes une tension. Il résulte de la combinaison de ces deux étapes l'égalité d'une puissance électrique et d'une puissance mécanique virtuelles. La détermination des grandeurs électriques par comparaison à l'effet Josephson et à l'effet Hall quantique permet d'établir une relation entre une masse macroscopique et la constante de Planck. Après une dizaine d'années de développements séparés des différents éléments, de très nombreuses caractérisations et améliorations, les premiers travaux de cette thèse ont consisté en l'assemblage des sous-ensembles de la balance du watt. Nous nous sommes ensuite intéressés à l'évaluation des composantes principales d'incertitudes et notamment à celles liées aux problématiques d'alignement : en particulier l'alignement sur la verticale des faisceaux lasers des interféromètres mesurant la vitesse de la bobine, l'alignement sur l'horizontale des pivots du comparateur de forces, et enfin l'évaluation des forces de Laplace horizontales et des moments parasites s'exerçant sur la bobine et leurs influences sur la détermination de la constante de Planck. Une valeur de la constante de Planck a été déterminée à l'été 2014, qui conduit à h=6,6260688(20)E-34 Js, évaluation dont l'incertitude-type relative est 3.1E-7. Des propositions pour améliorer cette incertitude sont avancées.

4 juin 2015,
11h00

Salle de l'atelier (Paris)

Manifestations of Dark matter in atomic and astrophysical phenomena: variation of the fundamental constants

Victor Flambaum

University of New South Wales, Sydney, Autralia

The boson dark matter particles produced after Big Bang may form a Bose condensate and/or topological defects. In contrast to traditional dark matter searches, effects produced by interaction of an ordinary matter with this condensate and defects may be first power in the underlying interaction strength, which is extremely small, rather than the second power or higher.
We discuss new effects and schemes for the direct detection of dark matter, including axions, axion-like pseudoscalar particles (ALPs) and scalar particles, as well as topological defects. Specific effects produced by the particle condensates include space-time variation of the fundamental constants (fine structure constant alpha, particle masses, etc) including both slow variation (on the cosmological scale) and fast oscillations. Topological defects may also produce transient and correlated observable effects.
In addition to traditional methods to search for the variation (atomic clocks, quasar spectra, Big Bang Nucleosynthesis, etc) we discuss variations in phase shifts produced in laser/maser interferometers (such as LIGO, Virgo, GEO600 and TAMA300), changes in pulsar rotational frequencies (which may have been observed already in pulsar glitches), non-gravitational lensing of cosmic radiation and the time-delay of pulsar signals, as well as changes in the rate of Earth rotation.
Other effects of dark matter include oscillating or transient atomic electric dipole moments, precession of electron and nuclear spins about the direction of Earth’s motion through an axion/ALP condensate (the axion wind effect), and axion-mediated spin-gravity couplings.
The proposed detection methods offer sensitive probes into important, unconstrained regions of dark matter parameter spaces.
References:
[1] Y. V. Stadnik and V. V. Flambaum. Phys. Rev. D 89, 043522 (2014).
[2] B. M. Roberts, Y. V. Stadnik, V. A. Dzuba, V. V. Flambaum, N. Leefer and D. Budker. Phys. Rev. Lett. 113, 081601 (2014).
[3] Y. V. Stadnik and V. V. Flambaum. Phys. Rev. Lett. 113, 151301 (2014).
[4] B. M. Roberts, Y. V. Stadnik, V. A. Dzuba, V. V. Flambaum, N. Leefer and D. Budker. Phys. Rev. D 90, 096005 (2014).
[5] M. Pospelov, S. Pustelny, M. P. Ledbetter, D. F. Jackson Kimball, W. Gawlik, and D. Budker. Phys. Rev. Lett. 110, 021803 (2013).
[6] A. Derevianko and M. Pospelov. Nature Physics 10, 933 (2014).
[7] Y. V. Stadnik and V. V. Flambaum. arXiv:1412.7801

11 juin 2015,
11h00

Salle de l'atelier (Paris)

Introduction of NICT Space-time standards group / Frequency comparisons between optical clocks from the point of view of geodesy

Miho Fujieda and Hiroshi Takiguchi

NICT, Japan

NICT Space-time standards group is in charge of generation and dissemination of Japan Standard Time, development of atomic frequency standards, and time and frequency transfer. The activites will be introduced briefly.
/
Theoretically optical clock has a potential to measure time of 18 digit accuracy by one-second observation.
It means that optical clock will be affected by gravity just for a 1 cm height variation, because of the gravitational redshift. Therefore, when we do "frequency comparison between optical clocks in different locations", we have to know the height difference between optical clock sites 1 cm level.
In this presentation, I'd like to show the difficulty about to know the height difference 1 cm level from two parts "static earth" and "dynamic earth".

25 juin 2015,
11h00

Salle de l'atelier (Paris)

Testing CPT and Lorentz invariance with matter and gravity

Quentin G Bailey

Embry-Riddle Aeronautical University

The foundations of modern physics include the fundamental spacetime symmetries of CPT and local Lorentz invariance. In the last two decades, theorists and experimentalists have become increasingly interested in high-precision tests of CPT and Lorentz symmetry. This is largely motivated by the exciting possibility that measurable signals from an underlying unified theory of physics may include tiny violations of Lorentz and CPT symmetry. In this presentation, I discuss current and future tests of spacetime symmetry on Earth and in space.

9 juillet 2015,
11h00

Salle de l'atelier (Paris)

Mercury lattice clock: from the Lamb-Dicke spectroscopy to stable clock operation

Rinat Tyumenev

LNE-SYRTE

In this talk I will present the work that has been done on the "Mercury lattice clock" project during my PhD in SYRTE.
I will start with brief mention of the basic concepts of optical lattice clocks, speak about motivations to use mercury in optical lattice clocks and its advantages as a frequency reference. In the second part of the talk I will describe the break through that was done during my PhD and in the end present the obtained results.