Séminaire Temps/Fréquence du SYRTE

25 janvier 2017

**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 :

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.

### 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.