Séminaire Temps/Fréquence du SYRTE

11 février 2022

**Séminaire organisé par :**

Luca Lorini (SYRTE)

Courriel - Tél. : +33 (0) 1 40 51 21 12

**Lieu :**

Le jeudi à 11h

~~ Salle de l’Atelier~~

Observatoire de Paris

77, Avenue Denfert-Rochereau

75014, Paris.

En visioconference jusqu’à

nouvel ordre (crise COVID-19)

### Prochain séminaire :

8 décembre 2022,
11h00

Salle Denisse (ex Atelier) (https://indico.obspm.fr/event/1711/)

Frequency-comb-driven atom interferometry

Cyrille Solaro

Laboratoire Kastler Brossel

ABSTRACT
Light-pulse atom interferometry, where light pulses are used as atom beam splitters, has led to extremely sensitive and accurate quantum sensors that offer many applications in fundamental physics, geosciences and inertial navigation. Until recently, light-pulse atom interferometry had only exploited continuous-wave (cw) laser sources. During this talk, I will present atom interferometers where the beam splitters are realized with pulsed lasers, or more specifically frequency-comb lasers [1]. This technique, which we demonstrated in the visible spectrum on rubidium (Rb) atoms, paves the way for extending light-pulse interferometry to other wavelengths (e.g. deep-UV to X-UV) and therefore to new species, since one can benefit from the high peak intensity of the ultrashort pulses which makes frequency conversion in non-linear media efficient.
[1] C. Solaro et al., “Atom interferometer driven by a picosecond frequency comb”, Physical Review Letters 129, 173204 (2022).

### Saison 2022 :

3 février 2022,
11h00

En visioconference (https://indico.obspm.fr/event/1322/)

Design and realization of a $^{41}$K Bose-Einstein condensate experiment to study the many-body atomic kicked rotor model

Charbel Cherfan

SYRTE

The quantum kicked rotor (QKR) is a paradigmatic model of quantum chaos displaying dynamical localization (DL), which can be mapped onto an Anderson model in momentum pace. The QKR has been widely used to investigate Anderson-like physics experimentally by using laser cooled atoms exposed to a pulsed standing wave. In the presence of interactions, while the mean-field approximation displays a destruction of DL, new theoretical studies have shown the presence of a many-body DL in the Tonks-Girardeau regime. It shows the richness of the QKR problem with interactions, and motivates the experimental study of this system. In this talk, I will present the development of an experimental setup based on telecom fiber amplifier technology for the production of $^{41}$K Bose-Einstein condensates (BEC). Useful frequencies are generated by our original laser-cooling system[1] in the telecom domain (C-band) before the power amplification and the frequency doubling steps. It thus preserves a high level of reliability for this kind of application. We also developed a frequency stabilization technique [2][3] and demonstrated its applicability in the cold atom domain, based on telecom technology, by using ro-vibrational transitions of the acetylene molecule. Finally, for the evaporative cooling in an optical dipole trap, we have built an original telecom laser system based on power control that does not require any active element in free space. In parallel with the development of the telecom laser sources, we have conceived and built the rest of the experimental system (ultra-high vacuum system, magnetic traps, electronic systems, etc). Thanks to these developments, we observed a condensate of $2 \cdot 10^5$ atoms, which will allow us to perform later experiments on the QKR model in the presence of interactions.
[1] C. Cherfan et al., Optics. Express,28 : 494-502 (2020);
[2] C. Cherfan et al., Appl. Phys. Lett, 119, 204001 (2021);
[3] C. Cherfan et al., Frontiers in Optics + Laser Science 2021, paper FM1A.3.

10 février 2022,
11h00

En visioconference (https://indico.obspm.fr/event/1323/)

Transportable optical atomic clock based on thermal atomic ensembles

Haosen Shang

LNE-SYRTE

The optical atomic clock is the most ever signal generator to provide extraordinary frequency stability and accuracy. These characteristics open the door for its huge applications not only in scientific research, such as searching for dark matter and gravitational wave detection but also in advanced technological developments, such as the redefinition of SI second and geodesy measurements. However, most of the optical atomic clocks are still restricted to be operated under laboratory circumstances, because of their huge size and complicated structures. Therefore, a transportable optical clock system attracts more and more research interests. In this talk, I will present the transportable optical atomic clock we realized based on the thermal calcium beam [1], which considers the balance between clock performance and transportability. To further mitigate the perturbation of the environmental factors on the optical local oscillator which is locked on a high finesse optical cavity, we also put forward and developed two promising approaches to acquire a compact narrow linewidth laser system that is aimed as the transportable optical local oscillator, including narrowing laser linewidth using high signal-to-noise ratio modulation transfer spectroscopy [2] and realization of microscale continuous-wave superadditive laser [3]. Finally, to solve the common problems of low atoms utilization efficiency faced byalmost all thermal atomic ensembles, we proposed a velocity-grating spectroscopy scheme that can improve the signal-to-noise ratio by 22 times at least [4], thus further reducing the quantum projection noise and frequency instability for the transportable calcium beam optical atomic clock.
[1] H. Shang, et al., Optics Express 25(24), 30459-30467 (2017).
[2] H. Shang, et al., Optics Express 28(5), 6868-6880 (2020).
[3] H. Shang, et al., In Joint Conference of the IEEE IFCS-ISAF (IEEE, 2020), pp. 1-4.
[4] H. Shang, et al., arXiv:2012.03430 (2020).

10 mars 2022,
11h00

En visioconference (https://indico.obspm.fr/event/1328/)

The Optical Cavity as a Powerful Tool in Experimental Fundamental Physics: A Look at Three Use Cases

Michael Hartman

SYRTE

The Fabry-Perot Interferometric Optical Cavity has unique characteristics compared to split-arm interferometers which make it a powerful tool in experimental physics research. In this seminar, I recount my experiences in three research groups from varying fields in fundamental physics: interferometric gravitational-wave detection, the search for vacuum birefringence of the quantum vacuum, and the search for axion-like particles as a candidate for dark matter. In each of these projects, the optical cavity plays a central role in the precision measurement of physical phenomena.

31 mars 2022,
11h00

Salle Denisse (ex Atelier) (https://indico.obspm.fr/event/1333/)

Long-lived Spin Squeezing in a Metrologically Relevant Regime: Towards a squeezed atomic clock

Jose Alberto De La Paz Espinosa

SYRTE

Abstract not available

29 avril 2022,
14h00

Amphitheatre de l'IAP (https://indico.obspm.fr/event/1381/)

Precision Metrology with Photons, Phonons and Spins: Answering Major Unsolved Problems in Physics and Advancing Translational Science

Michael Tobar

University of Western Australia

The Quantum Technologies and Dark Matter research laboratory has a rich history of
developing precision tools for both fundamental physics and industrial applications. This includes the
development and application of novel low-loss and highly sensitive resonant photonic and phononic
cavities, such as whispering gallery and re-entrant cavities, as well as photonic band gap and bulk
acoustic wave structures. These cavities have been used in a range of applications, including highly
stable low noise classical and atomic oscillators, low noise measurement systems, highly sensitivity
displacement sensors, high precision electron spin resonance and spin-wave spectroscopy, high
precision measurement of material properties and applications of low-loss quantum hybrid systems,
which are strongly coupled to form polaritons or quasi-particles. Translational applications of our
technology has included the realization of the lowest noise oscillators and systems for advance radar,
the enabling of high accuracy atomic clocks and ultra-sensitive transducers for precision gravity
measurements.
Meanwhile, there is currently a world-wide renascence to adapt precision and quantum measurement
techniques to major unsolved problems in physics. This includes the effort to discover “Beyond
Standard Model” physics, including the nature of Dark Matter, Dark Energy and the unification of
Quantum Mechanics with General Relativity to discover the unified theory of everything. Thus, the
aforementioned technology has been adapted to realize precision measurement tools and techniques
to test some of these core aspects of fundamental physics, such as searches for Lorentz invariance
violations in the photon, phonon and gravity sectors, possible variations in fundamental constants,
searches for wave-like dark matter and test of quantum gravity. This work includes: 1) Our study and
application of putative modified physical equations due to beyond standard model physics, to determine
possible new experiments: 2) An overview of our current experimental program, including status and
future directions. This includes experiments that take advantage of axion-photon coupling and axion-
spin coupling to search for axion dark matter. High acoustic Q phonon systems to search for Lorentz
violations, high frequency gravity waves, scalar dark matter and tests of quantum gravity from the
possible modification of the Heisenberg uncertainty principle.

9 juin 2022,
11h00

Salle Denisse (ex Atelier) (https://indico.obspm.fr/event/1382/)

Secure communications in quantum networks

Eleni Diamanti

LIP6 - CNRS - Sorbonne Université

Quantum technologies have the potential to improve in an unprecedented way the security and efficiency of communications in network infrastructures. We discuss the current landscape in quantum communication and cryptography, and focus in particular on recent photonic implementations, using encoding in discrete or continuous properties of light, of central quantum network protocols, enabling secret key distribution, verification of multiparty entanglement and transactions of quantum money, with security guarantees impossible to achieve with only classical resources. We also describe current challenges in this field and our efforts towards the miniaturization of the developed photonic systems, their integration into telecommunication network infrastructures, including with satellite links, as well as the practical demonstration of novel protocols featuring a quantum advantage for a wide range of tasks. These advances enrich the resources and applications of the emerging quantum networks that will play a central role in the context of future global-scale quantum-safe communications.

16 juin 2022,
11h00

Salle Denisse (ex Atelier) (https://indico.obspm.fr/event/1383/)

Optimum phase measurement in the presence of noise

Darko Zibar

Technical University of Denmark

Single frequency lasers are an indispensable tool in many areas of scientific and engineering disciplines. The laser phase noise properties directly affect the precision and accuracy of several critical measurement techniques such as high-sensitivity laser-based spectroscopy and interferometry. The magnitude of laser phase noise is also a key limiting factor in applications based on transmitting laser light over an optical fiber, such as high-capacity coherent telecommunication, quantum cryptography and distribution of reference atomic clock signals. Accurate measurement of laser phase noise is therefore a topic of great fundamental and practical importance.
Even though the scientific field of laser phase noise measurement is more than 50 years old, the state-of-the-art measurement techniques still exhibit strong limitations in terms of the measurement sensitivity and the frequency range. The implication of these limitations are that it is not possible to: (i) accurately measure the fundamental laser linewidth (Schawlow-Townes limit), (ii) measure theimpact of optical amplifier noise on signal phase - an open problem since 1962, (iii) accurately measure phase noise of ultra-narrow linewidth lasers and (iv) provide a phase noise measurement of the emerging low-power nano-lasers. Advancing phase noise measurement techniques is thus important for providing answers to some of the fundamental questions which could potentially lead to improved laser phase noise performance.
In this talk, a fundamentally novel approach for phase noise measurement is proposed, by combining a heterodyne phase measurement with advanced digital signal processing methods aided by physical models. We thereby propose a practical phase noise measurement technique with an ultimate
accuracy that surpasses the limitations of the current techniques by the several orders of magnitude. The proposed technique provides the theoretically most accurate (optimum) measurement of a laser signal phase and approaches the quantum limit. Compared to the state-of- the-art techniques, the proposed measurement technique is not limited by the measurement noise, but rather by the fundamental quantum noise associated with the laser. We show that, in contrast to common beliefs, it is possible to measure the phase noise well bellow the conventional measurement noise floor, greatly enhancing the measurement frequency range and the sensitivity. A record measurement
frequency range and the sensitivity is achieved. This allows us to finally provide an answer to a longstanding question on the impact of amplifier noise on the signal phase. The method thus holds the potential to become a reference phase noise measurement tool.
It will also shown how the proposed approach can be extended to phase noise characterization of optical frequency combs. Finally, we introduce a novel method for noise characterization of frequency combs based on Bayesian filtering and subspace tracking. The method allows for identification and decomposition of noise sources associated with the frequency comb.
The talk will be based on the following references:
1. Darko Zibar, Jens E. Pedersen, Poul Varming, Giovanni Brajato, and Francesco Da Ros, "Approaching optimum phase measurement in the presence of amplifier noise," Optica 8, 1262-1267 (2021)
2. Giovanni Brajato, Lars Lundberg, Victor Torres-Company, Magnus Karlsson, and Darko Zibar, "Bayesian filtering framework for noise characterization of frequency combs," Opt. Express 28, 13949-13964 (2020)
3. D. Zibar et al., "Highly-Sensitive Phase and Frequency Noise Measurement Technique Using Bayesian Filtering," in IEEE Photonics Technology Letters, vol. 31, no. 23, pp. 1866-1869, 1 Dec.1, 2019, doi: 10.1109/LPT.2019.2945051.

15 septembre 2022,
11h00

Salle Denisse (ex Atelier) (https://indico.obspm.fr/event/1493/)

Adaptive optics for free-space optical links

Caroline Lim

LNE-SYRTE

Optical wavelengths are an alternative to radio-frequency and are seen today as a key technology for free-space links. The use cases are various, we will focus in particular on payload data transfer from LEO satellites (downlinks), communication with GEO satellites (bidirectional links), and satellite-based quantum key distribution. On the ground segment, the use of single-mode fiber components, and thus the coupling of the propagating signal into a single-mode fiber, is often favored. However, the coupling efficiency can be strongly hampered by the turbulence-induced phase distortions and amplitude fluctuations (called “scintillation”). Adaptive optics can provide a real-time compensation of the phase distorsions and have been identified as a key solution, as illustrated in this presentation. We first show an experimental demonstration of a LEO-to-ground optical link, with single-mode fiber coupling on the ground assisted by adaptive optics, carried out in 2018. Then we present the FEEDELIO experiment, performed in 2019, and which consisted in a demonstration in a relevant environment of pre-compensation by adaptive optics for GEO bidirectional links. The discussion includes a brief focus on the impact of anisoplanatism, and on the impact of scintillation and of non-common path aberrations. Last, we present a feasibility study of satellite-to-ground quantum key distribution accounting for different turbulence conditions, and quantifying the gain possibily brought by adaptive optics to the key rate performance.

22 septembre 2022,
11h00

Salle Denisse (ex Atelier) (https://indico.obspm.fr/event/1494/)

SKAO an introduction

Aniket Hendre, Luca Stringhetti

SKAO

Part1
SKAO organisation and Project status
L. Stringhetti
Part2 :
Overview of SKAO’s Synchronisation and Timing system (SAT)
A. Hendre
Part 3
SKAO Objective
Term of Reference for Advisory Committee
L. Stringhetti

28 septembre 2022,
14h00

Salle Denisse - Attention: date et heure inhabituels (https://indico.obspm.fr/event/1590/)

Optoelectronic oscillators for high purity microwave signal generation

Oriane Lelievre

Thales Group

High purity microwave signal generation is required in various applications (RADAR systems, wideband sampling). For high frequency operations, optics offer promising solutions to generate low noise oscillators. The aim of my thesis was to provide a comprehensive phase noise model of various Optoelectronic Oscillator (OEO) configurations operating around 10 GHz, and to optimize these configurations with consideration to the overall oscillator compactness.
In this seminar, I will first detail a simple model to design single and dual loop OEO. The model predictions are compared to experimental results with excellent agreement. I will then discuss a phase noise model for active and harmonically mode locked laser and conclude with experimental investigations to optimize the phase noise of coupled OEO.
ATTENTION: DATE ET HEURE INHABITUELS

24 octobre 2022,
14h00

Salle Denisse (ex Atelier) (https://indico.obspm.fr/event/1423/)

White Rabbit PTP for NMI time and frequency dissemination

Namneet Kaur

NPL (UK)

White Rabbit Precision Time Protocol (WR-PTP/WR) is a sub-nanosecond synchronization technology developed in 2008 at CERN as an open source project involving multiple scientific laboratories and industrial partners. In 2020, WR was included as a “High Accuracy” option for the IEEE 1588-2019 PTP standard. WR exhibits impressive frequency instability performance (a few 1e-15@1 day of integration time) with traceability (< 200 ps) to UTC and greatly exploits the existing telecommunication networks. It is a highly competitive and scalable optical fiber-based alternative to the widely used Global Navigation Satellite System (GNSS) time service, for industrial and scientific applications. The talk will present the architecture of the deployed WR links, link calibration and the advancements of the technology.

17 novembre 2022,
11h00

Salle Denisse (ex Atelier) (https://indico.obspm.fr/event/1641/)

Quantum optimal control for atom interferometry in the quasi-Bragg regime

Franck Correia

SYRTE

ABSTRACT
We develop interferometry-based atomic inertial sensors robust to Doppler-type inhomogeneities by using quantum optimal control.
Efficiency of optical pulses can be drastically improved with this method on both intensity and phase of the lasers pulses to reach the targeted quantum state with the best
possible accuracy. We focus in particular on the importance of optimizing the design of phase-modulated mirror pulses throughout fidelity calculations.
Thanks to an algorithm that uses gradient ascent pulse engineering (GRAPE), the optimized phase profiles can already be experimentally implemented using an electro-optic modulator (EOM)
in the gradiometer experiment. Large momentum transfer beamsplitters in the quasi-Bragg regime are here envisioned.

24 novembre 2022,
11h00

Salle Denisse (ex Atelier) (https://indico.obspm.fr/event/1710/)

Technological Advances in Trapped Ions Systems

Vidyut Kaushal

SYRTE

Abstract:
A trapped ions system is a key element of modern quantum technology. Universal quantum computers, quantum simulators, quantum sensing, and high-precision atomic clocks are some of the key promises of this scientific breakthrough[1]. In this talk, I will present the idea of the trapped ion system as a scalable quantum processor and focus on the recent technological advances in individual control of ions in the ion traps based on shuttling architecture [2] (a quantum processor).
[1] Ehud Altman et al. PRX Quantum 2, (2021) 017003
[2] Kaushal et. al. AVS Quantum Science 2.1 (2020) p.014101

30 novembre 2022,
10h00

Salle Denisse - Attention: date et heure inhabituels (https://indico.obspm.fr/event/1732/)

Three-body problem in General Relativity

Adrien Kuntz

Scuola Normale Superiore, Pisa, Italy

ABSTRACT
Three-body systems are very common in the universe and it is likely that future gravitational-wave detectors will detect them and measure their parameters. I will introduce a new approach ("Effective Two-Body") perturbatively solving the motion of hierarchical three-body systems by relying on the existence of two expansion parameters: small velocities and large separation of the third body. I will show how this new EFT formulation allows to compute the relativistic Hamiltonian of three-body systems order-by-order, and I will present some applications to long-term evolution of three-body systems and waveform modelling

8 décembre 2022,
11h00

Salle Denisse (ex Atelier) (https://indico.obspm.fr/event/1711/)

Frequency-comb-driven atom interferometry

Cyrille Solaro

Laboratoire Kastler Brossel

ABSTRACT
Light-pulse atom interferometry, where light pulses are used as atom beam splitters, has led to extremely sensitive and accurate quantum sensors that offer many applications in fundamental physics, geosciences and inertial navigation. Until recently, light-pulse atom interferometry had only exploited continuous-wave (cw) laser sources. During this talk, I will present atom interferometers where the beam splitters are realized with pulsed lasers, or more specifically frequency-comb lasers [1]. This technique, which we demonstrated in the visible spectrum on rubidium (Rb) atoms, paves the way for extending light-pulse interferometry to other wavelengths (e.g. deep-UV to X-UV) and therefore to new species, since one can benefit from the high peak intensity of the ultrashort pulses which makes frequency conversion in non-linear media efficient.
[1] C. Solaro et al., “Atom interferometer driven by a picosecond frequency comb”, Physical Review Letters 129, 173204 (2022).

### Saison 2021 :

4 mars 2021,
11h00

En visioconference (https://indico.obspm.fr/event/1104/)

Isolated core excitation of high-orbital-quantum-number Rydberg states of ytterbium

Henri Lehec

SYRTE

Ryderg atoms offer an ideal platform for the study of long-range interacting systems. However usual techniques for imaging and cooling are unavailable in alkali Rydberg atoms. Our approach rely on the use of a two-optically-active-valence-electron atom such as ytterbium. Ionic core transitions of this atom offer new perspectives for optical manipulation in the Rydberg state. I will present work on the isolated core excitation of ultra cold ytterbium Rydberg atoms of high orbital quantum number. The extracted energy shifts and autoionization rates are in relatively good agreement with a model based on independent electrons taking into account interactions with a perturbative approach.

11 mars 2021,
11h00

En visioconference (https://indico.obspm.fr/event/1091/)

Beating the Standard Quantum Limit for the gravitational wave detector Advanced Virgo.

Angelique Lartaux

SYRTE

In the context of the improvement of the Advanced Virgo gravitational wave detector, the
quantum noise contribution to the detector noise has to be reduced in order to increase its sensitivity and consequently the observable volume of the Universe.
One of the idea to go beyond the Standard Quantum Limit is to use frequency dependent squeezed states of light. The implementation of this technique is tested on the CALVA experiment at IJCLab in the framework of the Exsqueez ANR in collaboration with LKB, IP2I and LAPP.
In this presentation, I will give the basis of gravitational wave detection, quantum noise and squeezing to present the design of the experiment done at IJCLab followed by the characterization results of the first optical systems used to produce and measure frequency independent squeezing, a first step for the obtention of frequency dependent squeezing.

18 mars 2021,
11h00

En visioconference (https://indico.obspm.fr/event/1105/)

Accurate rotation rate measurement with a cold atom gyroscope

Romain Gautier

SYRTE

As soon as the concept of matter-wave duality rose from the early development of quantum mechanics, the possibility of creating atomic interferometers has been studied. Measurement of rotation rates through the Sagnac effect, well known in optics, became possible with atomic waves around 1990. Nowadays, cold-atom gyroscopes can reach high sensitivities competing with optical Sagnac interferometers, like fiber gyroscopes. Cold-atom inertial sensors feature promising
applications in navigation, geoscience and for tests of fundamental physics.
In our experiment, we laser-cool cesium atoms to a temperature of 2.0 $\mu$K and launch
them vertically at a velocity of 5 m$\cdot$s$^{-1}$. Light pulse atom interferometry with counter propagating
Raman transitions is used to create an interferometer with a Sagnac area of 11 cm$^2$. We then detect the internal state of the atoms at the end of the interferometer using fluorescence detection.
The SYRTE cold atom gyroscope represent the state-of-the-art of atomic gyroscopes with
a long term stability$^1$ of 3$\cdot10^{-10}$ rad$\cdot$s-1. The gyroscope has been used to test new methods to reach
better sensitivity, like the possibility to work without dead time by interrogating three atomic
clouds simultaneously$^2$, allowing us to reach a sampling rate of 3.75Hz. To reach such stability,
we need to understand and minimize the systematic effects, the main one coming from the coupling of an imperfect launch velocity and a misalignment between the two Raman beams used to perform the interferometer$^3$.
In this talk I will present our work on the evaluation of the scale factor of the gyroscope and how
it allows us to test the validity of the Sagnac effect for matter waves. The phase shift induced by
Earth rotation depends on the angle between the oriented Sagnac area of the interferometer and
the geographic north. By rotating our apparatus, we are able to vary this angle, and therefore
modulate the phase shift. This allows us to perform a test of the Sagnac effect with a relative accuracy of 2$\cdot$10$^{-4}$, which represents an improvement of a factor 100 compared to previous matter
wave experiments.
1 “Interleaved Atom Interferometry for High Sensitivity Inertial Measurements” D. Savoie, M. Altorio, B. Fang, L.
A. Sidorenkov, R. Geiger, A. Landragin, Science Advances, Vol. 4, no. 12, eaau7948 (2018)
2 “Continuous Cold-Atom Inertial Sensor with 1 nrad/sec Rotation Stability” I. Dutta, D. Savoie, B. Fang, B. Venon,
C. L. Garrido Alzar, R. Geiger, and A. Landragin, Phys. Rev. Lett. 116, 183003 (2016)
3 “Accurate trajectory alignment in cold-atom interferometers with separated laser beams” M. Altorio, L. A. Sidorenkov, R. Gautier, D. Savoie, A. Landragin and R. Geiger, Phys. Rev. A 101, 033606 (2020)

1er avril 2021,
11h00

En visioconference (https://indico.obspm.fr/event/1103/)

Systematic effects on Strontium optical lattice clocks

Yannick Focault

SYRTE

The two Strontium OLC developed at SYRTE have shown uncertainty in the low $10^{-17}$, confirmed within local and international comparisons against both microwave and optical frequency reference. Improving their performance require better control and understanding of systematic effects. We present a new generation experimental chamber, under assembly and to be installed on Sr2 system, which is expected to enable a one order of magnitude reduction on the BBR uncertainty, predominant on the discussed system. We also present measurement of the AC Stark
shift of the clock transition, with an investigation dependence of the atomic polarizabilities with the polarisation of the lattice light.

8 avril 2021,
11h00

En visioconference (https://indico.obspm.fr/event/1090/)

Simultaneous comparisons of optical clocks and atomic fountain clocks using broadband TWSTFT

Franziska Riedel

SYRTE

Two-way satellite time and frequency transfer (TWSTFT) is a technique used on a regular base to compare atomic clocks and local time scales of laboratories all over the world. However, its instability is limited mainly due to the modulation bandwidth of the signal. In the framework of the EMRP project “ITOC” (International Time scales with Optical Clocks), a unique measurement campaign was carried out, exceeding these limits by using the maximum bandwidth available for this technique so far for the first time. Within this campaign, five optical clocks and six atomic fountain clocks located in INRIM, LNE-SYRTE, NPL and PTB had been compared simultaneously over a duration of 26 days. GPS Precise Point Positioning had been used in parallel as a second, independent satellite-based technique for comparison. By applying an analysis procedure taking into account gaps and correlations on the data, results in the low 10$^{-16}$ uncertainty range could be obtained.
The presentation will review the basic concept of broadband TWSTFT, show the challenges of such a campaign and give details on the data analysis.

22 avril 2021,
11h00

En visioconference (https://indico.obspm.fr/event/1092/)

Spectral Hole Burning for Ultra-stable Lasers

Shuo Zhang

SYRTE

Ultra-stable laser is an important component of optical lattice clocks which are candidates for the future redefinition of the SI second. Spectral hole burning in rare earth doped crystals can provide narrow atomic transitions based on the absorption of optical frequencies by the doping ions. Ultra-stable lasers achieved by frequency locking a laser radiation on such narrow atomic transitions are expected to exhibit lower fundamental (thermal noise induced) limits compared to traditional system utilizing high finesse Fabry-Perot cavity, due to operation at cryogenic temperature and high mechanical quality factor of the crystal, compared to the amorphous glasses typically used in conventional Fabry-Perot Cavity designs. In our laboratory, we are using the europium doped yttrium ortho-silicate crystal (Eu:YSO), at cryogenic temperature (below 4 K). We have recently reported a double heterodyne detection regime which demonstrates a detection noise compatible with 4x10$^{-16}$ fractional frequency stability at 1s, and we have effectively demonstrated laser fractional frequency stability at 1.7 x 10$^{-15}$ at 1s. We have experimentally evaluated mechanical-deformation-induced frequency shifts of the spectral holes in Eu:YSO, which allows deducing the acceleration sensitivity of the setup, and, in the future, optimizing the design of the crystal mount. We have also quantitatively studied the effect of externally applied electric fields. Furthermore, the sensitivity of the resonant frequency to temperature changes was evaluated. A special environment where the crystal is staying in a cold He gas-filled chamber was implemented. In this environment, temperature changes induce a change of He pressure applied to the crystal. Temperature changes therefore modify the resonant frequency by two processes: direct temperature-sensitivity-induced shift, and, in parallel, pressure-change-induced shift. For a “magic” pressure-temperature couple these two processes can result in a first-order global cancellation of the temperature sensitivity of the frequency of the spectral hole which we have recently shown experimentally.

10 juin 2021,
11h00

En visioconference (https://indico.obspm.fr/event/1094/)

Single-atom coupled to an ultracold gas

Quentin Bouton

SYRTE

Individual atoms immersed into a superfluid form a paradigm of quantum physics. It lies at the heart of many models exploiting the quantum nature of individual atoms to understand quantum phenomena or to open novel routes to local probing and engineering of quantum many-body systems. In the talk, I will present our approach of controlled immersion of individual, localized neutral Cesium (Cs) atoms into a Rubidium (Rb) ultra-cold bath [1].
The first part of my talk is dedicated to local probing: I will present our experimental realization of single-atom quantum probes for local thermometry based on the spin dynamic of the Cs atoms immersed into the Rb ultracold gas. By controlling microscopic atomic collisions, we map thermal information about the gas onto the quasi-spin population of the probe. Our probe is not restricted to measure temperature, but it allows sensing any mechanism affecting the total collisional energy in a spin-exchange collision such as the magnetic field, realizing also local magnetometry. In particular, I will show that having access to the dynamics of the microscopic process of motion-spin mapping allows us optimizing the information flow. Quantifying the sensitivity of our probe by the Quantum Fisher information, we find that it can outperform the steady-state limits setting the Cramér-Rao bound by roughly one order of magnitude [2].
The second part of my talk will be focused on the realization of a heat engine where the working fluid is embodied by the Cs atoms and the bath by the cloud of ultracold Rb atoms. Specifically, our engine is based on the quantum Otto cycle. Heat transfer is realized by spin-exchange collisions between the working fluid and the bath, while work is performed by changing the energy-level spacing of the engine with an external magnetic field. Thanks to the ability to follow the populations of individual atomic levels of a cesium atom in real time, we have performed precise characterization of the engine including the fluctuations of its power [3].
[1] F. Schmidt et al, Phys. Rev. Lett. 121, 130403 (2018).
[2] Q. Bouton et al., Phys. Rev. X 10, 011018 (2020).
[3] Q. Bouton, arXiv:2009.10946 (2020).

17 juin 2021,
11h00

En visioconference (https://indico.obspm.fr/event/1112/)

The Digital Revolution, also in Time and Frequency Metrology

Claudio Calosso

INRIM - Italy

Many times people are so focused on physical signals that they loose sight of the information they are really interested in. This is the heritage of the past, where processing was analog and each step necessarily implied a regeneration of the physical signals. Even now, that digital electronics is well established since decades, this forma-mentis survives and represents a real limitation in taking full advantage of digital electronics and to really extend the beneficial effects of the digital revolution to time and frequency metrology. The seminar will focus on timescales generation as a case study to show the differences between the two approaches.

1er juillet 2021,
11h00

En visioconference (https://indico.obspm.fr/event/1099/)

Oscillating dark matter: experiments and data analysis at SYRTE

Peter Wolf

SYRTE

In the standard current cosmological model cold dark matter (DM) accounts for about 23% of the energy of the universe and about 83 % of it's matter content. It is postulated in order to explain numerous astronomical and cosmological observations, and is assumed to exist e.g. in our galaxy and in our solar system. In ~2015 and the following years first publications described the possibility that dark matter fields might introduce local oscillations or transient variations of fundamental constants that could be measured by atomic clocks and/or ultrastable oscillators. I will describe some experiments and data analysis of searches for such DM at SYRTE and in collaborations involving SYRTE, that took place between 2015 and today and are partly still ongoing, unfortunately with no positive detection event so far. For the sake of keeping in time, I will concentrate on oscillating DM, and only briefly mention transient DM searches.

8 juillet 2021,
11h00

En Visioconference (https://indico.obspm.fr/event/1148/)

Gérer et ouvrir les données de recherche : enjeux et pratiques

Cécile ARÈNES

Chargée de mission Données de la recherche et Humanités numériques Bibliothèque de Sorbonne Université

Séminaire exceptionnel en langue Française sur la thématique "Open Data" dans le domaine de la recherche
Cécile ARÈNES
Chargée de mission Données de la recherche et Humanités numériques Bibliothèque de Sorbonne Université

14 octobre 2021,
11h00

En visioconference (https://indico.obspm.fr/event/1261/)

Le libre accès à l’Observatoire de Paris - Le cas spécifique de l’archive ouverte HAL

Fayard Aurélie

Bibliothèque de l’Observatoire de Paris.

La Bibliothèque de l’Observatoire de Paris a créé un portail HAL pour répondre aux attentes du MESRI et aux obligations de dépôt pour les publiants du CNRS, les porteurs de projets ANR et européens. Ce portail a déjà été alimenté avec les notices des publications des chercheurs des différents laboratoires de l’Observatoire de Paris. A ce jour, cela représente l’ensemble des publications présentes sur ADS et parues dans des revues à comité de lecture entre 2012 et 2020. Pour répondre aux recommandations du MESRI et du CNRS, la Bibliothèque de l’Observatoire de Paris souhaiterait développer avec le SYRTE sa politique de libre accès afin de faciliter le travail des chercheurs et ingénieurs du laboratoire. La collection du SYRTE dans le portail HAL de l’Observatoire comptabilise d’ores et déjà 460 documents (avec dépôt du texte intégral) et 562 notices – références bibliographiques. La bibliothèque ayant déjà mené plusieurs séances de présentation de HAL dans d'autres laboratoires propose de présenter aux membres du SYRTE le fonctionnement et les possibilités offertes par les archives ouvertes HAL. Cette presentation permettra également d’avoir un échanges sur ses aspects pratiques.
SEMINAIRE EN FRANCAIS

28 octobre 2021,
11h00

Salle Denisse (Ex salle de l'Atelier)
77 Av. Denfert Rocherau
75014 Paris (https://indico.obspm.fr/event/1242/)

Free-Space Optical link for clock comparison

Nicolas Maron

SYRTE - Equipe theorie et metrologie

The emerging generation of optical clocks holds great perspectives for fundamental physics and open up new fields of applications, such as chronometric geodesy. These clocks, reaching residual frequencies instabilities in the low $10^{-18}$, require means of comparison in the optical frequency domain. Mainly optical fiber link can reach sufficient performance, but are the limiting factor for applications in need of reconfigurable, rapidly deployable or in space links. Our work aims to demonstrate a ground-to-ground stabilized free-space optical link via an airborne relay. We are currently working on a 600 m folded free space link, achieving stability of $10^{-18}$ after 20 s of integration. I will present our link design and results as well as development perspectives toward our end goal.

4 novembre 2021,
11h00

En visioconference (https://indico.obspm.fr/event/1264/)

Time delay interferometry technique for the LISA mission

Martina Muratore

Università di Trento - Italy

LISA, the Laser Interferometer Space Antenna, is the 3rd large mission (L3) of the ESA program Cosmic Vision planned to be launched around 2034. Space-based gravitational wave observatories such as LISA have been developed for observation of sources that produce gravitational wave (GW) signals with frequencies in the mHz regime. GWs manifest themselves as a tiny fluctuation in the frequency of the laser beam measured at the phase-meter. Thus, to detect GWs with LISA we need to compete with many sources of disturbance that simulate the effect of a GW frequency modulation. Laser noise is an example of those. Therefore, one key element in the LISA data production chain is a post-processing technique called Time Delay Interferometry (TDI) aimed at suppressing the intense laser frequency noise that would completely cover the astrophysical signal. In this talk I will revisit the TDI technique for LISA and I will speak about the usage of all the possible TDI combinations we can build for the LISA science and instrument characterization.

18 novembre 2021,
11h00

Salle Denisse (Ex salle de l'Atelier)
Observatoire de Paris (https://indico.obspm.fr/event/1269/)

Quantum-Enhanced Atom Interferometry

Robin Corgier

SYRTE - Equipe theorie et metrologie

The possibility to overcome the standard quantum limit (SQL) by engineering specific quantum correlations between the atoms is attracting increasing interest in the field of atom interferometry. Recently, Bose-Einstein condensates (BECs) have been pinpointed as optimal candidates for the realization of entanglement-enhanced atom interferometers with spatially separated arms either in trapped [1] or free-fall [2] configurations. However, either due to the presence of residual interactions during the interferometer sequence or due to the fast expansion of the BEC during the state preparation, only a modest sub-SQL sensitivity gain is predicted.
To overcome these problems, we recently proposed a novel method we refer to as Delta-Kick Squeezing (DKS) [3]. This method involves the rapid action of an external trap focusing the matter-waves to significantly increase the atomic densities during a preparation stage. This method is explored in the two relevant cases of Raman or Bragg scattering light pulses. In the second case, we demonstrated the possibility to implement a non-linear readout scheme making the sub-SQL sensitivity highly robust against imperfect atom counting detection [4,5]. We predict more than 30 dB of sensitivity gain beyond the SQL, assuming realistic parameters and millions of atoms in the BEC.
References:
[1] R. Corgier, L.Pezzè and A. Smerzi, PRA 103 (2021).
Nonlinear Bragg interferometer with a trapped Bose-Einstein condensate
[2] S. S. Szigeti, S. P. Nolan, J. D. Close, and S. A. Haine, PRL 125 (2020).
High Precision quantum-enhanced gravimetry with a Bose-Einstein condensate
[3] R. Corgier, N. Gaaloul, A. Smerzi and L.Pezzè, PRL 127 (2021).
Delta-kick Squeeing
[4] E. Davis, G. Bentsen, and M. Schleier-Smith, PRL 116, 053601 (2016).
Approaching the Heisenberg limit without single-particle detection.
[5] O. Hosten, R. Krishnakumar, N. J. Engelsen, and M. A. Kasevich, Science 352 (2016).
Quantum phase magnification