The gravimeter developed at LNE-LTE is a matter-wave interferometer of cold atoms. It uses a sequence of three equally spaced two-photon light pulses, during which the phase difference of the lasers is imprinted on the atomic wave packet. One of the main terms of uncertainty in the error budget arises from distortion of the laser phase: wavefront aberrations. This seminar will present a theoretical approach and simulations to the contribution of wavefront aberrations to the measured value of gravity.

Atomic clock comparisons represent a means to characterize the consistency of optical atomic clocks as frequency references for future redefinition of the SI second and for tests of fundamental physics. In this talk I will discuss schemes aimed at improving measurement precision in clock comparisons, including recent work at also using time and frequency techniques for the realization of quantum networking

Ultra-cold atomic ensembles are a prime choice for sources in quantum sensing experiments. In the case of atom interferometry, long interrogation times are highly desirable to obtain high precision results. This requires a great control of the input states in term of size and position dynamics, as well as an efficient description of the dynamics along the different steps of the evolution time. Space provides an environment where atom clouds can float for extended times of several seconds, as well as miscibility conditions not possible on ground. However, simulating such dynamics of single species Bose-Einstein Condensates (BEC) or interacting dual species BEC mixtures presents computational challenges due to the long expansion times and centre of mass motion induced by a displacement of the atom clouds. I will present a novel theoretical framework elaborated in [A. Pichery et al., AVS Quantum Sci. 5, 044401 (2023)], which is based on re-scaled computation grids that allowed to follow the extended free dynamics of quantum mixtures in space The theoretical concepts presented are illustrated by experiments performed in the NASA Cold Atom Laboratory (CAL) aboard the International Space Station as part of the Consortium for Ultracold Atoms in Space (CUAS). This multi-user BEC machine allows the manipulation of single species BEC at its installation as well as dual-species mixtures of K and Rb after upgrades. Following this chronology, I will present techniques used to study the dynamics of single species BEC and then extend the work to the manipulation of an interacting mixture of two BECs. This includes the design of fast and robust transport protocols to move the atoms away from the atom chip with Shortcut-To-Adiabaticity protocols, and the implementation of atomic lenses using the Delta-Kick Collimation techniques to control the expansion of the atomic clouds, as illustrated in [N. Gaaloul et al., Nat. Commun. 13, 7889 (2022)]. In addition, there will be a report about the first quantum mixture experiments in space [E. Elliott et al., Nature 623, 502 (2023)], which is a first step to the preparation of dual-species atom interferometry and future tests of the Universality of Free Fall.

Anderson localization (AL), an outcome arising from interference of multiple scattering events that result in a complete halt of a wave in disordered media, is a ubiquitous fundamental phenomenon in wave propagation. It's scope includes scalar waves like electrons and ultracold atoms or polarized waves like light or more sophisticated systems like kicked rotors, in 1D, 2D and 3D traps or lattice configurations. A dilute Bose Einstein Condensate (BEC) offers a promising platform to study AL and other quantum transport phenomena in disordered optical potentials, with unrivalled precision and control. AL of atoms in 1D has been observed, quantitatively studied and well understood. In 3D, first evidence of AL is reported, but studies of the AL transition’s critical regime remain elusive due to imprecise energy spreads. A new spectroscopic scheme (RF transfer of BEC atoms from a disorder-insensitive state to a to a disorder-sensitive state) is developed and validated in our group, to tackle that bottleneck. We have refined this new method to enable us realize a long lasting goal of measuring the "mobility-edge" of the 3D Anderson transition, relying on the energy-selective population of disorder levels. We present some recent results of this quest and discuss the challenges that persist, and some ideas to address them. The outcomes serve as a test bed for the advanced theories of AL and provide better understanding of wave propagation in quantum regimes.

Abstract not available yet

Abstract expected soon

Abstract coming soon

The redefinition of the second, planned for the 29th General Conference on Weights and Measures (CGPM) in 2030, differs greatly from the 1967 transition to the cesium standard. While cesium was the clear choice then, the current challenge is to utilize that standards based on multiple different atomic transitions now clearly outperform cesium. While one option is to simply replace cesium, an alternative approach suggests using a combination of different high-performance clocks. This ensemble-based definition could enhance accuracy by averaging measurements and promote the continued development of diverse co-primary standards, encouraging robust confirmation measurements and reducing the impact of unknown physical phenomena. The seminar will present a novel and simple formulation for the ensemble definition based on the weighted arithmetic mean of multiple normalized frequencies. It will be demonstrated that this approach is mathematically equivalent to the previously discussed implementation using a geometric mean. In this reformulation, the normalization of frequencies provides defining constants with immediate physical meaning as well as decoupling of assigned weights from the frequencies of the reference transitions. A definition based on this formulation is expected to be significantly more accessible to both experts and non-specialists, enhancing understanding and facilitating broader acceptance. This approach aims to help overcome barriers to the adoption of a redefinition that effectively values all state-of-the-art atomic clocks. The work was conducted in collaboration with Nils Nemitz from the National Institute of Information and Communications Technology (NICT) in Tokyo, Japan https://arxiv.org/abs/2503.01778

The gravimeter developed at LNE-LTE is a matter-wave interferometer of cold atoms. It uses a sequence of three equally spaced two-photon light pulses, during which the phase difference of the lasers is imprinted on the atomic wave packet. One of the main terms of uncertainty in the error budget arises from distortion of the laser phase: wavefront aberrations. This seminar will present a theoretical approach and simulations to the contribution of wavefront aberrations to the measured value of gravity.

Abstract coming soon

Several projects exists of constellation or swarms of satellites using Inter-Satellite Links (ISLs) with ranging capabilities, such as Galileo second generation which will fly as soon as 2024, or scientific projects such as NOIRE, a radio telescope consisting of a swarm of around 50 satellites around the Moon. Moreover, more and more satellites in low-earth orbit (LEO) will be equipped with Galileo receivers, creating a link between Medium Earth Orbits (MEO) and LEO satellite constellations. All these will create a network of connected satellites in space, and will offer a unique opportunity for precise orbit determination, clock synchronization and other scientific applications. We have developed a new simulator to study the absolute and relative orbit determination problem using only inter-satellite range measurements. This simulator is designed to deal with different satellite constellations; applying different parametrization models (absolute or relative orbital parameters) and considering most of the physical dynamical models. The aim of this presentation is to highlight the main results of this study carried out in an ESA project in the time-period 2020-2022.

Following its deployement at the surface of Mars, the SEIS seismometer of the NASA-InSight mission recorded tens of high-frequency Martian seismic events (> 1Hz) which we analyzed to characterize the attenuation properties of the Martian lithosphere from an Earth-Moon-Mars comparison perspective. The Martian waveforms are generally depolarized and show P and S arrivals with a gradual beginning, a broad maximum and a very long coda decay. These characteristics are highly reminiscent of the seismic wavefield in the terrestrial oceanic lithosphere at high frequency (Po and So above 2Hz), where the stratification of the absorption was used to estimate the Asthenosphere-lithosphere boundary (Takeuchi et al., 2017). To constrain the attenuation properties on Mars, we modeled the energy envelopes of the Martian events using a multiple-scattering approach in which we considered a stratification of the velocity and the attenuation properties in the medium. We observed that a simple model composed of a highly scattered crust and a weakly inhomogeneous mantle is sufficient to explain Martian events. We found that the Martian crustal diffusivity ($10^{-12} \ km^{2}/s$) is similar to the estimation obtained in the lithosphere of the Atlantic Ocean ($15–60 \ km^{2}/s$, Hannemann et al. 2022), but higher than the Lunar crust value ($2 \ km^{2}/s$). The absorption attenuation results indicate that the Martian crust is globally dry $\approx 10^{-4}$ compared to the terrestrial crust $\approx 10^{-3}$. Our results suggest that the basaltic nature and the heterogeneities of the crust are the main source of the scattering in the Martian lithosphere unlike the extend of the fractures with depth observed on the Moon.

The Laser Interferometer Space Antenna (LISA) is a future ESA-led space-based observatory to explore the gravitational universe in the frequency band between $10^{-4}$ Hz and 1 Hz. LISA implements picometer-precise inter-satellite ranging to measure tiny ripples in spacetime induced by gravitational waves (GWs). However, the single-link measurements are dominated by laser frequency noise, which is about nine orders of magnitude larger than the GW signals. Therefore, in post-processing, the Time-delay Interferometry (TDI) algorithm is used to synthesize virtual equal-arm interferometers to suppress laser frequency noise. In this presentation we identify several laser frequency noise coupling channels that limit the performance of TDI. First, the on-board processing, which is used to decimate the sampling rate from tens of megahertz down to the telemetry rate of a few hertz, gives rise to laser noise residuals and thus requires careful design. Second, the post-processing delays applied in TDI are subject to interpolation and ranging errors. We study these laser and timing noise residuals analytically and perform simulations to validate the models numerically. Our findings have direct implications for the design of the LISA instrument as we identify the instrumental parameters that are essential for successful laser noise suppression and provide methods for designing appropriate filters for the on-board processing. In addition, we discuss Time-delay Interferometric Ranging (TDIR) that serves as a third ranging sensor to estimate bias-free ranges that can be used to calibrate the biases in the primary absolute ranging measurements. We present a thorough statistical study of TDIR to evaluate its performance. Therefore, we formulate the likelihood function of the interferometric data and use the Fisher information formalism to find a lower bound on the estimation variance of the inter-satellite ranges. We find that the ranging uncertainty is proportional to the inverse of the integration time and the ratio of secondary noise power, that limits the interferometric readout, to the laser noise power. To validate our findings we implement prototype TDIR pipelines and perform numerical simulations. We show that we are able to formulate optimal estimators of the unbiased range that reach the Cramér-Rao lower bound previously expressed analytically. The developed TDIR pipeline will be integrated into the ranging processing pipeline to perform consistency checks and ensure well-calibrated inter-satellite ranges.

Optical fiber technologies form the back‐bone of today’s high‐speed internet infrastructure. Optical fibers can carry light waves with encoded information enabled high-speed and voluminous data-transmission links. The emergence of high‐gain optical amplifiers in the past few decades led to the realization of optical fiber links spanning thousands of kilometers. Recent progress in the field of fiber optics led to the development of fiber‐optic phase sensitive amplifiers (PSAs) with high gain and ultra‐low noise properties making them a potential candidate for a variety of applications in communication systems. The working principle of a PSA is based on nonlinear interaction of different waves in a single mode fiber that enable conversion of pump photons from a strong laser source into signal photons leading to signal amplification. However in practice, when the fiber nonlinearity is strong, complex four‐wave mixing (FWM) interactions between different waves in the fiber can lead to generation of high‐order parasitic sidebands that influence the evolution of all the other waves inside the amplifier, and introduce extra input ports for vacuum fluctuations, leading thus to a degradation of the noise figure (NF). Therefore, it is worth investigating the basic mechanisms that govern the amplification process of a PSA, as well as the gain and noise performances of multi‐wave PSAs.

Cold atom experiments in space offer advantages like the access to ultralong free-fall times or a low vibration noise environment making them ideally suitable for atom interferometry experiments. Implementing a second atomic species allows to test fundamental principles like the universality of free fall but also studies in molecular physics or bubble traps, enhanced by the absence of gravity. However, it is a challenge to meet the requirements of space-borne experiments in terms of robustness, autonomy and reliability while offering a high performance of the atom source. In this talk I will give an overview about the status of the MAIUS-B sounding rocket payload including ground-based experiments, performance evaluation and the recent MAIUS-2 mission.

Franck Pereira Dos Santos (SYRTE): Les technologies quantiques: capteurs et mesures Florent Deleflie (IMCCE): Éphémérides : la science au service de la société

Research on light-pulse atom interferometers is motivated by the interest in accurate and long-term stable inertial measurements. Important sensitivity levers for the latter features are the extension of the interferometry time and the transfer of large numbers of photon momenta. Ultra-cold atomic ensembles are a promising resource for light-pulse interferometers considering all aforementioned aspects. We explore collimated Bose-Einstein condensates generated on atom chips as ultra-slowly expanding gas for light-pulse interferometry. I will report on the status of experiments on ground, e.g. of our future gravimeter and in free-fall facilities, such as the Bremen drop and gravitower as well as the Einstein elevator, and in space, i.e. during the last sounding rocket mission.

Sebastien Bize (SYRTE): Le role du SYRTE dans la metrologie nationale et internationale Pierre Auclair-Desrotour (IMCCE): Les marées et leurs effets astronomiques

Abstract coming soon

Marc Lilley (SYRTE): ACES/PHARAO: the home stretch to launch Jacques Fejoz (IMCCE): KAM, stabilité, diffusion : application à la mécanique céleste

impact of atmospheric turbulence on bidirectional optical links : notion of reciprocity, of correction/pre-compensation by adaptive optics, application to high precision frequency transfer, to high data rate communications and to quantum key distribution (QKD), presentation of recent experimental demonstrations and developments : FEEDELIO, VERTIGO, PICOLO, FEELINGS.

Michel Abgrall (SYRTE): Échelles de temps nationales et internationales : construction et mise à disposition Vincent Robert (IMCCE): NAROO

Abstract coming soon

In this talk, I would like to present our latest results on the 1S-3S 2-photon continuous wave spectroscopy of Deuterium atoms. I will deal with the current situation of our experiment, focusing on the analysis and some of the main systematics, and our ideas to overcome these problems in the future. And in the perspective of opening up the field of hydrogen studies, I would like to conclude my talk by introducing our new project, the observation of the gravitational quantum states (GQS) of hydrogen, within the international collaboration GRASIAN (https://grasian.eu). The GQS are formed when a mass-particle is trapped in a potential well formed on one side by the Earth gravitational potential (top confinement) and on the other side, by an atomic mirror (a flat surface placed on the bottom) that reflects the particles upwards. The mechanism behind these specular reflections of the atoms on the mirror is the well-known quantum reflection phenomenon: a very cold mass particle can be seen as a wavepacket that has a high probability of being quantum reflected as it approaches the surface and experiences a rapid and steep change in the potential close to the mirror. These GQS have been observed on ultracold neutrons more than 20 years ago, but never with atoms. Our first goal is to observe such gravitational quantum states on hydrogen, which would open the way to new great studies on ultracold hydrogen atoms.

Jerome Lodewyck (SYRTE): Horloges à réseau optique : vers une redéfinition de la seconde SI Josselin Demars (IMCCE): Occultations stellaires

Cristan Bracco (SYRTE):  Aux origines de la relativité restreinte Jerome Berthier (IMCCE): Astéroïdes binaires et plus

Sebastien Merlet (SYRTE): Metrologie et gravimetrie M. Saillenfest (IMCCE): L' axe des planetes geantes

Rodolphe LeTargat (SYRTE): Oscillateurs et mesure de frequence dans le domaine optique G. Boué (IMCCE): Exoplanetes: physique, dynamique et detection

Paul-Eric Pottie (SYRTE): Transfert optique de temps-frequence N. Rambaux (IMCCE): Sonder l' interieur des corps avec la dynamique

Abstract not available at the moment

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We will present the ongoing development of France's first cavity-enhanced high harmonic generation (HHG) source. In the time domain, the source's high repetition rate should provide sufficient statistics to reveal quantum-optical aspects of the HHG process. In the spectral domain, the production of a frequency comb in the XUV range should enable precise spectroscopy of nuclear clock transitions.

In this talk, I present the proposal of a novel experiment to search for dark matter, based on the application of an electric field inside a microwave cavity and electrometry using Rydberg atoms. I show that this kind of experiment could be extremely useful for detecting specific dark matter candidates, namely massive vector fields coupled to the photon field, more commonly known as dark photons. Such a massive vector field is a good candidate for dark matter. Using realistic experimental parameters I show that such an experiment could improve the current constraint on the coupling constant of the dark photons to Standard Model photons in the 1 to 10 $\mu$eV mass range, with the possibility of tuning the maximum sensitivity via the cavity size. The main limiting factors on the sensitivity of the experiment are the amplitude stability of the applied field and the measurement uncertainty of the electric field by the atoms.

Spacetime-symmetry breaking has been put fourth as a candidate signal of quantum gravity, and is an expected or allowed property of several theoretical proposals. This has spawned an extensive theoretical and experimental research effort in the last decades; using a generic effective-field theory approach to the symmetry breaking, strong constraints have been put on deviations from standard physics. In the gravitational sector, most results have been obtained in the linearised limit with probes such as solar-system tests, gravitational waves, and pulsars. In this talk I will present a brief overview of the theory and phenomenology of an effective-field theory used for many precision tests of the spacetime symmetries in General Relativity and the Standard Model. Following this I will show some results obtained for strong gravity and cosmology. Finally, I will show some recent early-Universe results on the imprints of spacetime-symmetry breaking on primordial gravitational waves.

ABSTRACT Reaching quantum projection noise in atomic fountains requires a low-noise ultra-stable microwave signal. The division of a high-stability optical signal in to the microwave domain by an optical frequency comb has been proven to vastly exceed the performance of any other established technology. I present our new scheme to generate a hybrid microwave, featuring both the excellent short-term frequency stability of an optical cavity and the long-term phase predictability of an H-maser. Preliminary stabilities against microwave fountains confirm its capacity to replace our 11.98 GHz cryogenic oscillator. Moreover, the referencing of an optical clock transported outside the laboratory is a requirement to ensure the accuracy of the measurements. I present two combinations of techniques, the bootstrapping of an OFC and the exploitation of an accurate 1542 nm reference or the exploitation of an laser reference on the atomic transition of the clock, in order to generate locally an accurate RF signal, even in an environment away from a metrology laboratory.

Abstract: https://syrte.obspm.fr/tfc/seminaire/abstract-SYRTE_TZW.pdf

Atom interferometers are exquisite tools for force measurements such as gravity. However, state-of-the-art such sensors use free-falling atoms and hence cannot perform purely local force measurements. Instead, we use here optically trapped atoms to perform force sensing close to the surface of a mirror and probe with unprecedented sensitivity atom-surface interactions. We start with a non-degenerate sample of ultracold Rb87 atoms, which we transport at the vicinity of a mirror with a moving optical lattice. We end up with a 3.5 µm wide atomic cloud at a tunable distance of the mirror, with a position stability of less than a micron. We then trap them in a mixed optical trap, combining a blue detuned static lattice and a red detuned progressive wave. Inside this trap, we induce laser assisted tunnelling between Wannier-Stark states with Raman laser pulses. This allows us to create a Raman Ramsey interferometer sensitive to the external force applied onto the atoms and to perform force measurements at different distances of our mirror with a sensitivity of 5e-28 N at 1s and of 5e-30 N on the long-term. We actually measure an attractive force, with a maximum strength of order of 1.4e-27 N, where the expected Casimir Polder force amounts in our conditions to 0.5e-27 N. This force in excess arises at least partially from stray electric fields produced by charges or adsorbed atoms. These parasitic forces can be precisely determined in our setup by applying controlled additional electric fields thanks to electrodes placed around the mirror. Ideally, they would be suppressed by eliminating the spurious charges and adsorbed atoms, for instance by using UV illumination or by heating the mirror. The sensitivity of our sensor opens new perspectives for precise measurements of Casimir-Polder force and other atoms-surface interactions.

Optical Lattice Clocks have progressed swiftly in the last years, and their frequency can now be controlled at the 18 significant digits level. This opens the way towards application to multiple scientific fields, and notably to Earth Sciences: as quantum sensor, these clocks present the unique feature to be sensitive to the local gravitational potential, which is not the case with any ground-based classical device. This capacity can be used to realize a cartography of the geopotential, thus complementing traditional methods based on leveling or satellites, to better constraint the knowledge of the geoid, and possibly to detect early signs of earthquakes or to accurately quantify the rise of the sea level. In the framework of the ANR-funded project ROYMAGE, SYRTE is starting the construction of a transportable ytterbium lattice clock. This instrument will be deployed in the future over the French territory, where the fiber network REFIMEVE+ (equipex) allows remote comparisons to the ~12 stationary European optical clocks. In this seminar, we present the original approach of the loading of the atoms, the specificities of the design to fight perturbing effects on the field, and the multiples challenges we are facing assembling the system.

In the presentation, I consider extending classical Support Vector Machines (SVMs) with quantum kernels and applying them to satellite data analysis. The basic idea behind quantum computation and particular use cases for application of quantum computers in the field of remote sensing will be introduced. The design and implementation of hybrid SVMs with quantum kernels is then discussed. Here, the pixels are mapped to the Hilbert space using parameterized quantum feature maps associated with quantum kernels. The parameters are optimized to maximize the kernel target alignment. The quantum kernels are selected such that they enable analysis of numerous relevant properties while being able to simulate them with classical computers on a real-life large-scale dataset. Specifically, I approach the problem of cloud detection in the multispectral satellite imagery, which is one of the pivotal steps in both on-the-ground and on-board satellite image analysis processing chains. The experiments performed over the benchmark Landsat-8 multispectral dataset reveal that the simulated hybrid SVM successfully classifies satellite images with accuracy comparable to the classical SVM with the RBF kernel for large datasets. Interestingly, the high accuracy was also observed for the simple quantum kernels, lacking quantum entanglement.

Bosonic isotopes of mercury can help circumventing limitations of the fermionic $^{199}$Hg used so far in optical lattice clocks, and they have never been probed yet. In this seminar, we will report our experimental work towards using bosonic isotopes. In particular, we will describe key modifications of our experimental setup required to enable the search for the clock transition in bosonic isotopes. We will also give a user’s view in an European clock comparison campaign using optical fiber networks and we will report on our preliminary results for $^{199}$Hg during the last March/April 2023 campaign.

We report on the development of a transportable iodine frequency stabilized laser setup, based on compact and fibered Telecom components with a high technological readiness level (TRL). This laser system is an ultra-stable frequency reference for the assembly, integration validation and tests (AIVT) of the payload of LISA mission (Laser Interferometer Space Antenna) as part of the SYRTE laboratory contribution to the French activities carried out by a consortium of several partners lead by the French Space Agency (CNES). The compact design of the whole setup will make it easily transportable and can be readily used on different sites.

ABSTRACT Trapped atomic clock on a chip improved by spin-squeezing in a relevant metrological domain

The BIPM is responsible for the calculation of the Coordinated Universal Time (UTC), its rapid solution, UTCr, and the realization of Terrestrial Time TT(BIPM). UTC is calculated each month, UTCr each week and TT(BIPM) each year. In this talk I will present the role of Primary and Secondary Frequency Standards (PSFS) in international time scale calculation, focusing on how they guarantee the long term stability and accuracy of UTC. For this purpose, the TT(BIPM) algorithm will be introduced and the latest calculation (2022) of this time scale presented.

Absolute gravity value is requested in several domain, from geophysics to metrology with the implementation of the kilogram. Since 2003, SYRTE has developed a state-of-the-art cold atom gravimeter (CAG), based on atom interferometry technics. It uses free-falling $^{87}$Rb atoms, which experience a sequence of two-photons Raman pulses driven by counter-propagating vertical lasers. The atom interferometer phase shift is proportional to g, the Earth gravity acceleration that the CAG measured with a sensitivity better than conventional state of the art absolute gravimeters ($5.7 \cdot 10^{-8} \textrm{ m} \cdot \textrm{s}^{-2}$ in 1 s of measurement, down to $5 \cdot 10^{-10} \textrm{ m} \cdot \textrm{s}^{-2}$ after 10 000 s) and more accurately ($2 \cdot 10^{-8} \textrm{ m} \cdot \textrm{s}^{-2}$). Limits are dominated by wave-front aberrations and the cold atom source initial position fluctuations. Several improvements will be made to reach the $10^{-10}$ range both in term of accuracy and stability. For this purpose, the gravimeter moved from gravimetry reference station at LNE to Observatoire de Paris in 2021. In this presentation, I will present the experiment, briefly remind its history to then focus on our current work. I will detail some biases and their evaluation and will focus specifically on the two-photon light shift. Finally, I will talk about an attempt to improve the interferometer contrast with optimal control of Raman pulses, which led us to study to the mid pulse interferometer Raman pulse, supposed to have no effect on the measurement.

Strontium optical lattice clocks (OLC) are a promising instrument for applications ranging from the redefinition of the second in the international system to geodesy and fundamental physics, for instance, dark matter detection, variation of fundamental constants, or general relativity tests. LNE-SYRTE, Observatoire de Paris operates two Sr OLCs with a systematic uncertainty on the order of $10^{-17}$, mostly limited by the inhomogeneous thermal distribution of the vacuum chamber inducing black body radiation (BBR) shift, but also by cold collisions between the atoms trapped in each site of the optical lattice. Aiming to improve the characterization of systematic effects in optical lattice clocks below $10^{-18}$, the thermal design of the new setup comprises an Ultra High Vacuum (UHV) chamber made in copper that is also placed in a primary vacuum environment. This will limit conductive and radiative exchanges between the experimental system and the laboratory, which contributes to BBR control. In adition, we propose the implementation of Laguerre-Gaussian modes (LG$_{pl}$) to shape a multi-site trap in the 1D optical lattice. Hence reducing the density of atoms, while preserving the advantages of 1D lattices such as amplified power and spatial purity of the modes, unlike 3D optical lattices or tweezers. In this seminar, we present the progress in the assembling of the new SrC clock setup, as well as the generation of LG$_{0l}$ modes with angular index $\ell$ up to 4. Trapping depths up to 39$E_r$ for an LG$_{04}$ lattice were obtained, a priori making it possible to implement LG lattices within the clock sequence.

ABSTRACT We present a commercial compact atomic clock using the isotropic light cooling of rubidium atoms, a Ramsey microwave interrogation, as well as an absorption detection. It achieved an extreme stability of $3.2 \cdot 10^{-13}$ at 1 second and $ 1 \cdot 10^{-15} $ over more than a month. These performances are good enough to tend towards an accuracy project for this system. In this presentation, I will first speak about the experiment, before getting into further details about its short-term and long-term performances. I will then talk about the characterization of a few systematic effects, such as the quadratic Zeeman effect or the microwave phase transients. I will finally talk about our current work, which consists in imaging the cold-atoms distribution, in order to reach a better understanding of its contribution to the accuracy budget of the MuClock.

Optical clocks have demonstrated uncertainties in the $10^{-18}$ region in fractional frequency. This makes them prime candidates for applications like chronometric geodesy, navigation and fundamental physics. Such applications require frequency transfer between a reference clock in a static place and a transportable one, e.g. enabling geopotential mapping over a region. It is thus necessary to develop a free-space optical link, in order to extend the current fiber link network in a flexible way. I will present the TOFU (“Transfert Optique de Fréquence Ultrastable”) project. It consists in developing a free space phase-stabilized optical link through an airborne relay, over expected distances up to ~100km. We already set up a 300m-folded link between a ground transceiver and a retroreflector carried by a balloon at CNES premises. I will present the design of this system, which includes a phase measurement and compensation unit and an optical transceiver. Following, I will show the performance and limitations of the system, that we evaluated during a measurement campaign lead in March 2023. Finally, I will describe the further technical developments in order to build an active airborne transceiver, replacing the passive retroreflector.

The evolution of atomic clock performances over the last decades has stimulated the development of novel time/frequency transfer techniques. The most matured and operational techniques aim at almost continuous clock comparisons. These transfer techniques, using fiber links or free-space links, allow for the comparison of the means of comparison with unprecedented resolution, realizing stringent tests of their accuracy and unveiling bias and perturbations that might be related to their respective environmental constraints. The fiber network REFIMEVE is a novel infrastructure that interconnects four European NMIs including SYRTE by fiber links, and about 30 academic laboratories as user. REFIMEVE is interconnected with the Italian Quantum Backbone (IQB). More fiber network for T/F metrology are expected to emerge in Europe in the upcoming years. As a national research infrastructure and in the frame of the EU policy of open data proposed by Clonets-DS, it becomes essential to design a data service to characterize the performances of the disseminated signal and to implement robust comparison procedures, available to the clock's comparison ecosystem, to the users connected physically to REFIMEVE, and to academics interested in REFIMEVE data. To meet these objectives, we are building a scientific Information System which is the purpose of this seminar. I will present the working methodology together with with some key concepts of the information systems I built. Then I will describe the current available setup. Finally, I will show its first scientific usages, from the scientific supervision of the network and show some prospects for earth science analysis.

In this research, we delve into the application of Precise Point Positioning with Integer Ambiguity Resolution (IPPP) and the operational improvements undertaken on the IPPP toolbox at the Bureau International des Poids et Mesures (BIPM). We discuss the ongoing implementation of this toolbox at the Paris Observatory (OP) and conduct a comparative analysis involving different receivers at OP. Furthermore, we scrutinize IPPP links over a 200-day duration, highlighting the challenges associated with maintaining continuous links. Additionally, we perform an 89-day comparison between IPPP and optical fiber links, evaluating their performance using various software. This study offers insights into the operational enhancements of the IPPP toolbox, its practical implementation at OP, and the outcomes of comparative assessments, shedding light on its potential applications in time and frequency transfer.

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.

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).

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.

Abstract not available

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.

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.

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.

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.

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

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

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.

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.

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

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

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).

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.

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.

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)

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.

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.

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.

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).

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.

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.

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

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

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.

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.

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