Ultra-stable lasers based on spectral hole burning are a promising alternative scheme to overcome the thermal noise limitation of the traditional ultra-stable Fabry-Perot cavity scheme. In this dissertation, a Eu³⁺Y₂SiO⁵ crystal at cryogenic temperatures is used to realize narrow spectral holes as a frequency reference. A flexible and versatile multi-mode heterodyne laser probing scheme based on software defined radio is realized to achieve low detection noises.

The crystal is further cooled down to sub-kelvin temperatures to gain better thermal noise and temperature sensitivity performances. Meanwhile, some relevant spectral hole properties are characterized at this temperature regime, and some useful properties are found, which differ from theoretical predictions based on simple models.

Furthermore, a previously unobserved phenomenon, that I call “glowing”' is reported, together with preliminary analysis based on several characterization measurements, providing new insights to understand the system of Eu3+Y2SiO5 crystal.

Remarkably, the fractional frequency stability of the laser, based on the spectral hole burning scheme, has been encouragingly enhanced to 4(1)×10⁻¹⁶ at 1 s, approximately 2 times better than the previously reported results. This provides compelling evidence of the potential of the spectral hole burning approach for metrological applications.

ultra-stable laser, Eu:YSO, spectral hole, frequency metrology

Full document (EN) : TEL-04822912

Ultralight dark matter (ULDM), as a class of low mass (< 1 eV) dark matter (DM) candidates, is a compelling alternative to historically dominant models such as WIMPs and has recently gained significant attention in the scientific community. In this thesis, we study various experimental schemes for the direct detection of ULDM, both on ground and in space. More precisely, we propose a theoretical modeling of current and futuristic experiments, and we derive an estimation of their respective sensitivity.

We mainly concentrate on three distinct phenomenologies.

The first one is the coupling between a DM (1) field, known as the dark photon (DP), and electromagnetism, which induces a small electric field oscillating at the DP Compton frequency. We first propose an innovative way of detecting this small electric field by measuring the quadratic Stark shift of Rydberg atoms inside a microwave cavity, and we show that such an experiment could reach competitive constraints compared to existing laboratory experiments. Another possibility of detecting this electric field is to use a spherical mirror, which reflects it and focuses the electromagnetic power at its center of curvature, where a horn antenna is located (e.g. SHUKET experiment at CEA Saclay). We analytically investigate the effects of diffraction and mode matching in this type of experiment, and we show that the expected signal intensity can be significantly reduced compared to usual estimates. In this study, we also propose an optimization of the experimental parameters in order to increase the signal.

The second main phenomenology considered in this thesis is the oscillation of rest mass and transition frequencies of atoms and test masses. These oscillations could be produced by the non-universal coupling of standard matter with a scalar ULDM candidate (dilaton or axion-like particle). We extensively study the impact of such oscillations on various atom interferometer schemes and classical tests of the universality of free fall, and we demonstrate how these different experiments could probe unconstrained regions of the parameter space. The oscillation of rest mass could also be observed in space-based gravitational wave (GW) detectors, such as LISA, and we investigate the possibility of such detection using more realistic orbits of spacecraft compared to previous studies. In particular, using Bayesian methods, we show that LISA could disentangle scalar ULDM signals from monochromatic GWs. We also show that the small velocity of the DM wave is not resolvable for most frequencies in the LISA band, which induces a decrease in sensitivity to scalar ULDM couplings, with respect to previous studies.

 Finally, we study the effect of vacuum birefringence and dichroism induced by the coupling between axions and photons, and how it could be detected with optical cavities, fibers, and LISA. In particular, we show that a slight modification of LISA’s optical benches would make LISA the most sensitive experiment to the axion-photon coupling at low axion masses.

ultralight dark matter, axion, dilaton, dark photon, quantum sensors, atomic clock, atom interferometry, optical interferometry, LISA, equivalence principle, fundamental physics

Full document (EN) : TEL-04750272

Depuis le début du 20^e siècle, les observations géodésiques permettent de suivre les variations de la rotation de la Terre et ainsi d’étudier les effets dynamiques externes et internes à l’origine de ces variations. Les années 1980 ont vu les toutes premières tentatives d’estimation des variations sub-diurnes de la rotation terrestre grâce aux sessions intensives VLBI. Elles ont été suivies par des campagnes d’observation continue (CONT) du réseau VLBI puis les traitements des observations du GNSS. Alors que la capacité du réseau VLBI à estimer la variation subdiurne de la rotation de la Terre est encore limitée par la fréquence insuffisante des sessions d’observation régulières, le GNSS est avantagé par un réseau plus étendu et de ses observations beaucoup plus fréquentes.

Dans ce travail, nous utilisons les données de la constellation américaine GPS et de la constellation européenne Galileo couvrant la période 2017 à 2022 pour déterminer à la fois des solutions mono-constellation et des solutions multi-GNSS des ERP avec une résolution horaire avec le logiciel GINS/DYNAMO, développé et maintenu par le centre d’analyse français IGS GRG, géré par le CNES/CLS. Le choix de cette période assure une performance comparable entre les deux constellations. Nous avons testé les contraintes pour bloquer la bande rétrograde diurne (la nutation par convention).

Nous avons trouvé leur application bénéfique pour la détermination des autres bandes sub-diurnes, c’est-à-dire la bande diurne prograde et semi-diurnes prograde et rétrograde. Nous montrons également que pour une estimation horaire de UT1, il est nécessaire et suffisant de fixer les valeurs de UT1 à celles déterminées par les observations VLBI une fois par jour. Nous avons validé les solutions en comparant les réseaux terrestres et célestes résolus en même temps que les solutions ERP horaires aux réseaux des solutions finales GRG dans le cadre de la campagne IGS Repro3. Nous comparons les deux constellations par des analyses spectrales et harmoniques. Les séries temporelles des ERP après avoir retiré des effets de marées océaniques sont confrontées aux excitations géophysiques qui résultent de la circulation atmosphérique et océanique non-“maréale”, ainsi qu’à un développement harmonique dérivé des observations VLBI.

En parallèle, nous avons développé un nouveau modèle des effets sub-diurnes produits par les marées océaniques sur les ERP en nous fondant sur les derniers développements de la théorie du mouvement du pôle et de l’atlas des marées océaniques FES2014b. Une comparaison de ces résultats avec le développement harmonique VLBI met en évidence l’existence des termes de libration résultant de l’effet des marées luni-solaire sur la distribution asymétrique de la masse de la Terre dans le mouvement du pôle et l’UT1.

GNSS, mouvement du pôle, rotation de la Terre, marée océanique

Consulter la thèse (EN) : TEL-04792592

This thesis presents the first force measurements at close range between an atom and a surface, which was the ultimate objective of the Forca-G project.

The force is measured by atom interferometry with atoms trapped in potential wells formed by a vertical optical lattice. Stimulated Raman transitions are used to measure the energy difference between two wells, i.e. the force applied to the atoms. By moving the atoms to different distances from the mirror in a controlled manner using a Bloch lift, it is possible to measure variations in surface forces with a spatial resolution of the order of a micrometre. In the vicinity of the surface, a force measurement sensitivity of 3.4×10^-28 N has been achieved, which is state-of-the-art for surface force measurements. At atom-surface distances of less than a hundred micrometres, electrostatic forces dominate, due to the electrostatic fields generated by atoms adsorbed on the surface. By modelling these fields, another force is highlighted: the Casimir-Polder force. These parasitic electric fields have been measured directly with the trapped atoms, making it possible to correct, albeit imperfectly, the measurements of the impact of the electrostatic forces.

Finally, we have shown that the amplitude and the orientation of the atom-surface forces are modified by the illumination of the surface with UV light, which charges the surface.

quantum, interferometry, cold atoms, Casimir-Polder, trapped atoms

Full document (FR) : TEL-04680406

This PhD thesis work aims to propose innovative scientific and technological solutions for the demonstration a microcell-based CPT atomic clock with improved long-term frequency stability.

The first research axis has concerned the implementation of pulsed interrogation sequences used to reduce light shifts induced during the interaction pulses between the atoms and the optical interrogation field. The use of an advanced sequence named Symmetric Auto-Balanced Ramsey (SABR) has in particular allowed a reduction of the clock frequency sensitivity to variations of the optical field by more than two orders of magnitude, benefiting to the frequency stability for integration times higher than 100 s. A second research axis has led to the proof-of-concept and the development of a new alkali vapor microfabricated cell tehnology, based on hermetic laser-actuated break- and make-seals, combined with the use of low permeation glass substrates, for enhanced choice and reinforced control of the cell inner atmosphere. A reduction of the permeation rate by a factor higher than 1000 was demonstrated in cells filled with helium using aluminosilicate glass coupled with Al₂O₃ coatings. Studies for the development of cells using new buffer gas mixtures and working at high temperature (> 90 °C) have been undertaken. Complementary results of these two research axis led to the demonstration of a CPT atomic clock using a Cs-Ne microcell with aluminosilicate glass and operating with the SABR interrogation sequence.

The combination of these approaches, reinforced by additional active stabilization loops of some key experimental parameters, has led to a fractional frequency stability of 7×10⁻¹¹ at 1 s and 1.4×10⁻¹² at 10⁵ s. These stabilities at one day are competitive with those of the best microcellbased microwave clocks.

micro-atomic clocks, microfabricated cells, fractional frequency stability, buffer gas permeation, light-shifts, spectroscopie Ramsey

Full document (FR) : HAL-04474336

This thesis reports the development and characterization of an optical frequency reference at 895 nm based on the interrogation of cesium atoms confined in a microfabricated cell using dual-frequency sub-Doppler spectroscopy. This frequency reference includes a diode laser tuned on the cesium D1 line (895 nm), an electro-optic modulator, an acousto-optic modulator, a cesium vapor microcell and a control electronics.

Two nearly-identical laser systems were developed, one using a DFB diode laser and the other with an external cavity diode laser (ECDL). The beatnote between these two lasers demonstrated a frequency stability of 1.1×10^-12 at 1 s, limited by the intermodulation effect induced by the laser frequency noise.

An ultra-stable frequency reference at 895 nm was developed to unambiguously characterize the individual performance of the microcell ECDL. The latter is based on an annex ECDL, phase locked to a spectrally-broadened frequency comb, referenced to an ultra-stable Fabry-Perot cavitystabilized 1542 nm laser. A compensated fiber link, with a residual phase noise of –55 dB‧rad²/Hz at 1 Hz, was developed to transfer the signal of the reference.

Beating with the reference, the microcell ECDL laser has demonstrated a short-term frequency stability of 2.9×10^-13 at 1 s, in good agreement with its phase noise (+40 dB‧rad²/Hz at f = 1 Hz), and better than 5×10^-14 at 100 s. These performances are competitive with the best current microcell frequency references.

In a last step, preliminary studies were initiated to measure the sensitivity of laser frequency to variations of some experimental parameters. Among the evaluated effects, the misalignment between both counter-propagating beams, the microwave power, and the magnetic field appear to be important contributions to the laser mediumterm stability.

frequency reference, cesium microcell, sub-Doppler spectroscopy, frequency stability, laser

Full document (FR) : HAL-04412404

This PhD reports on the development of a transportable iodine frequency stabilized laser setup, based on compact and fibered Telecom components with a TRL. This laser system is an ultra-stable frequency reference for the assembly, integration, validation and tests (AIVT) of the payload of the LISA mission 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.

The solution delivered by the SYRTE to the CNES comprises two Nd:YAG lasers phase locked on each other, with the master itself being phase locked on a frequency reference. The frequency reference is a telecom fiber laser which frequency has beean tripled using non-linear optics and frequency locked to a hyperfine transition of an iodine vapour. The frequency residual noise of this setup is in the 10⁻¹⁴ range below 30 s in terms of Allan standard deviation. Its optical setup fits in 30 L and it has proven to be transportable.

ultrastable laser, non-linear optics, transportable laser, compact laser, fiber laser, frequency reference, LISA

Full document (FR) : HAL-04511838

This thesis consists of the implementation and study of new experimental techniques to improve the performance of the SYRTE’s dual-axis cold atom gyroscope experiment. The instrument represents the state of the art of matter wave gyroscopes and uses stimulated Raman transitions to perform a 4-pulse interferometer. This geometry results in a Sagnac area of 11 cm² for 800 ms interrogation time.

In this thesis, we detail a fundamental physics test with the cold-atom gyroscope which consists of a validity test of the Sagnac Effect with a matter-wave interferometer. The results from a year-long experimental campaign are presented, demonstrating a 20-fold improvement in accuracy over previous efforts in measuring the gyroscope scale factor, and corresponding to a 23 ppm accuracy level.

Additionally, this work also discusses two novel real-time methods to control the phase of the interferometer using Raman frequency jumps and mirror position jumps rather than using Raman laser’s relative phase jump. We provide a thorough description of both methods and delve into the particulars of their physical implementation, which is also characterized in detail. A comparative analysis of the performance of these two methods is also presented.

This work opens the path for the possibility of real time atomic phase compensation to any atom interferometer based on two photon transitions for the atomic wave diffraction and in particular when using Raman double diffraction regime for space applications.

atom interferometry, inertial sensor, cold atoms, test of fundamental physics

Full document (EN) : HAL-04346752

Atom sensors are highly sensitive devices used in time and frequency standards, as well as inertial sensing and precision measurements of electromagnetic fields. Nowadays, they are developed to the extent that they can be limited by their quantum nature, i.e., the standard quantum limit (SQL). This limit arises from the individual and uncorrelated behaviour of the used atoms. However, it has been demonstrated that one can overcome this limit via the generation of quantum correlations and entanglement between the atoms.

Proof of principle entanglement generation can be accomplished via different protocols, but this has very seldom been done in metrology-grade devices. In this thesis, we use a cavity quantum electrodynamics (cQED) platform to create a type of quantum correlated state named spin squeezed. We use as a platform a trapped-atom clock on a chip (TACC) to generate these entangled states.

This metrology-grade device allows us to study the dynamics due to spin interactions in the long time scale, on the order of a second. The stability of the apparatus is confirmed by a fractional frequency Allan deviation of 6×10⁻¹³ at 1 s, a performance beating commercially available compact atom clocks.

quantum metrology, atom chip, entranglement, atomic clock, spin-squeezed states, cavity quantum electrodynamics

Full document (EN) : HAL-04597522

At the micrometer scale, atom-surface interactions are dominated by the Casimir-Polder potential. This thesis is part of the development of the ForCa-G (Casimir Force and Short Range Gravitation) experiment where the measurement of short range forces (around the micrometer range) is performed using ⁸⁷Rb atoms cooled to temperatures of the order of a few hundred nano-kelvin and trapped in a vertical optical lattice in the vicinity of a dielectric surface.

In order to avoid contamination of this surface during the cooling steps, the atoms are prepared 30 cm below. We prove the efficiency of our transport method using Bloch oscillations, allowing both a satisfactory control of their final position without heating or excessive enlargement of the cloud radius in the vertical direction. An efficiency of up to 30% of the initial number of atoms has been measured after transport, which drops to 10% after recapture in the vertical lattice.

A sequence of stimulated Raman transitions then allows the spatial and coherent separation of the atomic wave packets on adjacent wells of the lattice and their recombination. This interferometer allows us to measure the energy difference between these wells, which is related to the different potentials seen by the atoms. A first measurement has been performed up to a distance of 1 µm from the surface, demonstrating the appearance of an attractive potential near the surface. However, initial analyses suggest that a parasitic electric field due to the adsorption of Rubidium atoms on the surface adds to the expected Casimir-Polder potential contribution.

cold atoms, atom interferometry, Casimir-Polder

Full document (FR) : HAL-04514581