Optical lattice clocks (OLCs) have achieved an unprecedented relative systematic uncertainty of about 10⁻¹⁹, establishing them as candidates for the upcoming redefinition of the second in the International System of Units (SI). Currently, the accuracy of OLCs is primarily limited by black body radiation (BBR), cold collisions, and lattice light shift effects. Various strategies are being explored to mitigate these limitations, including using cryogenic environments to manage BBR and using new trapping geometries to control atomic distributions and interactions.

In this project, we propose a new OLC setup that aims to characterize BBR and density effects below the 10⁻¹⁸ level. To achieve this goal, we have developed a copper science chamber that is placed inside a primary vacuum chamber. This configuration minimizes temperature inhomogeneities around the atoms to within a few tens of millikelvin (mK). The system features an adaptable one-dimensional (1D) optical lattice shaped with Laguerre-Gaussian LG_0ℓ modes to increase the number of trapping sites while reducing atomic occupancy per site. We created shaped lattices with values of ℓ from 0 to 4 whose trap depths were compatible with clock operation. We trapped thousands of Strontium atoms in TEM₀₀, LG₀₁ and LG₀₂ shaped lattices and performed low-resolution clock spectroscopy on bosonic ⁸⁸Sr, yielding 100 Hz-wide transitions.

To investigate cold collision effects, we plan to implement a second cooling stage using the ¹S₀ → ³P₁ intercombination transition in strontium. This will increase atomic density, enhancing observable collision effects and enabling the detection of motional sidebands. These measurements will provide insight into the anharmonicity of LG-shaped lattices and help validate the lattice light shift model under varying trap conditions. Finally, the clock setup is still under construction. Current work focuses on enclosing the interrogation chamber within the primary vacuum to improve the thermal homogeneity and reduce the uncertainty related to BBR, and at the same time, the instrumentation required for high-resolution spectroscopy is currently being installed.

atomic clock, optical lattice clock, optical lattice, light shift, systematic effects, blackbody radiation, cold collisions, Laguerre-Gaussian modes.

Full document (EN) : HAL-TEL-05556321

Atomic interferometry is a robust experimental method for carrying out high precision measurements, notably of the gravitational acceleration g and the fine structure constant α. Despite the remarkable performance already achieved, the accuracy of today’s best instruments is still limited by several systematic effects, chiefly wave front distortions and spatial inhomogeneities in laser beam intensity.

To quantify their impact, a Monte Carlo simulation was developed that faithfully reproduces two atom interferometry experiments: the LTE atomic gravimeter and the LKB measurement of the h/m ratio. This thesis is devoted to analysing and interpreting the results obtained with these two set ups, with the aim of identifying and modelling the main systematic biases that limit measurement accuracy. For each experiment, a complete numerical model was built for the interferometer sequence and the associated measurement protocols.

Gravimeter : The model allows to evaluate the systematic effect of the laser beam’s Gouy phase. Particular attention was paid to contrast losses caused by intensity inhomogeneity: the resulting phase spread leads to a marked reduction in fringe visibility. These predictions were compared with experimental data obtained by two independent probe pulse techniques that impose a light shift on the atomic energy levels. A model was developed to reproduce the non-monotonic contrast behaviour observed experimentally, taking account of parasitics interferences with the Raman beam. h/m measurement : The Monte Carlo code was adapted to a configuration that uses a Bose-Einstein condensate as a spatial probe for mapping the wave vector distribution and intensity profile of a Bloch beam. After assessing the contributions of the Gouy phase and the beams’ phase curvature, the distribution of measured atomic recoil was modelled when the Bloch beam is diffracted by a circular aperture, reproducing the extra recoil effect seen experimentally in low intensity regions where the recoil exceeds the nominal value hν/c.

atomic interferometry, quantum metrology, cold atoms, Monte Carlo simulation, wavefront aberrations, Raman transitions, Bloch oscillations.

Full document (FR) : TEL-05374402

This thesis context is the study of the ultimate performance of a microwave clock based on laser-cooled atoms. This clock, called MuClock, is fully integrated and automated within a volume of 0.7 m³. Its principle of operation is designed around its copper spherical cavity, which serves as both a microwave resonator and an integrating sphere to generate the isotropic cooling light field for the atoms. The MuClock measures the hyperfine transition frequency of the ⁵S_1/2 state of rubidium 87 using a sequence consisting of three distinct steps. First, by using 1,560 nm frequency doubling technologies, 10 million atoms are cooled to a temperature of about 70 µK through the isotropic cooling method. Next, the Ramsey spectroscopy method is used by applying two microwave pulses separated by an effective Ramsey time of 40 ms to interrogate the free falling atom cloud within the cavity. Finally, approximately 2 million atoms are detected through absorption of a vertical light beam. This sequence lasts about 150 ms and allows the MuClock to achieve a relative clock frequency stability performance of 3-5 ×10⁻¹³ at 1 second and 1×10⁻¹⁵ for over a month.

The goal of this thesis is to assess the clock frequency accuracy budget with a total uncertainty of less than 5×10⁻¹⁴. Each of the systematic effects contributing to the frequency shift of the MuClock is studied in this thesis. The largest of these, the quadratic Zeeman effect, is corrected by probing the magnetic transitions of the atoms. Another effect that cannot be measured by using the atoms is the phase transient effect, for which a specific measurement setup was designed. The measurements realized allow to optimize the clock sequence to reduce the contribution of this effect. This setup is also used to measure the dynamic end-to-end cavity phase shift during the interrogation of the atoms. This effect is eliminated by adjusting the MuClock's cavity heating method. Furthermore, a tomography imaging experiment is conducted to model the spatial distribution of the atoms. This model is validated by numerical simulations reconstructing the Rabi oscillation signals and Ramsey fringes of the MuClock. The spatial distribution of the atoms, as modelled, allows the estimation of several systematic effects such as the collisions between cold atoms or the distributed cavity phase shifts. This phase distribution is modeled from finite element simulations of the microwave resonance mode in the cavity. These simulations are also used to better understand the cavity pulling effect, whose contribution is made negligible by locking the cavity's resonance frequency. The Ramsey and Rabi pulling effects are measured using Ramsey spectroscopy with varying effective durations. The blackbody radiation effect is evaluated from measurements taken on atomic fountains. Finally, several effects, such as light shifts or off-resonance excitation phenomena are checked to ensure their contributions to the accuracy budget are negligible.

At the end of these studies, we estimate that the accuracy of a MuClock can be defined with an uncertainty of 1.4×10⁻¹⁴ at best. Frequency measurements of the MuClock against the frequency references of the Laboratoire Temps-Espace validate the evaluated clock frequency with a deviation of less than 1×10⁻¹⁴. The uncertainty for these measurements is 3×10⁻¹⁴, which is the current MuClock accuracy.

cold atoms, Rubidium, microwave clock, laser-cooling, accuracy budget.

Full document (FR) : not available because subject to an embargo until the 19^th May 2027.

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SPARMA F., ARCHAMBAULT L., Pelle B., LORINI L., LANDRAGIN A., DESRUELLE B. and Rosenbush P., “Accuracy assessment of a commercial cold-atom Rb clock: A use case within the Qu-Test project”, 37^th European Frequency and Time Forum (EFTF-2024), Neuchâtel, Switzerland, 25-27 June 2024, DOI: 10.1109/EFTF61992.2024.10722204.

ZYSKIND C., BIZE S., LODEWYCK J., POINTARD B., LE TARGAT R. et al., “First observation of the bosonic ¹⁹⁸Hg clock transition in an optical lattice clock”, 37^th European Frequency and Time Forum (EFTF-2024), Neuchâtel, Switzerland, 25-27 June 2024.

RIVERA AGUILAR C.M., CALLEJO M., MURSA A., CARLÉ C., VICARINI R., ABDEL HAFIZ M., FRIEDT J.-M., PASSILLY N. and BOUDOT R., “A Ramsey-CPT microcell atomic clock using laser current pulsed modulation”, International Network for Microfabricated Atomic Quantum Sensors (INMAQS 2024), Satellite Workshop of 37^th European Frequency and Time Forum (EFTF-2024), Neuchâtel, Switzerland, 28 June 2024.

LANDRAGIN A., GUESSOUM M. and GEIGER R., “High-performance gyroscope for rotational seismology”, Young Atom Opticians 2024, Strasbourg, France, 30 June - 5 July 2024, Pres.: HAL-04749791.

PAGOT L., PEREIRA DOS SANTOS F. and MERLET S., « Impact du front d’onde des faisceaux Raman sur la phase d’un interféromètre atomique », 10^e Congrès général de la Société Française d'Optique (OPTIQUE Normandie 2024), Rouen, France, 1-5 July 2024.

PEROUX L., MURSA A., DEWILDE A., TANGUY Q., CHUTANI RAVINDER K., CARLÉ C., VICARINI R., ABDEL HAFIZ M., BOUDOT R., MAURICE V. and PASSILLY N., « Cellules à vapeur alcaline microfabriquées à atmosphère contrôlée pour les capteurs atomiques », 10^e Congrès général de la Société Française d'Optique (OPTIQUE Normandie 2024), Rouen, France, 1-5 July 2024.

KNABE A., SCHILLING M., ROMESHKANI M., HOSSEINIARANI A., FLETLING N. et al., “Comprehensive in-orbit performance evaluation of quantum sensors for future satellite gravity missions and Space navigation”, Gravity, Geoid and height systems 2024 Symposium (GGHS 2024), Thessaloniki, Greece, 4-6 Sept. 2024, HAL-04760779.

LANDRAGIN A., GUESSOUM M., GEIGER R. and MARLIERE N., “High-performance gyroscope for rotational seismology”, Frontiers of Matterwave Optics 2024 (FOMO 2024), Chania, Crete, Greece, 9-14 Sept. 2024, Pres.: HAL-04749914.

DARMON S., SALDUCCI C., BIDEL Y., CADORET M., MAÏNOS A. et al., “Development of a cold atom absolute airborne gravimeter”, Frontiers of Matterwave Optics 2024 (FOMO 2024), Chania, Crete, Greece, 9-13 Sept. 2024.

MHAMMEDI N., PIEST B., BEAUFILS Q., CORGIER R. and PEREIRA DOS SANTOS F., “Progress in implementation of Delta-Kick squeezing in an atom interferometer”, Frontiers of Matterwave Optics 2024 (FOMO 2024), Chania, Crete, Greece, 9-13 Sept. 2024, HAL-04760800.

PEREIRA DOS SANTOS F., BALLAND Y. and ABSIL L., “Measurement of short range forces with quectonewton stability”, Frontiers of Matterwave Optics 2024 (FOMO 2024), Chania, Crete, Greece, 9-13 Sept. 2024, HAL-04760745.

CARLÉ C., CALLEJO M., MURSA A., ABDEL-HAFIZ M., TANGUY Q., VICARINI R., MILLO J., MAURICE V., KLINGER E., PASSILLY N. and BOUDOT R., “Microfabricated vapor cell atomic clocks at FEMTO-ST”, Hot atomic Vapor Workshop, Stuttgart, Germany, 30 Sept.-2 Oct. 2024, Guest lecture.

LORINI L., ABGRALL M., POINTARD B., LE TARGAT R., Gerginov V. et al., “Present status and future perspectives of atomic fountain frequency standards participating to ACES ground infrastructure”, ACES Workshop 2024, European Space Research and Technology Centre (ESA-ESTEC), Noordwijk, Netherlands, 23-25 Oct. 2024, HAL-04945718.

LANDRAGIN A., « Capteurs quantiques à atomes froids : mesure du champ de pesanteur à toutes les échelles », Meeting of QuBitAF Project / PEPR Quantique, Lyon, France, 28-29 Oct. 2024, HAL-04779650.

LANCHEROS-NARANJO D., PESCHE M., MERLET S. and PEREIRA DOS SANTOS F., “Doppler phases in conter-propagating geometry of atom interferometers”, 2^nd Colloquium GdR TeQ, Paris, France, 13-15 Nov. 2024, https://gdrteq2024.sciencesconf.org/.

PAGOT L., LANCHEROS-NARANJO D., PESCHE M., MERLET S., SIDORENKOV L. et al., “Impact of Raman beam wavefront on the accuracy of an atomic gravimeter”, 2nd Colloquium GdR TeQ, Paris, France, 13-15 Nov. 2024, https://gdrteq2024.sciencesconf.org/, HAL-04797657.

This thesis is part of the ANR MAXSAW project, which aims to develop new components operating in the RF domain, adapted to the new 5G frequencies. Surface acoustic wave (SAW) filters are widely used to distinguish the different frequencies of RF signals. Unfortunately, the frequency of conventional SAW filters is limited to 3.7 GHz. Epitaxial thin films of LiNbO₃ on sapphire host guided acoustic waves that meet the demand for higher frequencies and efficiency.

We first produced LiNbO₃ thin films on sapphire substrates. Thin films of good crystalline quality were obtained. We also studied their acoustic properties using simulations, and confirmed the frequencies achievable with these structures.

Then, we simulated, designed and characterized SAW resonators based on LiNbO₃ thin films deposited on sapphire, and compared them with the state of the art. Promising acoustic devices were obtained. Finally, an application to the MAXSAW project is presented.

electrical characterisation, physical properties, piezoelectricity, acoustic waves, lithium niobate

This Thesis is embargoed until 23/09/2026.

The development of wide-band RF filters operating at high frequency is urgently needed for the implementation of the 5th generation (5G) communication infrastructure. LiNbO3 is a promising material for integration into bulk acoustic wave (BAW) resonators/filters adapted to high-frequency applications owing to its high piezoelectric properties. However, integrating this material typically involves ion-slicing/polishing techniques of single crystals, which pose challenges for thickness homogeneity and thus industrial-scale production.

In this thesis, we investigated the integration of highly-coupled 32.8°Y-LiNbO3 thin films grown by DLI-CVD in BAW resonators. We initially focused on optimizing the growth of pure phase LiNbO3 with (01-12) textured growth on a LaNiO3 seed layer. We then assessed the ferroelectric, pyroelectric, and piezoelectric properties of the grown LN films, obtaining values of P_s = 52 μC/cm², pi = 60 μC/m². K and e_(31,f) = -2.81 C/m², which are comparable to those of LN single crystal.

Next, we optimized the fabrication process for integration into a basic HBAR structure to evaluate the performance of the grown films. The HBARs demonstrated a k_eff² up to 22.4 % at a resonance frequency of 5.6 GHz. For integrating the grown films into SMRs, we first optimized the growth and studied the thermal stability of the ZnO/Pt Bragg reflector. This reflector was then used to fabricate 32.8°Y-LN based SMRs. Electrical characterization of the fabricated SMRs showed resonances at frequencies in the range of 5.2-5.7 GHz, indicating great potential for high-frequency RF filtering applications.

BAW resonators, thin films, CVD, structural properties, piezoelectricity

Confidential thesis until 03/10/2034.

Lead-free piezoelectric materials are actively investigated for energy harvesting, sensor and high-frequency acoustic wave devices. In this manuscript, different architectures and microfabrication processes based on lead-free LiNbO₃ and KTa1-xNb_xO₃ crystals single crystals are investigated.

In a first part, energy harvester of LiNbO₃ on silicon substrate is fabricated by using wafer bonding and polishing. The transducers attained one of the highest power densities (965 µW/cm²/g²) compared to Pb and Pb-free vibrational harvesting devices. Then, the scalability of the LiNbO₃/Si to MEMS technology devices is investigated with LiNbO₃ and silicon etching. The etching of LiNbO₃ have been performed by implementing a pulsed mode reactive ion etching by using Ar/SF₆ gas. Accelerometric sensor has been demonstrated.

In a second part, our interest moved toward flexible metallic substrates. A big step has been achieved by developing Au-Au bonding of LiNbO₃ to metal substrates. The performances of bimorph beam of LiNbO₃-stainless steel-LiNbO₃ attained 209.7 µW/cm²/g² at 39.3 Hz.

Finally, we investigate alternative lead-free piezoelectric materials of KTa1-xNb_xO₃ crystals, for SAW devices application. First, structural and microstructural characterization of the crystal was carried out followed by fabrication and characterization of one-port SAW resonator. An electrotechnical coupling of 80 % was achieved while 49 % was obtained for KNbO₃ resonators.

alkaline niobates and tantalates, piezoelectric energy harvesting, saw resonators, microfabrication

Confidential thesis until 15/07/2034.

This thesis explores the development of a transportable, ultra-narrow linewidth laser integrating a high-finesse Fabry-Perot cavity made from ultra-low expansion glass with optically contacted Fused Silica mirrors, aiming to minimize thermal and mechanical perturbations and enhance frequency stability. A novel digital frequency stabilization method using an FPGA-based platform is introduced, targeting a fractional frequency stability of 1×10^-15 at 1 s integration. This approach contrasts traditional analog systems by offering increased stability and reduced complexity. The study also examines several limitations of ultra-stable lasers like phase noise, thermal noise, etc. and several approaches to mitigate these types of noise. Additionally, an optical frequency dissemination system using FPGA-based phase-locked loops and optical fiber links is detailed, ensuring stable signal transmission over laboratory distances.

optical frequency standard, time and frequency metrology, ultra-stable oscillator, optical phase noise measurement, laser frequency stabilization

Full document (EN) : TEL-04823081

 Optical clocks have now reached accuracies close to 1×10⁻¹⁸. They are used for various applications, such as chronometric geodesy, tests of General Relativity, the search for physics beyond the Standard Model, and the redefinition of the SI second. 

Among neutral species, mercury has several attractive properties for an optical lattice clock, including a low sensitivity to blackbody radiation and a high vapor pressure at room temperature. Until now, the ¹⁹⁹Hg fermionic isotope was the only isotope used in mercury clocks. However, its limited lifetime in the excited state restricts the full potential of the upcoming generation of ultrastable lasers. Using bosonic isotopes instead offers a way to overcome this limitation, thanks to their potentially unlimited lifetime.

This thesis reports the first observation of the ¹⁹⁸Hg bosonic transition in an optical lattice clock, which was achieved through several key experimental advancements and a challenging search for a narrow transition across a wide uncertainty range. The bosonic clock transition is forbidden but it can become weakly allowed via a high magnetic field, a technique known as the quenching method. This approach enables longer probing times that can be adjusted to the laser properties. Therefore, the first critical step was developing a setup capable of generating a sufficiently large magnetic field to induce the bosonic transition with the highest possible coupling. Another challenge involved implementing a widely tunable and flexible probe laser while preserving its ultra-low noise characteristics, allowing the probing of any mercury isotope without introducing  additional noise. Since the coupling also increases with probe power, a major milestone was significantly boosting the power of our deep UV ultrastable light source.

Despite these experimental improvements, our calculations indicated that the coupling remained relatively weak, leading to a narrow-line transition that needed to be found over a broad frequency range. We conducted various measurements and checks, to optimize our chances of finding the transition. Thanks to these cumulative efforts, the search for the ¹⁹⁸Hg transition was successful, marking the first observation of a bosonic mercury isotope transition.

Building on this achievement, we established an operational optical lattice clock with the bosonic ¹⁹⁸Hg, already achieving a stability of 10⁻¹⁵ at 1 s. We have undertaken several studies of this new transition, including measuring the quadratic Zeeman shift coefficient with sufficient precision to control this shift to 10⁻¹⁷ or better. We have also begun investigating other systematic effects, such as the light shift, cold collisional shift, and lattice light shift, along with measuring the ¹⁹⁸Hg magic wavelength. We made a first series of comparing to ⁸⁷Sr and obtained a stability of 1.2×10⁻¹⁵ at 1 s for this comparison, paving the way for a first measurement of the ¹⁹⁸Hg/⁸⁷Sr optical frequency ratio. The work on the bosonic isotope will shortly lead to the possibility to implement more sophisticated probing methods (Hyper-Ramsey spectroscopy) that will improve the uncertainty to the limit of our current experimental setup.

This thesis also presents analyses and results obtained with the ¹⁹⁹Hg fermionic isotope during a fiber link clock comparison with several European institutes conducted in March/April 2023. 

optical lattice clock, mercury, fermionic and bosonic isotope

Full document (EN) : TEL-05034816

This thesis present the latest work realized on the absolute colds atoms gravimeter of the LNE-SYRTE. To measure g, this device, called CAG, realize an atomic interferometer with Raman pulses on a free falling atomic cloud of Rubidium 87. The accuracy of the CAG’s measurements are limited by the Raman beam, its phase and intensity profile. During the thesis, the apparatus was moved to the Observatoire de Paris to be upgraded, in order to reduce these effects and extending the limits of the CAG further.

After the restart of the device, which able us to reach similar sensibilities than previously at 20×10⁻⁹·g Hz^−1/2, the studies related to the Raman beam have been continued. The manuscript details this work, which guides to study the stability of the intensity of each Raman beam, as well as the impact of inhomogeneity in the intensity profile. This inhomogeneity has been proven to cause a light shift distribution within the atomic cloud, resulting in a loss of contrast. This phenomenon also cause a bias on the measurement of g, of the order of 5×10⁻⁹·g, which is not eliminated by the measurement algorithm, and should be taken into account into the uncertainty budget. We also present the first results of the optimal control of the Raman transitions. This experimental method aims to improve the efficiency of the transitions and, consequently, the contrast of the interferometer.

atomic interferometry, gravimeter, inertial sensor, colds atoms

Full document (FR) : TEL-05035515