Ultra-cold dilute gases of neutral atoms are attractive candidates for creating controlled mesoscopic quantum systems. In particular, quantum degenerate gases of bosonic and fermionic atoms can be used to model the correlated many-body behaviour of Bose and Fermi condensed matter systems, and to study matter wave interference and coherence. This thesis describes the experimental realization and manipulation of Bose-Einstein condensates (BECs) of 87Rb and degenerate Fermi gases (DFGs) of 40K using static and dynamic magnetic atom chip traps. Atom chips are versatile modern tools used to manipulate atomic gases. The chips consist of micrometre-scale conductors supported by a planar insulating substrate, and can be used to create confining potentials for neutral atoms tens or hundreds of micrometres from the chip surface. We demonstrate for the first time that a DFG can be produced via sympathetic cooling with a BEC using a simple single-vacuum-chamber apparatus. The large 40K-87Rb collision rate afforded by the strongly confining atom chip potential permits rapid cooling of 40K to quantum degeneracy via sympathetic cooling with 87Rb. By studying 40K-87Rb cross-thermalization as a function of temperature, we observe the Ramsauer-Townsend reduction in the 40K-87Rb elastic scattering cross-section. We achieve DFG temperatures as low as T = 0.1TF , and observe Fermi pressure in the time-of-flight expansion of the gas. This thesis also describes the radio-frequency (RF) manipulation of trapped atoms to create dressed state double-well potentials for BEC and DFG.We demonstrate for the first time that RF-dressed potentials are species-selective, permitting the formation of simultaneous 87Rb double-well and 40K single-well potentials using a 40K-87Rb mixture. We also develop tools to measure fluctuations of the relative atom number and relative phase of a dynamically split 87Rb BEC. In particular, we observe atom number fluctuations at the shot-noise level using time-of-flight absorption imaging. These measurement tools lay the foundation for future investigations of number squeezing and matter wave coherence in BEC and DFG systems.

Ultra-cold dilute gases of neutral atoms are attractive candidates for creating controlled mesoscopic quantum systems. In particular, quantum degenerate gases of bosonic and fermionic atoms can be used to model the correlated many-body behaviour of Bose and Fermi condensed matter systems, and to study matter wave interference and coherence. This thesis describes the experimental realization and manipulation of Bose-Einstein condensates (BECs) of 87Rb and degenerate Fermi gases (DFGs) of 40K using static and dynamic magnetic atom chip traps. Atom chips are versatile modern tools used to manipulate atomic gases. The chips consist of micrometre-scale conductors supported by a planar insulating substrate, and can be used to create confining potentials for neutral atoms tens or hundreds of micrometres from the chip surface. We demonstrate for the first time that a DFG can be produced via sympathetic cooling with a BEC using a simple single-vacuum-chamber apparatus. The large 40K-87Rb collision rate afforded by the strongly confining atom chip potential permits rapid cooling of 40K to quantum degeneracy via sympathetic cooling with 87Rb. By studying 40K-87Rb cross-thermalization as a function of temperature, we observe the Ramsauer-Townsend reduction in the 40K-87Rb elastic scattering cross-section. We achieve DFG temperatures as low as T = 0.1TF , and observe Fermi pressure in the time-of-flight expansion of the gas. This thesis also describes the radio-frequency (RF) manipulation of trapped atoms to create dressed state double-well potentials for BEC and DFG.We demonstrate for the first time that RF-dressed potentials are species-selective, permitting the formation of simultaneous 87Rb double-well and 40K single-well potentials using a 40K-87Rb mixture. We also develop tools to measure fluctuations of the relative atom number and relative phase of a dynamically split 87Rb BEC. In particular, we observe atom number fluctuations at the shot-noise level using time-of-flight absorption imaging. These measurement tools lay the foundation for future investigations of number squeezing and matter wave coherence in BEC and DFG systems.

La première partie décrit trois expériences réalisées avec l'interféromètre atomique à jet de lithium supersonique développé à Toulouse. La seconde partie présente le nouvel interféromètre atomique à condensats de Bose-Einstein (CBE) développé dans le but de tester la neutralité de la matière. Les trois premières expériences exploitent l'interaction entre un atome de lithium et différents champs électromagnétiques. Une différence de potentiel électrique dépendant du temps a servi à moduler la phase des deux bras de notre interféromètre à des fréquences différentes, ce qui a permis une détection homodyne et hétérodyne d'ondes de matière. Une phase géométrique de la lumière (la phase de Pancharatnam) a été transférée à notre signal interférométrique par les réseaux de diffraction de Bragg ce qui a ajouté un nouvel outil à la panoplie permettant le contrôle d'ondes de matières. Enfin, un faisceau laser focalisé sur un seul des deux bras nous a permis de mesurer avec exactitude une des longueurs d'onde d'extinction du lithium (correspondant à une valeur de polarisabilité dynamique nulle). L'objectif du nouvel interféromètre à CBE est de réaliser une nouvelle mesure de la charge électrique résiduelle de la matière et en particulier des isotopes du rubidium 85Rb et 87Rb. Cette mesure nous permettra de connaître avec une plus grande sensibilité la différence de charge entre le proton et l'électron ainsi que la charge du neutron. Le principe de cette mesure repose sur une séparation spatiale importante entre les deux bras d'un interféromètre en fontaine ainsi que sur un temps de cycle de 5 s. Ces caractéristiques ont nécessité un travail de conception à la fois au niveau de la source (une puce à atome) et au niveau du phénomène de diffraction (séparation en impulsion importante) qui sera exposé dans un premier temps. Dans un second temps, les choix techniques en matière de chambre à vide, système laser et sources de champs magnétiques seront décrits et caractérisés. Enfin, les performances actuelles de cette source d'atomes froids seront présentées et comparées à nos attentes. / This thesis's first part describes the realization of three experiments using an atom interferometer operated with a lithium supersonic beam. The second part presents the development of a new BEC interferometer designed to test matter neutrality. The first three experiments rely on the interactions of lithium atom with different electromagnetic fields. A time dependent electric potential difference was used to produce phase modulation of both interferometer arms at different frequencies, leading to homodyne and heterodyne detection of atom waves. A geometric phase of light (the Pancharatnam phase) was successfully transferred to our interferometer signal during Bragg diffraction, enlarging the atom optics toolbox for phase control in an atom interferometer. Finally, a focused laser beam was used to measure accurately the value of one lithium tune-out wavelength (for which its dynamic polarizability is zero). The new BEC interferometer was designed to measure a possible non-zero electric charge of rubidium isotopes 85Rb and 87Rb with enhanced sensitivity to the electron-proton charge difference and neutron neutrality. This setup relies on a large spatial separation between the two interferometer arms in a fountain configuration aiming at a cycle time of 5s. These features required particular design work both on the atomic source (atom-chip) and the diffraction process (Large Momentum Transfer). The technical choices on the vacuum chambers, laser system and magnetic sources are described and characterized. Finally, the up-to-date cold-atom source performances is shown and compared to our expectations.

<p dir="ltr">Quantum-enhanced approaches enable high-resolution imaging and sensing with signal-to-noise ratios beyond classical limits. However, operating in the quantum regime is highly susceptible to environmental influences and experimental conditions. Implementing these techniques necessitates highly controlled environments or intricate preparation methods, which can restrict their practical applications. This thesis explores the practical applications of quantum sensing, focusing on thermal sensing with bright quantum sources in biological and electronic contexts. Additionally, I discuss the development of a multimode source for quantum imaging applications and an on-chip atomic interface for scalable light-atom interactions. I built all the experimental setups from the beginning; a microscope setup for nanodiamond-based thermal sensing inside living cells, a four-wave mixing setup using a Rb cell for thermal imaging of microelectronics and multimode source, and a vacuum chamber for on-chip atomic interface.</p><p dir="ltr">Quantum sensing can be realized using atomic spins or optical photons possessing quantum information. Among these, color centers inside diamonds stand out as robust quantum spin defects (effective atomic spins), maintaining their quantum properties even in ambient conditions. In this thesis, I studied the role of an ensemble of color centers inside nanodiamonds as a probe of temperature in a living cell. Our approach involves incubating nanodiamonds in endothelial culture cells to achieve sub-kelvin sensitivity in temperature measurement. The results reveal a temperature error of 0.38 K and a sensitivity of 3.46 K/sqrt(Hz)<i> </i>after 83 seconds of measurement. Furthermore, I discuss the constraints of nanodiamond temperature sensing in living cells, propose strategies to surmount these limitations, and explore potential applications arising from such measurements.</p><p dir="ltr">Another ubiquitous quantum probe is light with quantum properties. Photons, the particles of light, can carry quantum correlations and have minimal interactions with each other and, to some extent, the environment. This capability theoretically allows for quantum-enhanced imaging or sensing of sample’s properties. In this thesis, I report on the demonstration of quantum-enhanced temperature sensing in microelectronics using bright quantum optical signals. I discuss the first demonstration of quantum thermal imaging used to identify hot spots and analyze heat transport in electronic systems.</p><p dir="ltr">To achieve this, we employed lock-in detection of thermoreflectivity, enabling us to measure temperature changes in a micro-wire induced by an electric current with an accuracy better than 0.04 degrees, averaged over 0.1 seconds. Our results demonstrate a nearly 50 % improvement in accuracy compared to using classical light at the same power, marking the first demonstration of below-shot-noise thermoreflectivity sensing. We applied this imaging technique to both aluminum and niobium-based circuits, achieving a thermal resolution of 42 mK during imaging. We scanned a 48 × 48 μm<i> </i>area with 3-4 dB squeezing compared to classical measurements. Based on these results, we infer possibility of generating a 256×256 pixel image with a temperature sensitivity of 42 mK within 10 minutes. This quantum thermoreflective imaging technique offers a more accurate method for detecting electronic hot spots and assessing heat distribution, and it may provide insights into the fundamental properties of electronic materials and superconductors.</p><p dir="ltr">In transitioning from single-mode to multimode quantum imaging, I conducted further research on techniques aimed at generating multimode quantum light. This involved an in-depth analysis of the correlation characteristics essential for utilizing quantum light sources in imaging applications. To achieve the desired multimode correlation regime, I developed a system centered on warm Rubidium vapor with nonlinear gain and feedback processes. The dynamics of optical nonlinearity in the presence of gain and feedback can lead to complexity, even chaos, in certain scenarios. Instabilities in temporal, spectral, spatial, or polarization aspects of optical fields may arise from chaotic responses within an optical <i>x</i>(2) or <i>x</i>(3) nonlinear medium positioned between two cavity mirrors or preceding a single feedback mirror. However, the complex mode dynamics, high-order correlations, and transitions to instability in such systems remain insufficiently understood.</p><p dir="ltr">In this study, we focused on a <i>x</i>(3) medium featuring an amplified four-wave mixing process, investigating noise and correlations among multiple optical modes. While individual modes displayed intensity fluctuations, we observed a reduction in relative intensity noise approaching the standard quantum limit, constrained by the camera speed. Remarkably, we recorded a relative noise reduction exceeding 20 dB and detected fourth-order intensity correlations among four spatial modes. Moreover, this process demonstrated the capability to generate over 100 distinct correlated quadruple modes.</p><p dir="ltr">In addition to conducting multimode analysis to develop a scalable imaging system, I have explored methodologies aimed at miniaturizing light-atom interactions on a chip for the scalable generation of quantum correlations. While warm atomic vapors have been utilized for generating or storing quantum correlations, they are plagued by challenges such as inhomogeneous broadening and low coherence time. Enhancing control over the velocity, location, and density of atomic gases could significantly improve light-atom interaction. Although laser cooling is a common technique for cooling and trapping atoms in a vacuum, its implementation in large-scale systems poses substantial challenges. As an alternative, I focused on developing an on-chip system integrated with atomic vapor controlled by surface acoustic waves (SAWs).</p><p dir="ltr">Surface acoustic waves are induced by an RF signal along the surface of a piezoelectric material and have already been proven to be effective for manipulating particles within microfluidic channels. Expanding upon this concept, I investigated the feasibility of employing a similar approach to manipulate atoms near the surface of a photonic circuit. The interaction between SAWs and warm atomic vapor is expected as a mechanism for controlling atomic gases in proximity to photonic chips for quantum applications. Through theoretical analysis spanning molecular dynamics and fluid dynamics regimes, I identified the experimental conditions necessary to observe acoustic wave behavior in atomic vapor. To validate this theory, I constructed an experiment comprising a vacuum chamber housing Rb atoms and a lithium niobate chip featuring interdigital transducers for launching SAWs. However, preliminary experimental results yielded no significant signals from SAW-atom interactions. Subsequent analysis revealed that observing such interactions requires sensitivity and signal-to-noise ratio (SNR) beyond the capabilities of the current setup. Multiple modifications, including increasing buffer gas pressure and mitigating RF cross-talk, are essential for conclusively observing and controlling these interactions.</p>

<p>Bose-Einstein condensates (BECs) in light-induced synthetic gauge fields and spaces can provide a highly-tunable platform for quantum simulations. Chapter 1 presents a short introduction to the concepts of BECs and our BEC machine. Chapter 2 introduces some basic ideas of how to use light-matter interactions to create synthetic gauge fields and spaces for neutral atoms. Three main research topics of the thesis are summarized below.</p> <p>Chapter 3: Recently, using bosonic quasiparticles (including their condensates) as spin carriers in spintronics has become promising for coherent spin transport over macroscopic distances. However, understanding the effects of spin-orbit (SO) coupling and many-body interactions on such a spin transport is barely explored. We study the effects of synthetic SO coupling (which can be turned on and off, not allowed in usual materials) and atomic interactions on the spin transport in an atomic BEC.</p> <p>Chapter 4: Interplay between matter and fields in physical spaces with nontrivial geometries can lead to phenomena unattainable in planar spaces. However, realizing such spaces is often impeded by experimental challenges. We synthesize real and curved synthetic dimensions into a Hall cylinder for a BEC, which develops symmetry-protected topological states absent in the planar counterpart. Our work opens the door to engineering synthetic gauge fields in spaces with a wide range of geometries and observing novel phenomena inherent to such spaces.</p> <p>Chapter 5: Rotational properties of a BEC are important to study its superfluidity. Recent studies have found that SO coupling can change a BEC's rotational and superfluid properties, but this topic is barely explored experimentally. We study rotational dynamics of a SO-coupled BEC in an effective rotating frame induced by a synthetic magnetic field. Our work may allow for studying how SO coupling modify a BEC's rotational and superfluid properties.</p> <p>Chapter 6 presents some possible future directions.</p>