In this thesis, I present the study of the laser trapping and cooling of a Dysprosium atomic gas. This latter belong to the lanthanide family, it exhibits a large angular momentum in its electronic ground state, making it a suitable candidate for investigating dipolar quantum gases. These systems present a major interest as they can lead to the observation of novel quantum phenomena thanks to the anisotropic and long-range character of the interaction between magnetic dipoles. Moreover, Dysprosium has a rich electronic structure offering the possibility to implement strong light-spin coupling with a reduced heating with respect to alkali species, which paves the way toward the realization of synthetic gauge fields.In this work, I present the experimental investigation of different interaction mechanisms occurring in an ultracold gas of Dysprosium, ranging from light-assisted collisions to dipolar relaxation and evaporative cooling. I expose also the experimental realization of an effective magnetic field, using spin-dependent light-shift, allowing optical control over atomic interactions by means of Feshbach resonances.
In this thesis, I present the study of the laser trapping and cooling of a Dysprosium atomic gas. This latter belong to the lanthanide family, it exhibits a large angular momentum in its electronic ground state, making it a suitable candidate for investigating dipolar quantum gases. These systems present a major interest as they can lead to the observation of novel quantum phenomena thanks to the anisotropic and long-range character of the interaction between magnetic dipoles. Moreover, Dysprosium has a rich electronic structure offering the possibility to implement strong light-spin coupling with a reduced heating with respect to alkali species, which paves the way toward the realization of synthetic gauge fields.In this work, I present the experimental investigation of different interaction mechanisms occurring in an ultracold gas of Dysprosium, ranging from light-assisted collisions to dipolar relaxation and evaporative cooling. I expose also the experimental realization of an effective magnetic field, using spin-dependent light-shift, allowing optical control over atomic interactions by means of Feshbach resonances.
Gaz de dysprosium ultrafroid dans des pièges dipolaires optiques : contrôle des interactions entre atomes fortement magnétiques Dans le cadre de cette thèse, j’ai étudié le refroidissement et le piégeage d’un gaz d’atomes de dysprosium dans des potentiels lumineux. Cet atome lanthanide possède dans son état électronique fondamental un moment magnétique très élevé, permettant l’exploration du domaine des gaz dipolaires ultrafroids. Ce caractère dipolaire enrichit la gamme des phénomènes physiques réalisés expérimentalement, en tirant avantage de la nature anisotrope et à longue-portée de l’interaction entre dipôles magnétiques. De plus, grâce à sa structure électronique riche, le Dysprosium offre la possibilité de créer un fort couplage entre le spin atomique et des champs lumineux, tout en gardant un taux de chauffage faible par rapport au cas usuel des atomes alcalins. Ceci ouvre la voie vers l’implémentation de champs de jauge artificiels, qui suscitent un vif intérêt dans le domaine des atomes froids dans un contexte de simulation quantique. Ce travail de thèse consiste en l’étude des mécanismes d’interactions dans un gaz de Dysprosium ultrafroid, allant des collisions assistées par la lumière à la relaxation dipolaire en passant par le refroidissement par évaporation. J’expose également la réalisation expérimentale d’un champ magnétique effectif en utilisant un déplacement lumineux dépendant du spin, permettant de contrôler optiquement la force des interactions atomiques au moyen d’une résonance de Feshbach.
This thesis manuscript presents experiments realized with ultracold atomic gases of dysprosium. This element has specific properties such as a large spin J=8 and tunable light-spin couplings originating from significant tensor light-shift contributions close to resonance. An overview of the experimental setup is given, from magneto-optical trapping to evaporative cooling. In particular we present the role of the tensor light-shift in the in-trap Doppler cooling process. Details on the use of spatial modulation to tune the shape of an optical dipole trap are also given. In the second part we describe the preparation of squeezed and ‘oversqueezed’ spin states as well as Schrödinger cat states using light-induced spin couplings. The magnetic sensitivity of these states is characterized using Ramsey spectroscopy. The Husimi function is reconstructed from population measurements along various directions, also allowing us to compute the purity of the prepared states. While squeezed states show an increased metrological gain, oversqueezed states exhibit a strong Ramsey oscillations contrast reduction. The Hellinger distance is used to extend the notion of metrological gain and the sensitivity measured in this case saturates the Cramér-Rao bound. Finally a system of 16 indistinguishable interacting spins 1/2 is realized. In the third part we present the measurement of pairwise entanglement from photon absorption measurements, which was not realized experimentally. Finally we present two projects where spatial degrees of freedom are added to the dynamics of internal levels. The first one consists in the realization of a system analogous to the Landau Hamiltonian of a charged particle in a magnetic field, with one spatial dimension and one synthetic dimension. The second project uses two spatial dimensions and exhibits an artificial magnetic field originating from positiondependent light-shifts.
This paper reviews current experimental and theoretical progress in the study of dipolar quantum gases of ground and meta-stable atoms with a large magnetic moment. We emphasize the anisotropic nature of Feshbach resonances due to coupling to fast-rotating resonant molecular states in ultracold s-wave collisions between magnetic atoms in external magnetic fields. The dramatic differences in the distribution of resonances of magnetic (7)S3 chromium and magnetic lanthanide atoms with a submerged 4f shell and non-zero electron angular momentum is analyzed. We focus on dysprosium and erbium as important experimental advances have been recently made to cool and create quantum-degenerate gases for these atoms. Finally, we describe progress in locating resonances in collisions of meta-stable magnetic atoms in electronic P-states with ground-state atoms, where an interplay between collisional anisotropies and spin-orbit coupling exists.
Since the achievement of quantum degeneracy in gases of chromium atoms in 2004, the experimental investigation of ultracold gases made of highly magnetic atoms has blossomed. The field has yielded the observation of many unprecedented phenomena, in particular those in which long-range and anisotropic dipole-dipole interactions (DDIs) play a crucial role. In this review, we aim to present the aspects of the magnetic quantum-gas platform that make it unique for exploring ultracold and quantum physics as well as to give a thorough overview of experimental achievements. Highly magnetic atoms distinguish themselves by the fact that their electronic ground-state configuration possesses a large electronic total angular momentum. This results in a large magnetic moment and a rich electronic transition spectrum. Such transitions are useful for cooling, trapping, and manipulating these atoms. The complex atomic structure and large dipolar moments of these atoms also lead to a dense spectrum of resonances in their two-body scattering behaviour. These resonances can be used to control the interatomic interactions and, in particular, the relative importance of contact over dipolar interactions. These features provide exquisite control knobs for exploring the few- and many-body physics of dipolar quantum gases. The study of dipolar effects in magnetic quantum gases has covered various few-body phenomena that are based on elastic and inelastic anisotropic scattering. Various many-body effects have also been demonstrated. These affect both the shape, stability, dynamics, and excitations of fully polarised repulsive Bose or Fermi gases. Beyond the mean-field instability, strong dipolar interactions competing with slightly weaker contact interactions between magnetic bosons yield new quantum-stabilised states, among which are self-bound droplets, droplet assemblies, and supersolids. Dipolar interactions also deeply affect the physics of atomic gases with an internal degree of freedom as these interactions intrinsically couple spin and atomic motion. Finally, long-range dipolar interactions can stabilise strongly correlated excited states of 1D gases and also impact the physics of lattice-confined systems, both at the spin-polarised level (Hubbard models with off-site interactions) and at the spinful level (XYZ models). In the present manuscript, we aim to provide an extensive overview of the various related experimental achievements up to the present.
Conception et construction d’une expérience de dysprosium ultrafroid : un nouveau cadre pour l’interaction lumière-spin Dans ce travail de thèse, je présente la construction d’une nouvelle expérience pour la production de gaz ultra froids de dysprosium. En tirant parti de la structure électronique à couche incomplète de ces atomes, nous visons à la réalisation de champs de jauge synthétiques, qui pourront conduire à l’observation de nouvelles phases (topologiques) de la matière. Le couplage du spin atomique avec le champ lumineux, plus efficace que pour des atomes alcalins, permettra d’atteindre des régimes d’interactions fortes qui restent, jusqu’à présent, hors de portée expérimentale. J’adapte des protocoles existants pour la réalisation de champs de jauge dans le cas de Dysprosium, en tenant compte de son grand spin électronique (J = 8 dans l’état fondamental). En outre, le dysprosium a le plus grand moment magnétique parmi les éléments stables, et il est donc le meilleur candidat pour l’étude des gaz dipolaires. Je détaille le dispositif expérimental que nous avons construit et comment nous effectuons le piégeage et le refroidissement du dysprosium. Nous étudions en détail le comportement du piège magnéto-optique, qui est réalisé sur la transition d’intercombinaison ¹S₀ ↔ ³P₁. La raie étroite et le grand spin rendent l’opération du piège très complexe. Néanmoins, je montre que sa compréhension devient assez simple dans le régime où le nuage se polarise spontanément en conséquence de la combinaison des forces optiques et gravitationnelles. Enfin, je décris les dernières étapes du transport optique et de l’évaporation, ce qui conduira à la production d’un gaz dégénéré.
This thesis presents novel techniques for the experimental study of ultracold quantum gases of fermionic lithium and potassium atoms.In the first part of this thesis, we describe the design and characterization of the new components of our experimental apparatus capable of trapping and cooling simultaneously 6Li and 40K atoms to ultracold temperatures.We report on a novel sub-Doppler cooling mechanism, operating on the D1 line transition of alkali atoms, for laser cooling of lithium and potassium. The measured phase space densities after this molasses phase are on the order of 10−4 for both 6Li and 40K. We present the forced evaporative cooling of 40K atoms, starting in an optically plugged magnetic quadrupole trap and continuing in an optical dipole trap. In this context, we report on the production of a quantum degenerate Fermi gas of 1.5×105 atoms 40K in a crossed dipole trap with T/TF=0.17, paving the way for the study of strongly interacting superfluids of 40K.In the second part of this thesis, we present a narrow-linewidth, all-solid-state laser source, emitting 5.2 W in the vicinity of the lithium D-line transitions at 671 nm. The source is based on a diode-end-pumped unidirectional ring laser operating on the 1342 nm transition of Nd:YVO4, capable of producing 6.5 W of single-mode light delivered in a diffraction-limited beam. We report on three different approaches for second-haromonic generation of its output beam, namely by employing an enhancement cavity containing a ppKTP crystal, intracavity frequency doubling and a ppZnO:LN waveguide structure.