D. J. Papoular

We theoretically identify observable consequences of spatial and spin symmetries on the dynamics of a small XXZ quantum simulator. Our proposed protocol relies on the choice of suitable initial states, and involves the measurement scheme whose experimental implementation is the simplest. We analyze a system of N = 2 n = 6 to 12 particles, trapped in a planar geometry comprised of two rings which exhibits point group symmetry D n h . The particles represent effective spins whose interaction is described by the XXZ or Heisenberg Hamiltonian. The system is prepared in an initial state which is sitewise-factorized and invariant under all spatial symmetries, it evolves for a given time, after which the z -components of all N spins are measured. We show that symmetries dictate ( i ) the qualitative behavior of the measurement probabilities as a function of the evolution time, and ( ii ) the number of measurement results with different probabilities. We highlight the role of a twofold rotation of all spins. We also demonstrate that, in larger systems, the collapse of the initial state may be observed.

Manipulation des interactions dans les gaz quantiques : approche théorique: Les interactions entre particules dans les gaz quantiques ultrafroids peuvent être contrôlées à l'aide de résonances de Fano-Feshbach. Ces résonances de diffusion se produisent lors de collisions à basse énergie entre deux atomes et sont généralement obtenues à l'aide d'un champ magnétique statique externe. Elles font des gaz atomiques ultrafroids un terrain d'exploration pour la recherche de nouvelles phases dans lesquelles la physique quantique joue un rôle clef.Le travail présenté dans ce mémoire s'inscrit dans le cadre de la recherche de telles phases.Ce manuscrit comporte deux parties. La première est consacrée à l'étude de bosons composites obtenus dans des gaz de Fermi hétéronucléaires 2D. Nous étudions le diagramme de phase de ce système à T = 0 et nous mettons en évidence une transition de phase gaz-cristal. Nos résultats sont prometteurs en vue d'expériences futures avec le mélange 6Li-40K.Dans la seconde partie, nous proposons un nouveau type de résonance de Fano-Feshbach. Le couplage à l'origine de cette résonance est obtenu à l'aide d'un champ magnétique micro-onde.Notre méthode s'applique à n'importe quelle espèce atomique dont l'état fondamental est clivé par l'interaction hyperfine. Elle ne nécessite pas l'utilisation d'un champ magnétique statique.Nous décrivons d'abord ces résonances à l'aide d'un modèle simple à deux niveaux. Ensuite, nous les caractérisons numériquement à l'aide de notre propre programme implémentant l'approche multi-canaux des collisions atomiques. Nos résultats ouvrent des perspectives optimistes en vue de l'observation des résonances de Feshbach induites par un champ micro-onde avec les atomes alcalins bosoniques suivants : 23Na, 41K, 87Rb et 133Cs.

Circular Rydberg atoms (CRAs), i.e., Rydberg atoms with maximal orbital momentum, ideally combine long coherence times and strong interactions, a key property of quantum systems, in particular for the development of quantum technologies. However, the dipole-dipole interaction between CRAs has not been observed so far. We report the measurement and characterization of the resonant dipole-dipole interaction between two CRAs, individually trapped in optical tweezers, and find excellent agreement with theoretical predictions. We demonstrate a dynamic control over the strength of the interaction by tuning the orientation of an electric field. We use the interaction between the CRAs as a meter for the interatomic distance, and record the relative motion between two atoms in their traps. This motion, that we induce through the interaction between Rydberg levels with permanent electric dipoles, transiently populated during the preparation of the circular states, is a signature of spin-motion coupling.

We study theoretically two consequences of the mixed classical phase space for three repulsively interacting bosonic particles in a circular trap. First, we show that the energy levels of the corresponding quantum system are well described by a Berry-Robnik distribution. Second, we identify stationary quantum states whose density is enhanced along the stable classical periodic trajectories, and calculate their energies and wave functions using the semiclassical Einstein-Brillouin-Keller (EBK) theory. Our EBK results are in excellent agreement with our full-fledged finite-element numerics. We discuss the impact of discrete symmetries, including bosonic exchange symmetry, on these classically localized states. They are within experimental reach, and occur in the same range of energies as the quantum scar reported in our previous work [ Phys. Rev. A 107, 022217 (2023)].

We study theoretically two consequences of the mixed classical phase space for three repulsively-interacting bosonic particles in a circular trap. First, we show that the energy levels of the corresponding quantum system are well described by a Berry-Robnik distribution. Second, we identify stationary quantum states whose density is enhanced along the stable classical periodic trajectories, and calculate their energies and wavefunctions using the semiclassical Einstein-Brillouin-Keller (EBK) theory. Our EBK results are in excellent agreement with our full-fledged finite-element numerics. We discuss the impact of discrete symmetries, including bosonic exchange symmetry, on these classically localized states. They are within experimental reach, and occur in the same range of energies as the quantum scar reported in our previous work [Phys. Rev. A 107, 022217 (2023)].

We propose theoretically a quantum scar affecting the motion of three interacting particles in a circular trap. We numerically calculate the quantum eigenstates of the system and show that some of them are scarred by a classically unstable periodic trajectory, in the vicinity of which the classical analog exhibits chaos. The few-body scar we consider is stabilized by quantum mechanics, and we analyze it along the lines of the original quantum scarring mechanism [ Phys. Rev. Lett. 53, 1515 (1984)]. In particular, we identify towers of scarred quantum states which we fully explain in terms of the unstable classical trajectory underlying the scar. Our proposal is within experimental reach owing to very recent advances in Rydberg atom trapping.

We theoretically propose a quantum scar affecting the motion of three interacting particles in a circular trap. We numerically calculate the quantum eigenstates of the system and show that some of them are scarred by a classically unstable periodic trajectory, in the vicinity of which the classical analog exhibits chaos. The few-body scar we consider is stabilized by quantum mechanics, and we analyze it along the lines of the original quantum scarring mechanism [Heller, Phys. Rev. Lett. 53, 1515 (1984)]. In particular, we identify towers of scarred quantum states which we fully explain in terms of the unstable classical trajectory underlying the scar. Our proposal is within experimental reach owing to very recent advances in Rydberg atom trapping.

Electrons on the liquid helium surface form an extremely clean two-dimensional system where different plasmon excitations can coexist. Under a magnetic field, time-reversal symmetry is broken, and all the bulk magnetoplasmons become gapped at frequencies below cyclotron resonance while chiral one-dimensional edge magnetoplasmons appear at the system perimeter. We theoretically show that the presence of a homogeneous density gradient in the electron gas leads to the formation of a delocalized magnetoplasmon mode in the same frequency range as the lowest-frequency edge-magnetoplasmon mode. We experimentally confirm its existence by measuring the corresponding resonance peak in frequency dependence of the admittance of the electron gas. This allows us to realize a prototype system to investigate the coupling between a chiral one-dimensional mode and a single delocalized bulk mode. Such a model system can be important for the understanding of transport properties of topological materials where states of different dimensionality can coexist.

We analyze theoretically the quantization of conductance occurring with cold bosonic atoms trapped in two reservoirs connected by a constriction with an attractive gate potential. We focus on temperatures slightly above the condensation threshold in the reservoirs. We show that a conductance step occurs, coinciding with the appearance of a condensate in the constriction. Conductance relies on a collective process involving the quantum condensation of an atom into an elementary excitation and the subsequent quantum evaporation of an atom, in contrast with ballistic fermion transport. The value of the bosonic conductance plateau is strongly enhanced compared to fermions and explicitly depends on temperature. We highlight the role of the repulsive interactions between the bosons in preventing them from collapsing into the constriction. We also point out the differences between the bosonic and fermionic thermoelectric effects in the quantized conductance regime.