Showing papers by "Sylvain Nascimbene published in 2022"

The cross-over from Townes solitons to droplets in a 2D Bose mixture

Abstract: When two Bose–Einstein condensates—labelled 1 and 2—overlap spatially, the equilibrium state of the system depends on the miscibility criterion for the two fluids. Here, we theoretically focus on the non-miscible regime in two spatial dimensions and explore the properties of the localized wave packet formed by the minority component 2 when immersed in an infinite bath formed by component 1. We address the zero-temperature regime and describe the two-fluid system by coupled classical field equations. We show that such a wave packet exists only for an atom number N 2 above a threshold value corresponding to the Townes soliton state. We identify the regimes where this localized state can be described by an effective single-field equation up to the droplet case, where component 2 behaves like an incompressible fluid. We study the near-equilibrium dynamics of the coupled fluids, which reveals specific parameter ranges for the existence of localized excitation modes.

Realization of an atomic quantum Hall system in four dimensions

Abstract: Topological states of matter lie at the heart of our modern understanding of condensed matter systems. In two-dimensional (2D) quantum Hall insulators, the non-trivial topology, defined by the first Chern number, manifests as a quantized Hall conductance [1, 2] and protected ballistic edge modes [3]. Besides topological insulators [4] and Weyl semi-metals [5, 6] experimentally realized in 3D materials, a large variety of topological systems, theoretically predicted in dimensions D > 3, remains unexplored [7] – among them a generalization of the quantum Hall effect in 4D [8, 9]. So far, topological properties linked with the 4D Hall effect have been revealed via geometrical charge pump experiments in 2D systems [10, 11]. A truly 4D Hall system has also been realized using electronic circuits – however, no direct evidence of topological quantization has been reported [12]. Here, we engineer an atomic quantum Hall system evolving in 4D, by coupling with light fields two spatial dimensions and two synthetic ones encoded in the electronic spin J = 8 of dysprosium atoms [13–15]. We measure the characteristic properties of a 4D quantum Hall system, namely the quantization of its electromagnetic non-linear response by a second Chern number, and the special nature of its 3D hyperedge modes, which combine ballistic motion along one orientation and insulating behaviour in the two remaining directions. We also probe lowlying excitations, revealing non-planar cyclotron orbits in contrast with their circular equivalents in D ≤ 3. Our findings pave the way to the exploration of interacting quantum Hall systems in 4D, from the investigation of strongly-correlated liquids [9, 16] to the simulation of high-energy models in link with quantum gravity [9] and YangMills field theory [17, 18]. Dimensionality plays a prominent role in the classification of topological physical systems [7]. While different topological classes have been explored in condensed matter systems [19] – effectively described in one, two or three dimensions – higher dimensional systems can potentially be accessed with engineered materials, based on the concept of synthetic dimensions [13, 20]. In particular, different protocols have been proposed to realize a

Precision measurement of atom-dimer interaction in a uniform planar Bose gas

Abstract: Cold quantum gases, when acted upon by electromagnetic fields, can give rise to samples where isolated atoms coexist with dimers or trimers, which raises the question of the interactions between these various constituents. Here we perform microwave photoassociation in a degenerate gas of $^{87}$Rb atoms to create weakly-bound dimers in their electronic ground state. From the density-induced shift of the photoassociation line, we measure the atom-dimer scattering length for the two least-bound states of the molecular potential. We also determine the complete energy diagram of one hyperfine manifold of the least-bound state, which we accurately reproduce with a simple model.