Probing superfluidity in a quasi two-dimensional Bose gas through its local dynamics

Abstract

We report direct evidence of superfluidity in a quasi two-dimensional Bose gas by observing its dynamical response to a collective excitation, the scissors mode. Relying on a novel local average analysis, we are able to probe inhomogeneous clouds and reveal their local dynamics. We identify in this way the superfluid and thermal phases inside the gas and locate the boundary at which the Berezinskii-Kosterlitz-Thouless crossover occurs. This new analysis also allows to evidence the coupling of the two fluids which induces at finite temperatures damping rates larger than the usual Landau damping.

Superfluid vortex dynamics on a spherical film

“…Proposed new experiments in microgravity conditions [14] means that our model of a thin "bubble" trapped BEC may be studied experimentally in the near future. In addition, recent experiments have studied a "bubble" trap potential in the presence of gravity [15,16], and it may soon be feasible to manipulate the trap rotation and the atomic parameters to fix various initial conditions. We anticipate that our theoretical studies will be relevant for any further studies on the evolution of vortex pairs on a sphere.…”

Strongly-Interacting Bosons in a Two-Dimensional Quasicrystal Lattice

“…This regime, known as the quasi-2D regime is the most usual one in ultracold-atom experiments, see for instance Refs. [48,73,81,82]. Since a 3D l ⊥ , the quasi-2D Bose gas is always in the weakly interacting regime, g 1.…”

“…Note that here we have defined the terms quasi-2D and purely-2D according to the respective values of the 3D scattering length a 3D and the oscillation length l ⊥ , similarly as in Refs. [51,63,70,77,82,84,85] for instance. Other authors define it by comparing the temperature k B T with the energy scale ω ⊥ , see for instance Refs.…”

Ultracold atoms in multiple radio-frequency dressed adiabatic potentials

“…A single RF applied on an atom chip [11] has been used to coherently split a 1D quantum gas [12], a technique since used to shed light on the nature of thermalisation in near-integrable 1D quantum systems [13]. RF 'dressed' adiabatic potentials (APs) have also been employed to probe 2D gases [14,15]. Ring traps can be implemented by time averaging [16,17] or by adding an optical dipole potential [18], and are used to study superflow or for matter-wave Sagnac interferometry [2].…”