Formation of vortex solitons and bright soliton necklaces in attractive two-dimensional Bose gases

Atomic quantum gases loaded in a box potential present a versatile platform for studying non-equilibrium dynamics unseen in conventional harmonic traps. In this talk, we present observation of an elusive ‘vortex soliton’ in a quenched attractive Bose gas. In our experiment, we create a quantum vortex in a homogeneous two-dimensional (2D) superfluid confined in an optical box and quench the atomic interaction to an attractive value during a 2D time-of-flight. By adjusting the attractive interaction, we observe that a 2D gas can evolve into a self-trapped state with a donut-shaped profile, forming a vortex soliton carrying one unit of angular momentum. The atomic radial density profile nearly matches the stationary solution of the Gross Pitaevskii equation while displaying an instability azimuthally. At longer times or at more attractive interactions, the gas fragments into a ring of disjoint density blobs, resembling a necklace of bright solitons. We study this azimuthal instability by extracting the density power spectrum in different azimuthal modes and compare the observed quench dynamics with a simple prediction from a 2D modulational instability to find a condition for forming vortex solitons. Interestingly, the measured density power spectra collapse into a single behavior when the time is rescaled with respect to the interaction, thereby displaying a universal behavior for quench dynamics of a quantum vortex at attraction.