Universal quench dynamics in attractive two-dimensional Bose gases

We experimentally study universal non-equilibrium dynamics of homogeneous two-dimensional (2D) Bose gases quenched from repulsive to attractive interactions. We show that the interaction quench induces an instability that stimulates emission of quasiparticle pairs from a degenerate 2D gas. Using in situ density noise measurements, we present direct characterization of coherence and quantum entanglement between interaction quench generated quasiparticles. Moreover, we show that the initial quasiparticle emission and instability eventually lead to amplified density waves and fragmentation of a 2D sample. We observe formation of 2D matter-wave Townes solitons that were previously considered impossible to prepare in equilibrium. Our studies unveil a set of scale-invariant and universal scaling behaviors in the quench dynamics. We further discuss how our experimental platform could be extended to explore non-equilibrium physics and observe intricate many-body effects such as quantum critical transport in a homogenous quantum gas.