Simon Fischer pursued his master's degree in Theoretical and Mathematical Physics at the Max Planck Institute for Physics and his PhD in Physics from the University of Cambridge. He studies quantum gases, quantum simulation, and thermalization.
Title: Weak wave turbulence as a precursor to universal coarsening in a homogeneous Bose gas
Abstract: Relaxation and condensation of an isolated low-energy Bose gas provide an ideal setting for the study of the universal features of far-from-equilibrium many-body dynamics and the emergence of long-range order. Here, we study particle transport during the relaxation of an isolated low-energy Bose gas from a far-from-equilibrium incoherent state towards a condensed state, and the late-time emergence of coherence. We first consider the initial stage of particle transport to low momenta, before the emergence of a condensate. In terms of the gas density n and interatomic s-wave scattering length a, we find that the time for incoherent particle transport is set by 1/(na)^2, in contrast to the collisional timescale 1/(na^2). We observe an inverse particle cascade with the momentum distribution developing a power-law tail with exponent γ≈2.4(1). Both of these observations are signatures of weak wave turbulence (WWT). We further study the subsequent growth of the condensate at low momenta through coarsening and show that it is accompanied by the decay of vortex excitations.
