Ab initiomethods for finite-temperature two-dimensional Bose gases

The stochastic Gross-Pitaevskii equation and modified Popov theory are shown to provide an excellent ab initio description of finite-temperature, weakly interacting, two-dimensional Bose gas experiments. In particular, we demonstrate that the stochastic Gross-Pitaevskii equation generates excellent agreement with the recent experiment by C.-L. Hung et al. [Nature 470, 236 (2011)], thereby confirming that the observed universality and scale invariance arise naturally within this formalism. This is achieved in an ab initio manner, in which a systematic approach for obtaining a suitable value for the momentum cutoff of interacting classical field theories is proposed by means of the modified Popov theory.