Nonthermal fixed points, vortex statistics, and superfluid turbulence in an ultracold Bose gas

TL;DR

This paper investigates nonthermal fixed points and vortex dynamics in ultracold Bose gases, revealing universal scaling laws and their relation to superfluid turbulence, with implications for experiments and fundamental physics.

Contribution

It provides a detailed analysis of nonthermal fixed points, vortex statistics, and turbulence in Bose gases, connecting wave turbulence theory with vortex excitations and experimental observability.

Findings

Universal power-law distributions linked to vortex dynamics.

Scaling exponents consistent with conservation laws.

Vortex-antivortex pairing explains long-time dynamics.

Abstract

Nonthermal fixed points of the dynamics of a dilute degenerate Bose gas far from thermal equilibrium are analyzed in two and three spatial dimensions. Universal power-law distributions, previously found within a nonperturbative quantum-field theoretical approach and recently shown to be related to vortical dynamics and superfluid turbulence [Phys. Rev. B 84, 020506(R) (2011)], are studied in detail. The results imply an interpretation of the scaling behavior in terms of independent vortex excitations of the superfluid and show that the statistics of topological excitations can be described in the framework of wave turbulence. The particular scaling exponents observed in the single-particle momentum distributions are found to be consistent with irreversibility as well as conservation laws obeyed by the wave interactions. Moreover, long-wavelength acoustic excitations of the vortex-bearing condensate, driven by vortex annihilations, are found to follow a nonthermal power law. Considering vortex correlations in a statistical model, the long-time departure from the nonthermal fixed point is related to vortex-antivortex pairing. The studied nonthermal fixed points are accessible in cold-gas experiments. The results shed light on fundamental aspects of superfluid turbulence and have strong potential implications for related phenomena, e.g., in early-universe inflation or quark-gluon plasma dynamics.