Observation of universal behaviour of ultracold quantum critical gases

TL;DR

This paper reports the experimental observation of a universal exponential density probability distribution in ultracold quantum critical Bose gases, revealing combined phase fluctuation effects near the BKT transition in a 1D optical lattice.

Contribution

It demonstrates the universal behavior of density fluctuations in quantum critical Bose gases, integrating experimental results with a simple theoretical model.

Findings

Universal exponential density distribution observed experimentally.

Phase fluctuations coexist in the quantum critical region.

Theoretical model agrees with experimental data.

Abstract

Quantum critical matter has already been studied in many systems, including cold atomic gases. We report the observation of a universal behaviour of ultracold quantum critical Bose gases in a one-dimensional optical lattice. In the quantum critical region above the Berezinskii-Kosterlitz-Thouless transition, the relative phase fluctuations between neighboring subcondensates and spatial phase fluctuations of quasi-2D subcondensates coexist. We study the density probability distribution function when both these two phase fluctuations are considered. A universal exponential density probability distribution is demonstrated experimentally, which agrees well with a simple theoretical model by considering these two phase fluctuations.