Emergence of a Turbulent Cascade in a Quantum Gas

TL;DR

This paper demonstrates the emergence of a turbulent cascade in a quantum Bose gas, combining experimental observations with numerical modeling, and highlights the system's potential for studying quantum turbulence phenomena.

Contribution

It provides the first experimental observation of a turbulent cascade in a homogeneous quantum Bose gas, supported by theoretical modeling using the Gross-Pitaevskii equation.

Findings

Observation of a power-law momentum distribution indicating a turbulent cascade

Excellent agreement between experimental data and GPE simulations

Establishment of a homogeneous Bose gas as a platform for turbulence studies

Abstract

In the modern understanding of turbulence, a central concept is the existence of cascades of excitations from large to small lengthscales, or vice-versa. This concept was introduced in 1941 by Kolmogorov and Obukhov, and the phenomenon has since been observed in a variety of systems, including interplanetary plasmas, supernovae, ocean waves, and financial markets. Despite a lot of progress, quantitative understanding of turbulence remains a challenge due to the interplay of many lengthscales that usually thwarts theoretical simulations of realistic experimental conditions. Here we observe the emergence of a turbulent cascade in a weakly interacting homogeneous Bose gas, a quantum fluid that is amenable to a theoretical description on all relevant lengthscales. We prepare a Bose-Einstein condensate (BEC) in an optical box, drive it out of equilibrium with an oscillating force that pumps energy into the system at the largest lengthscale, study the BEC's nonlinear response to the periodic drive, and observe a gradual development of a cascade characterised by an isotropic power-law distribution in momentum space. We numerically model our experiments using the Gross-Pitaevskii equation (GPE) and find excellent agreement with the measurements. Our experiments establish the uniform Bose gas as a promising new platform for investigating many aspects of turbulence, including the interplay of vortex and wave turbulence and the relative importance of quantum and classical effects.