Strong interaction induced dimensional crossover in 1D quantum gas

TL;DR

This study investigates how strong interactions induce a dimensional crossover from 1D to 3D in a quantum gas, revealing the limitations of existing theories and identifying a universal crossover regime.

Contribution

It demonstrates the breakdown of 1D theories under strong interactions and introduces a modified Yang-Yang equation to describe the system beyond the 1D threshold.

Findings

Strong interactions cause the 1D quantum gas to become effectively 3D.

Standard 1D theories fail under strong interactions, but a modified Yang-Yang equation provides better description.

Identified a universal crossover regime where both 1D and 3D hydrodynamics fail.

Abstract

We generated a one-dimensional quantum gas confined in an elongated optical dipole trap instead of 2D optical lattices. The sample, comprising thousands of atoms, spans several hundred micrometers and allows for independent control of temperature and chemical potential using Feshbach resonance. This allows us to directly observe and investigate the spatial distribution and associated excitation of 1D quantum gas without any ensemble averaging. In this system, we observed that the dimension of 1D gas will be popped up into 3D due to strong interaction without changing any trapping confinement. During the dimensional crossover, we found that increasing the scattering length leads to the failure of 1D theories, including 1D mean field, Yang-Yang equation, and 1D hydrodynamics. Specifically, the modified Yang-Yang equation effectively describes this 1D system at temperatures beyond the 1D threshold, but it does not account for the effects of stronger interactions. Meanwhile, we observe two possible quantized plateaus of breathing-mode oscillation frequencies predicted by 1D and 3D hydrodynamics, corresponding to weak and strong interactions respectively. And there is also a universal crossover connecting two different regimes where both hydrodynamics fail.