Interaction-induced 1D-3D dimensional crossover

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