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arXiv · 2401.15540

The Second Order 2D Behaviors of a 3D Bose Gases in the Gross-Pitaevskii Regime

Xuwen Chen·Jiahao Wu·Zhifei Zhang
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Abstract

We consider a system of $N$ bosons interacting in a three-dimensional box endowed with periodic boundary condition that is strongly confined in one direction such that the normalized thickness of the box $d\ll1$. We assume particles to interact through a repulsive, radially symmetric and short-range interaction potential with scattering length scale $a\ll d$. We present a comprehensive study of such system in the Gross-Pitaevskii regime, up to the second order ground state energy, starting from proving optimal Bose-Einstein condensation results which were not previously available. The fine interplay between the parameters $N$, $a$ and $d$ generates three regions. Our result in one region on the one hand, is compatible with the classical three-dimensional Lee-Huang-Yang formula. On the other hand, it reveals a new mechanism exhibiting how the second order correction compensates and modifies the first order energy, which was previously thought of as containing a jump, and thus explains how a three-dimensional Bose gas system smoothly transits into two-dimensional system. Moreover, delving into the analysis of this new mechanism exclusive to the second order, we discover a dimensional coupling correlation effect, deeply buried away from the expected 3D and quasi-2D renormalizations, and calculate a new second order correction to the ground state energy.

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Xuwen Chen, Jiahao Wu, Zhifei Zhang. 2025-06-29. The Second Order 2D Behaviors of a 3D Bose Gases in the Gross-Pitaevskii Regime. https://doi.org/10.1090/cams%2F79

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