# Finite-size effects on the cluster expansions for quantum gases in restricted geometries

## TL;DR

This paper derives exact analytical expressions for the one-particle density matrices and quantum cluster expansions of ideal Bose and Fermi gases in restricted geometries, including effects of finite size and interactions, relevant for ultra-cold atom experiments.

## Contribution

It provides a comprehensive theoretical framework for finite-size effects on quantum gases in confined geometries, including a new theorem on quantum cluster integrals.

## Key findings

- Exact expressions for density matrices in 3D box and harmonic traps.
- Closed-form quantum cluster expansions for grand free energies.
- Analysis of short-ranged interactions in quasi 1-D systems.

## Abstract

We have analytically obtained 1-particle density matrices for ideal Bose and Fermi gases in both the 3-D box geometries and the harmonically trapped geometries for the entire range of temperature. We have obtained quantum cluster expansions of the grand free energies in closed forms for the same systems in the restricted geometries. We have proposed a theorem (with a proof) about the generic form of the quantum cluster integral. We also have considered short ranged interactions in our analyses for the quasi 1-D cases of Bose and Fermi gases in the box geometries. Our theoretical results are exact, and are directly useful for understanding finite-size effects on quantum cluster expansion of Bose and Fermi gases in the restricted geometries. Our results would be relevant in the context of experimental study of spatial correlations in ultra-cold systems of dilute Bose and Fermi gases of alkali atoms (i) in 3-D magneto-optical box traps with quasi-uniform potential around the center [1], and (ii) in 3-D harmonic traps [2, 3].