Quantum Phase Diagram for Homogeneous Bose-Einstein Condensate

TL;DR

This paper maps the quantum phase diagram of a homogeneous Bose gas, revealing a reentrant transition where increased repulsion induces Bose-Einstein condensation above the critical temperature.

Contribution

It improves the calculation of the quantum phase transition by incorporating high-loop results and variational perturbation theory, revealing a reentrant transition in the phase diagram.

Findings

Reentrant transition above T_c^{(0)} where repulsion induces condensation

Enhanced accuracy in phase transition calculation using high-loop results

Prediction of a nose-shaped phase boundary in the diagram

Abstract

We calculate the quantum phase transition for a homogeneous Bose gas in the plane of s-wave scattering length a_s and temperature T. This is done by improving a one-loop result near the interaction-free Bose-Einstein critical temperature T_c^{(0)} with the help of recent high-loop results on the shift of the critical temperature due to a weak atomic repulsion using variational perturbation theory. The quantum phase diagram shows a nose above T_c^{(0)}, so that we predict the existence of a reentrant transition above T_c^{(0)}, where an increasing repulsion leads to the formation of a condensate.