Collective excitations of a dilute Bose gas at finite temperature: TDHFB Theory

TL;DR

This paper employs the TDHFB approach to analyze the equilibrium and dynamical properties of a finite-temperature Bose gas, highlighting the effects of anomalous correlations and comparing results with Quantum Monte Carlo simulations.

Contribution

It introduces a comprehensive TDHFB framework for finite-temperature Bose gases, including anomalous correlations, and applies it to both uniform and trapped systems.

Findings

Derived expressions for excitation spectra and superfluid fraction.

Quantitative agreement with Quantum Monte Carlo simulations.

Explained anomalous behavior of the m=0 mode in experiments.

Abstract

Using the time-dependent Hartree-Fock-Bogoliubov approach, where the condensate is coupled with the thermal cloud and the anomalous density, we study the equilibrium and the dynamical properties of three-dimensional quantum-degenerate Bose gas at finite temperature. Effects of the anomalous correlations on the condensed fraction and the critical temperature are discussed. In uniform Bose gas, useful expressions for the Bogoliubov excitations spectrum, the first and second sound, the condensate depletion and the superfluid fraction are derived. Our results are tested by comparing the findings computed by Quantum Monte Carlo simulations. We present also a systematic investigation of the collective modes of a Bose condensate confined in an external trap. Our predictions are in qualitative agreement with previous experimental and theoretical results. We show in particular that our theory is capable of explaining the so-called anomalous behavior of the m=0 mode.