Collective excitations of Bose-Einstein condensed gases at finite temperatures

TL;DR

This paper uses the Popov HFB approximation to calculate the finite-temperature excitation spectrum of a BEC of rubidium-87 atoms, showing good agreement with experiments at low temperatures but discrepancies near the phase transition.

Contribution

It applies the Popov HFB method to finite-temperature BEC excitations and compares results with experimental data, highlighting areas of agreement and disagreement.

Findings

Excellent agreement with experimental excitation spectra at low temperatures.

Discrepancies between theory and experiment near the BEC transition temperature.

Identifies limitations of the HFB-Popov approximation near critical temperature.

Abstract

We have applied the Popov version of the Hartree-Fock-Bogoliubov (HFB) approximation to calculate the finite-temperature excitation spectrum of a Bose-Einstein condensate (BEC) of $^{87}$Rb atoms. For lower values of the temperature, we find excellent agreement with recently-published experimental data for the JILA TOP trap. In contrast to recent comparison of the results of HFB--Popov theory with experimental condensate fractions and specific heats, there is disagreement of the theoretical and recent experimental results near the BEC phase transition temperature.