13 Fermi and Bose Gas at Non-zero Temperature

Franco Strocchi

Franco Strocchi

As an example of symmetry breaking at non-zero temperature we discuss the free Fermi and Bose gas, starting from finite volume and then discuss the thermodynamical limit.

Yiping Chen, Munekazu Horikoshi, Makoto Kuwata‐Gonokami +1 more

Experiments with ultracold atoms involve interatomic interactions, which are essential for cooling the atoms. The $s$-wave interaction between atoms can be tuned via the Feshbach resonance, potentially enabling the creation of a noninteracting system when the interaction reaches its vanishing limit. Although feasible at zero temperature, eliminating the interaction at a finite temperature in an isolated system prevents the system from reaching equilibrium. In this study, we used a Bose-Fermi mixture to create equilibrated noninteracting Bose gas at a finite temperature. First, we used the Bose-Fermi superfluid mixture of a dilute lithium gas in an optical dipole trap to determine the zero crossing of the boson-boson interaction at near-zero temperature. Thereafter, we showed that the noninteracting Bose gas created at a finite temperature represents an ideal Bose gas under the canonical description. The results of this study provides an avenue for experimental investigations of the fundamental properties of an ideal Bose gas in a harmonic trap.

Ye-Ryoung Lee, Jae Hyuk Choi, Caleb A. Christensen +4 more

Jan Dereziński, Ben Li, Marcin Napiórkowski

Abstract According to the Bogoliubov theory the low energy behaviour of the Bose gas at zero temperature can be described by non-interacting bosonic quasiparticles called phonons. In this work the damping rate of phonons at low momenta, the so-called Beliaev damping, is explained and computed with simple arguments involving the Fermi Golden Rule and Bogoliubov’s quasiparticles.