Thermodynamics of relativistic quantum fields confined in cavities

TL;DR

This paper explores the thermodynamic behavior of relativistic quantum fields in cavities, analyzing energy transfer efficiency, work extraction, and the influence of initial states, with applications to gravitational waves and Bose-Einstein condensates.

Contribution

It provides a detailed analysis of energy transfer and work extraction in relativistic quantum fields, highlighting the role of initial states and cavity types, including Bose-Einstein condensates.

Findings

Efficiency depends on initial quantum state.

Energy transfer to phonons approaches unity in BECs.

Work extraction is more efficient with trapped Bose-Einstein condensates.

Abstract

We investigate the quantum thermodynamical properties of localised relativistic quantum fields, and how they can be used as quantum thermal machines. We study the efficiency and power of energy transfer between the classical gravitational degrees of freedom, such as the energy input due to the motion of boundaries or an impinging gravitational wave, and the excitations of a confined quantum field. We find that the efficiency of energy transfer depends dramatically on the input initial state of the system. Furthermore, we investigate the ability of the system to extract energy from a gravitational wave and store it in a battery. This process is inefficient in optical cavities but is significantly enhanced when employing trapped Bose Einstein condensates. We also employ standard fluctuation results to obtain the work probability distribution, which allows us to understand how the efficiency is related to the dissipation of work. Finally, we apply our techniques to a setup where an impinging gravitational wave excites the phononic modes of a Bose Einstein condensate. We find that, in this case, the percentage of energy transferred to the phonons approaches unity after a suitable amount of time. These results give a quantitative insight into the thermodynamic behaviour of relativistic quantum fields confined in cavities.