Laser Cooling Beyond Rate Equations: Approaches From Quantum Thermodynamics
Abstract
Solids can be cooled by driving impurity ions with lasers, allowing them to transfer heat from the lattice phonons to the electromagnetic surroundings. This exemplifies a quantum thermal machine, which uses a quantum system as a working medium to transfer heat between reservoirs. We review the derivation of the Bloch-Redfield equation for a quantum system coupled to a reservoir, and its extension, using counting fields, to calculate heat currents. We use the full form of this equation, which makes only the weak-coupling and Markovian approximations, to calculate the cooling power for a simple model of laser cooling. We compare its predictions with two other time-local master equations: the secular approximation to the full Bloch-Redfield equation, and the Lindblad form expected for phonon transitions in the absence of driving. We conclude that the full Bloch-Redfield equation provides accurate results for the heat current in both the weak- and strong- driving regimes, whereas the other forms have more limited applicability. Our results support the use of Bloch-Redfield equations in quantum thermal machines, in spite of their potential to give unphysical results.
Cite
@article{arxiv.2201.07132,
title = {Laser Cooling Beyond Rate Equations: Approaches From Quantum Thermodynamics},
author = {C. N. Murphy and L. Toledo Tude and P. R. Eastham},
journal= {arXiv preprint arXiv:2201.07132},
year = {2022}
}
Comments
13 pages