Dynamics of an elementary quantum system in environments out of thermal equilibrium

TL;DR

This paper investigates how an elementary quantum system's dynamics are affected when placed near a body at a different temperature than its surroundings, revealing new control mechanisms for quantum states out of thermal equilibrium.

Contribution

It provides general formulas for the lifetime and density matrix of quantum systems near arbitrary bodies out of thermal equilibrium, and predicts phenomena like population inversion and cooling.

Findings

Population inversion can occur near a finite-thickness slab.

Quantum system's effective temperature can be much lower than involved temperatures.

Non-equilibrium environments enable new control over atomic states.

Abstract

We study the internal dynamics of an elementary quantum system placed close to a body held at a temperature different from that of the surrounding radiation. We derive general expressions for lifetime and density matrix valid for bodies of arbitrary geometry and dielectric permittivity. Out of equilibrium, the thermalization process and steady states become both qualitatively and quantitatively significantly different from the case of radiation at thermal equilibrium. For the case of a three-level atom close to a slab of finite thickness, we predict the occurrence of population inversion and an efficient cooling mechanism for the quantum system, whose effective internal temperature can be driven to values much lower than both involved temperatures. Our results show that non-equilibrium configurations provide new promising ways to control the state of an atomic system.