Efficiency of optically pumping a quantum battery and a two-stroke heat engine

TL;DR

This paper investigates the efficiency of charging a quantum battery via optical pumping in a qutrit system and explores its application as a work fluid in a two-stroke thermal engine, highlighting the limits of efficiency.

Contribution

It introduces a model for quantum battery charging using optical pumping and analyzes its efficiency as a component of a quantum heat engine, including the maximum achievable efficiency.

Findings

Optical pumping effectively charges the quantum battery by creating a higher temperature reservoir.

The battery can be used as a work fluid in a two-stroke thermal machine with a defined efficiency limit.

The model demonstrates the potential for controlled energy storage and extraction in quantum systems.

Abstract

In this work, we study the efficiency of charging a quantum battery through optical pumping. The battery consists of a qutrit and it is connected to a natural thermal reservoir and an external coherent drive in the limit where its upper energy level can be adiabatically eliminated from the dynamics. In this scenario, the drive plus spontaneous emission optically pumps the intermediate energy level of the qutrit and the battery can be understood as being charged by an effective higher temperature reservoir that takes it out of equilibrium with the natural reservoir and stores useful energy in it. We also analyse the efficiency of using this battery and charging scheme as the work fluid of a two-stroke thermal machine. The thermal machine includes a fourth level through which work is extracted from the battery via a unitary transformation, therefore setting the limit of maximum efficiency of the machine.