The battery capacity of energy-storing quantum systems

TL;DR

This paper introduces the concept of quantum battery capacity as a measure of a quantum system's energy storage potential, linking it to entropy, coherence, and entanglement, and distinguishing it from ergotropy.

Contribution

It defines quantum battery capacity as a new figure of merit, expanding understanding of energy storage in quantum systems beyond existing measures.

Findings

Quantum battery capacity is related to entropy, coherence, and entanglement.

It differs from ergotropy by not depending on the system's temporary energy level.

The capacity provides a new way to quantify energy storage potential in quantum systems.

Abstract

The quantum battery capacity is introduced in this letter as a figure of merit that expresses the potential of a quantum system to store and supply energy. It is defined as the difference between the highest and the lowest energy that can be reached by means of the unitary evolution of the system. This function is closely connected to the ergotropy, but it does not depend on the temporary level of energy of the system. The capacity of a quantum battery can be directly linked with the entropy of the battery state, as well as with measures of coherence and entanglement.