Charge-Preserving Operations in Quantum Batteries

TL;DR

This paper introduces ergotropy-preserving operations and isoergotropic states to optimize energy storage and management in quantum batteries, with practical implications for charging protocols and charge retention.

Contribution

It formalizes ergotropy-preserving operations and isoergotropic states, demonstrating their role in redistributing energy components in quantum systems and their implementation via beam-splitter interactions.

Findings

Ergotropy-preserving operations can redistribute coherent and incoherent energy components.

These operations can be implemented through beam-splitter-type interactions.

Isoergotropic states help optimize charging protocols and reduce charge loss.

Abstract

Ergotropy provides a fundamental measure of the extractable work from a quantum system and, consequently, of the maximal useful energy, or charge, stored within it. Understanding how this quantity can be manipulated and transformed efficiently is crucial for advancing quantum energy management technologies. Here, we introduce and formalize the concepts of isoergotropic states and ergotropy-preserving operations, which reorganize the internal structure of ergotropy while keeping its total value unchanged. These ideas are illustrated for both discrete (two-level systems) and continuous-variable systems (single-mode Gaussian states). In each case, we show how ergotropy-preserving operations redistribute the respective coherent-incoherent and displacement-squeezing components. We further examine the thermodynamic exchanges accompanying ergotropy-preserving operations, including variations in energy and entropy, and demonstrate that these transformations can be dynamically implemented through standard beam-splitter-type interactions with an auxiliary system. Finally, we discuss the practical implications of isoergotropic states and operations in optimizing charging protocols and mitigating charge loss in open quantum batteries.