Work extraction from coherently activated maps via quantum switch

TL;DR

This paper investigates how quantum-controlled ordering of maps via the quantum switch can enhance work extraction from quantum systems, showing non-negative ergotropy gains and conditions for positive work extraction.

Contribution

It introduces a framework for analyzing work extraction using quantum switch-activated maps, revealing conditions for positive ergotropic gains and demonstrating practical examples.

Findings

Quantum switch application always yields non-negative ergotropy gain.

Conditions identified for achieving non-zero ergotropic gain.

Work can be extracted from thermalized systems with coherently controlled reservoirs.

Abstract

We characterize the impact that the application of two maps in a quantum-controlled order has on the process of work extraction via unitary cycles and its optimization. The control is based on the quantum switch model that applies maps in an order not necessarily compatible with the underlying causal structure and, in principle, can be implemented experimentally. First, we show that the activation of quantum maps through the quantum switch model always entails a non-negative gain in ergotropy compared to their consecutive application. We also establish a condition that the maps should fulfill in order to achieve a non-zero ergotropic gain. We then perform a thorough analysis of maps applied to a two-level system and provide general conditions for achieving a positive gain on the incoherent part of ergotropy. Our results are illustrated with several examples and applied to qubit and $d$-dimensional quantum systems. In particular, we demonstrate that a non-zero work can be extracted from a system thermalized by two coherently controlled reservoirs.