Simple scheme for extracting work with a single bath

TL;DR

This paper introduces a straightforward protocol for work extraction from a bipartite system using a single bath, demonstrating its effectiveness through models like two qubits and the Rabi model, with potential for cyclic energy transfer.

Contribution

It presents a new, simple protocol for work extraction leveraging thermalization, applicable to various quantum systems, and analyzes its efficiency and bounds.

Findings

Work extraction is maximized at finite bath temperatures.

Strong couplings enable extraction comparable to subsystem energies.

Work can be cyclically transferred to external devices at zero temperature.

Abstract

We propose a simple protocol exploiting the thermalization of a $\textit{storage}$ bipartite system $S$ to extract work from a $\textit{resource}$ system $R$. The protocol is based on a recent work definition involving only a single bath. A general description of the protocol is provided without specifying the characteristics of $S$. We quantify both the extracted work and the ideal efficiency of the process also giving maximum bounds for them. Then, we apply the protocol to two cases: two interacting qubits and the Rabi model. In both cases, for very strong couplings, an extraction of work comparable with the bare energies of the subsystems of $S$ is obtained and its peak is reached for finite values of the bath temperature, $T$. We finally show, in the Rabi model at $T=0$, how to transfer the work stored in $S$ to an external device, permitting thus a cyclic implementation of the whole work-extraction protocol. Our proposal makes use of simple operations not needing fine control.