Optimal work extraction from quantum states by photo-assisted Cooper pair tunneling

TL;DR

This paper demonstrates a realistic superconducting circuit engine capable of optimally extracting work from quantum states, including Gaussian and Fock states, by leveraging phase coherence and photo-assisted Cooper pair tunneling.

Contribution

It introduces a practical superconducting circuit model that achieves optimal quantum work extraction, bridging theoretical bounds with experimental feasibility.

Findings

Maximal work extraction from Gaussian and Fock states achieved

Coherence enhances power output of the quantum engine

Engine operates effectively with a stabilized oscillator state

Abstract

The theory of quantum thermodynamics predicts fundamental bounds on work extraction from quantum states. As these bounds are derived in a very general and abstract setting, it is unclear how relevant they are in an experimental context, where control is typically limited. Here we address this question by showing that optimal work extraction is possible for a realistic engine. The latter consists of a superconducting circuit, where a LC-resonator is coupled to a Josephson junction. The oscillator state fuels the engine, providing energy absorbed by Cooper pairs, thus producing work in the form of an electrical current against an external voltage bias. We show that this machine can extract the maximal amount of work from all Gaussian and Fock states. Furthermore, we consider work extraction from a continuously stabilized oscillator state. In both scenarios, coherence between energy eigenstates is beneficial, increasing the power output of the machine. This is possible because the phase difference across the Josephson junction provides a phase reference.