Charging by quantum measurement

TL;DR

This paper introduces a quantum charging method using measurements on ancillary qubits, enabling efficient energy transfer and state manipulation of a quantum battery without initial coherence, highlighting the role of measurement in nonequilibrium quantum systems.

Contribution

The study presents a measurement-based quantum charging scheme that surpasses traditional methods by utilizing projective measurements to transfer energy and enhance ergotropy without requiring initial coherence.

Findings

Near-perfect energy transfer via optimized measurements

High ergotropy achievable from thermal states with fewer than N measurements

Measurement operations outperform non-measurement charging methods

Abstract

We propose a quantum charging scheme fueled by measurements on ancillary qubits serving as disposable chargers. A stream of identical qubits are sequentially coupled to a quantum battery of $N+1$ levels and measured by projective operations after joint unitary evolutions of optimized intervals. If charger qubits are prepared in excited state and measured on ground state, then their excitations (energy) can be near-perfectly transferred to battery by iteratively updating the optimized measurement intervals. Starting from its ground state, the battery could be constantly charged to an even higher energy level. Starting from a thermal state, the battery could also achieve a near-unit ratio of ergotropy and energy through less than $N$ measurements, when a population inversion is realized by measurements. If charger qubits are prepared in ground state and measured on excited state, useful work extracted by measurements alone could transform the battery from a thermal state to a high-ergotropy state before the success probability vanishes. Our operations in charging are more efficient than those without measurements and do not invoke the initial coherence in both battery and chargers. Particularly, our finding features quantum measurement in shaping nonequilibrium systems.