[Paper Review] Colloquium: Quantum Batteries

Francesco Campaioli, Stefano Gherardini+3 more|arXiv (Cornell University)|Aug 4, 2023

Advanced battery technologies research261 references11 citations

TL;DR

A pedagogical review of quantum batteries detailing theoretical framework, models of many-body batteries, charging protocols, open-system effects, and experimental platforms. It highlights ergotropy, passive states, quantum advantage, and bounds on charging power.

ABSTRACT

Recent years have witnessed an explosion of interest in quantum devices for the production, storage, and transfer of energy. In this Colloquium, we concentrate on the field of quantum energy storage by reviewing recent theoretical and experimental progress in quantum batteries. We first provide a theoretical background discussing the advantages that quantum batteries offer with respect to their classical analogues. We then review the existing quantum many-body battery models and present a thorough discussion of important issues related to their open nature. We finally conclude by discussing promising experimental implementations, preliminary results available in the literature, and perspectives.

Motivation & Objective

• Present a theoretical framework for quantum batteries and define key quantities like ergotropy and passive states.
• Survey unitary charging and work extraction protocols and their bounds within open and closed systems.
• Analyze charging power, quantum speed limits, and conditions for quantum advantage in multi-partite batteries.
• Review prominent many-body battery models and their charging properties, including Dicke and spin-chain batteries.
• Discuss experimental implementations and outlook for quantum battery technologies.

Proposed method

• Define the internal Hamiltonian H0 and the charging Hamiltonian H1 and describe unitary evolution as the mechanism for charging.
• Introduce ergotropy as the maximal extractable work under unitary operations and passive states as those from which no work can be extracted.
• Present bounds on extractable/injectable work and their relation to complete passivity and thermal states.
• Discuss charging power, average vs instantaneous power, and quantum speed limits as limits on charging rates.
• Characterize quantum advantage through power scaling and compare local versus global charging schemes.
• Review interaction order effects and derive bounds on achievable quantum advantage with k-body interactions.

Experimental results

Research questions

• RQ1 What are the fundamental limits on work extraction and energy storage in quantum batteries under unitary dynamics?
• RQ2 How do passive states, ergotropy, and complete passivity constrain charging and discharging processes?
• RQ3 Under what conditions can quantum batteries achieve a power advantage over classical counterparts, and what role do entanglement and correlations play?
• RQ4 How does the interaction order (k-body) constrain the scaling of charging power in many-body batteries?
• RQ5 What are the key experimental platforms and protocols that realize quantum batteries and test theoretical bounds?

Key findings

• Ergotropy provides a tight bound on extractable work from a quantum battery under unitary evolution.
• Completely passive states are thermal, and for N copies, ergotropy per copy approaches a bound set by thermal comparison states in the large-N limit.
• Global (collective) charging can achieve N-fold speed-up in charging time versus local charging, indicating a quantum advantage.
• Entanglement is not strictly necessary for power advantage, as shown by protocols with no entanglement but reduced total work exchanged, though entanglement often enhances both work and power.
• The achievable quantum advantage is bounded by interaction order, with k-body limitations constraining scalability of power gains.
• Quantum speed limits provide fundamental bounds on charging time and thus on achievable average power.