Quantum Batteries: Unleashing the Groundbreaking Potential in Breaking Causality

Quantum batteries, featuring innovative charging procedures, signify a significant advancement in battery technology, offering greater effectiveness and a broader range of uses in sustainable energy solutions.

A novel method of charging batteries utilises the concept of “indefinite causal order.”

Quantum batteries, which use quantum phenomena to produce, distribute, and store energy, are expected to surpass traditional chemical batteries' capabilities and usefulness in certain low-power applications. Researchers, including those from the University of Tokyo, have for the first time exploited a quantum process that defies the conventional view of causality to enhance quantum batteries' performance, nudging this futuristic technology a little closer to reality.

When it comes to the term "quantum," which governs subatomic world physics, quantum computer developments tend to get the most attention. However, other emerging quantum technologies are worth noting. Among them is the quantum battery, which, despite its initially perplexing name, offers untapped potential for sustainable energy solutions and possible incorporation into future electric vehicles. Regardless, these novel devices are expected to find use in diverse portable and low-power applications, particularly in situations where recharging opportunities are limited.

In a classical sense, charging a battery with two chargers would have to be sequential, limiting the options to just two possible sequences. However, taking advantage of a unique quantum effect called ICO enables quantum batteries to be charged in an unusually nonconventional manner. Here, multiple chargers organised in various sequences can coexist, creating a quantum superposition.

Currently, quantum batteries only exist as lab experiments, and worldwide researchers are exploring various components that they hope will eventually merge into a fully functional and practical application. Graduate student Yuanbo Chen and Associate Professor Yoshihiko Hasegawa from the University of Tokyo's Department of Information and Communication Engineering are studying the most effective method to charge a quantum battery. The way these batteries are charged is a crucial factor affecting their incredible efficiency.

Chen remarks that current low-power device batteries, such as those for smartphones or sensors, typically employ chemicals like lithium for charge storage enquanto quantum batteries use microscopic components like atomic arrays. Chemical batteries operate according to classical physics laws, while microscopic particles are quantum in nature, providing an opportunity to explore unconventional utilisation methods that challenge or even defy our intuitive understanding of small-scale activities. Chen is particularly interested in how quantum particles can challenge our basic understanding of time.

Although it's considerably larger than a typical household AA battery, the experimental device acting as a quantum battery displayed charging traits that could eventually improve the battery in your smartphone.

In collaboration with researcher Gaoyan Zhu and Professor Peng Xue from the Beijing Computational Science Research Center, the team experimented with charging a quantum battery using optical equipment such as lasers, lenses, and mirrors. The methods necessitated a quantum effect implying a lack of causal connection between events, unlike what we experience in our day-to-day lives. Earlier procedures for charging a quantum battery involved sequential charging stages, but the team used a novel quantum effect they term indefinite causal order (ICO). While causality follows a clear path in the classical world, preventing a reaction from its cause, ICO in the quantum world allows causality to occur in both directions simultaneously.

Normally, we would assume that a stronger battery charger results in a battery with a stronger charge. However, the discovery linked to ICO suggests an astonishing reversal in this correlation; it is now possible to charge a more energetic battery with significantly less power.

“With ICO, we demonstrated that the way you charge a battery made up of quantum particles could drastically impact its performance,” said Chen. “We saw huge gains in both the energy stored in the system and the thermal efficiency. And somewhat counterintuitively, we discovered the surprising effect of an interaction that’s the inverse of what you might expect: A lower-power charger could provide higher energies with greater efficiency than a comparably higher-power charger using the same apparatus.”

The phenomenon of ICO the team explored could find uses beyond charging a new generation of low-power devices. The underlying principles, including the inverse interaction effect uncovered here, could improve the performance of other tasks involving thermodynamics or processes that involve the transfer of heat. One promising example is solar panels, where heat effects can reduce their efficiency, but ICO could be used to mitigate those and lead to gains in efficiency instead.

Reference: “Charging Quantum Batteries via Indefinite Causal Order: Theory and Experiment” by Gaoyan Zhu, Yuanbo Chen, Yoshihiko Hasegawa and Peng Xue, 13 December 2023, Physical Review Letters. DOI: 10.1103/PhysRevLett.131.240401

This work has been supported by the National Natural Science Foundation of China (Grant Nos. 92265209 and 12025401). Y. H. acknowledges support by JSPS KAKENHI Grant Number JP22H03659. Y.C. acknowledges support by JST SPRING, Grant Number JPMJSP2108.