Japanese explore quantum physics to create more efficient batteries

Recent headlines in specialized media have increasingly recorded important milestones in the application of quantum computers in scientific and technical work, but have you ever imagined that quantum physics could also be useful in the field of batteries? Researchers at the University of Tokyo are exploring quantum phenomena in an attempt to surpass the usefulness and capacity of conventional chemical batteries in certain low-energy applications.

Currently, researchers in various parts of the world are working on different aspects of quantum batteries – which store the energy of photons instead of electrons and ions, as in conventional electrochemical batteries – in laboratory experiments. In the case of the University of Tokyo’s Department of Information and Communication Engineering, graduate student Yuanbo Chen and associate professor Yoshihiko Kanagawa are investigating the best way to recharge a quantum battery. According to them, one of the advantages of quantum batteries is that they can be incredibly efficient, but this depends on how they are charged.

In the world of classical physics, to charge a battery using two chargers, this would have to be done in sequence, limiting the available options to just two possible orders. In standard quantum theory, the causal order of occurrence between events is prescribed and must be defined. This has been maintained until now in conventional quantum battery operating scenarios. In this study, the researchers went a step further by exploiting the quantum effect called indefinite causal order, or ICO, to charge quantum batteries using several chargers arranged in different orders, forming a quantum superposition.

In the classical domain, causality follows a clear path, meaning that if event A leads to event B, then the possibility of B causing A is ruled out. However, on the quantum scale, ICO allows for both directions of causality based on what is known as quantum superposition, making the two statements above simultaneously true.

In the Japanese experiment, in collaboration with the Beijing Computational Science Research Centre, various experiments were carried out to charge a quantum battery using optical devices such as lasers, lenses, and mirrors.

“With ICO, we have demonstrated that the way you charge a battery composed of quantum particles can significantly impact its performance,” explains Chen. “We observed huge gains in both the energy stored in the system and in thermal efficiency. And, somewhat counterintuitively, we discovered the surprising effect of an interaction that is the reverse of what you might expect: a lower power charger could deliver more energy more efficiently than a comparatively higher power charger using the same device,” adds the researcher.

According to the researchers, the ICO phenomenon explored in this study could find uses beyond recharging in a possible new generation of energy-efficient devices. It could improve the performance of other tasks involving thermodynamics or heat transfer. A promising example is solar panels which, under the effect of heat, today lose efficiency; ICO could be used to mitigate this effect, leading to efficiency gains.

The concept of quantum batteries, which introduces the possibility of creating efficient means of storing energy on a small scale, was first formally proposed 10 years ago by Robert Alicki, from the University of Gdańsk in Poland, and Mark Fannes, from KU Leuven in Belgium. The idea is to exploit microscopic dimensions and their non-classical characteristics, such as entanglement, in order to have batteries with more efficient and faster charging processes than the macroscopic world. Since then, much research has been done on the subject, examining different charging mechanisms, energy density and stability, among others, without, however, arriving at a commercial product.

Recharging time

A 2022 study quantified the maximum acceleration of a battery’s charging time that can be achieved through quantum effects. According to researchers from the Institute of Basic Sciences of the Republic of Korea, even with the growth of studies on quantum batteries with recharging speeds capable of surpassing their classical counterparts, a theoretical estimate of the size of this acceleration was lacking.

The research proved that the charging speed of quantum batteries can grow at most in quadratic proportion to the number of cells that make up the battery. In the case of classical batteries, this scale is linear, the reason for which stems from the fact that the cells are normally charged in parallel, which means that each cell is charged independently of the others. In quantum batteries, on the other hand, the charging protocol brings together multiple cells.