Batteries that make use of quantum phenomena that appear to mock our conventional understanding of the laws of physics could be harnessed for energy storage. Although these batteries have only been produced on a small scale in laboratories, one day they might offer advantages over conventional batteries that could see them be the preferred choice in at least some niches.
From tiny medical devices to grid backups of variable energy sources, energy storage is one of the great challenges of our time. Quick and efficient charging is part of that. Despite quantum effects, by definition, taking place on the scale of the very small, University of Tokyo graduate student Yuanbo Chen is part of a team that hopes they could make a big difference to aspects of this problem.
“Current batteries for low-power devices, such as smartphones or sensors, typically use chemicals such as lithium to store charge, whereas a quantum battery uses microscopic particles like arrays of atoms,” Chen said in a . “While chemical batteries are governed by classical laws of physics, microscopic particles are quantum in nature, so we have a chance to explore ways of using them that bend or even break our intuitive notions of what takes place at small scales. I’m particularly interested in the way quantum particles can work to violate one of our most fundamental experiences, that of time.”
In classical physics, causality can only work one way – the cause comes before the effect. Even quantum physics, which so often refuses to be bound by what seem like unbreakable laws of physics usually appears to abide by this one. That is, to have any possibility of causing B, A needs to come before it.
However, Chen is part of a team that has shown it does not have to be that way. They have demonstrated it is possible to create a of a state where A comes before B, and therefore may plausibly cause it, and where B comes before A. This is an example of indefinite causal order (ICO).
This means that instead of a quantum battery being charged first by one charging device, and then by the other, it can be charged by a superposition of both. Moreover, when this is done, outcomes that normally need to be traded off against each other improve together. “Our results demonstrate that both the amount of energy charged and the thermal efficiency can be boosted simultaneously,” Chen and colleagues write.
“With ICO, we demonstrated that the way you charge a battery made up of quantum particles could drastically impact its performance,” Chen said. “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.”
To do this, the team used a quantum switch, which they write: “Can be considered as a device that accepts two channels as inputs, and depending on the state of the order qubit, outputs a superposition of channels in different causal orders.”
A great deal of our storage devices need to be portable, and the ICO system the team created certainly isn’t, relying on lasers reflected off beam-splitting mirrors and lenses to create their quantum effects. That’s not something you could, or would want to, put in your pocket. However, if there is anything our society has been good at in recent decades, it’s , and the team hope the same will be true of their work.
Better storage isn’t the only way the team thinks ICO could benefit the energy revolution. Solar panels get less efficient as they heat up, which has obvious problems for technology that needs to sit in direct sunlight. Most solutions involve placing solar cells above heat sinks, such as , but the team think they can use ICO to address the problem. Already, scientists have been working on quantum refrigerators that use ICO.
The study is published in .