Quantum Batteries Could be Weird in a Good Way

Lab curiosity for now. But wait a few femtoseconds.

We might get this before we get fusion reactors.

You’re late for an important appointment. Just as you are leaving your house, you realise your phone is flat.

Imagine you could charge it almost instantly by exploiting the strange rules of quantum physics. That’s the promise of quantum batteries.

My colleagues and I at CSIRO have developed the world’s first quantum battery prototypes – and the direction the technology has taken is surprising.

You may have heard of the peculiar quantum effects of superposition and entanglement, which allow mostly very tiny objects to behave very strangely. They could also allow quantum computers to solve problems conventional computers cannot.

One strange feature of the quantum world is what are called “collective effects”. They are what give quantum batteries their unique properties.

Under the right circumstances, the storage units of quantum batteries don’t act individually, but behave collectively. In a counterintuitive twist, this means the units charge faster together than if they were charging alone.

Let’s say your quantum battery has N storage units, and each unit takes one second to charge. Collective effects mean that if all units are charged at once, each unit will take only 1∕√N seconds to charge.

This means that the bigger your quantum battery, the less time it takes to charge. If it doubles in size, charging will take just a little more than half as long.

It is as if each unit somehow knows there are other units around, and their presence makes the unit charge faster. Strange, right?

This is radically different from how conventional batteries work, where bigger batteries typically take longer to charge. That’s why it might take an hour to charge your mobile phone, but your electric car needs all night.

The idea of a quantum battery was just a theoretical curiosity for a long time. But back in 2018, I set out to demonstrate that they could actually be built.

In 2022, working with colleagues in the United Kingdom and Italy, we built a quantum battery prototype using an organic microcavity – a kind of tiny, complicated multi-layer sandwich of several different materials that traps light in a particular way.

And we were able to show for the first time the exotic behaviour where larger quantum batteries really do take less time to charge.

In fact, we were able to demonstrate that the charging time decreases as 1∕√N, where N was the number of molecules in our battery. The more molecules we included, the faster the battery charged — exactly as theory had predicted.

One thing this first prototype didn’t have was a way to extract the energy out of it. To do this, in our latest study, published in the journal Light: Science & Applications, we added extra layers into our device that converted the energy into an electrical current. This marks a major step towards a practical quantum battery.