Quantum batteries could charge more efficiently by skirting conventional rules of causality.

Yuanbo Chen at the University of Tokyo and his colleagues analysed whether a particularly counterintuitive quantum phenomenon could play a role in powering quantum batteries – energy storage devices that could harness quantum effects.

In the classical world, causality goes in just one direction: if event A causes event B, then it is clear that B did not also cause A. But at the quantum scale, Chen says that it …