Ordinary batteries lose charge like tea cools down. A quantum battery works differently: its heart is a tiny cavity with darting photons. If you illuminate it with special photon pairs, energy flows into a chain of qubit cells instantaneously — much like a swing gets a boost from strong pushes. These cells are made of materials that conduct current without loss (their properties were discovered by John Bardeen), and methods for controlling light in a cavity were perfected by Serge Haroche.
But fast charging is only half the battle. In ordinary carbon batteries, entropy grows (that is, disorder) and energy leaks away. Here, 'squeezed light' comes into play: it links photons so that losses are eliminated, as if the swing freezes at the top. The charge remains stable, like water in a thermos, and the system is unfazed by scratches or external jolts and noise.
Remarkably, squeezed light is already used in gravitational wave detectors to hear echoes of distant cataclysms. Perhaps the same principles will one day power drones or portable medical devices.
Squeezed light, which locks in charge, already helps physicists catch gravitational waves: it boosts measurement precision in detectors like LIGO, enabling them to pick up vibrations a quintillion times smaller than an atom.