Light from an ordinary bulb is a stream of individual photons, like drops from a faucet. But there is also light where photons come in pairs, like twins walking together. Such grouped light has long been desired for measuring distances and imaging objects hidden around corners. But sources of this light were either too dim, or their flashes too short for ordinary detectors to catch.
Researchers have found a way to turn ordinary light into grouped light with an efficiency a billion times higher than previous methods. They pass light through a special medium that forces photons to pair up, with almost no loss of brightness. Previously, such conversion lost almost all the energy, but now losses are minimal.
Such bright grouped light can be used in rangefinders, for clock synchronization, and for imaging hidden objects. The technology becomes practical: now there is enough brightness and signal duration for ordinary detectors to register it.
Photons in grouped light come in pairs, as if holding hands — a quantum effect that does not occur in the classical world.