Diamonds have long been available in pairs—say, mounted in a nice set of earrings. Now physicists have managed to entangle the quantum states of two diamonds separated by 15 centimeters. Quantum entanglement is a phenomenon by which two or more objects share an unseen link bridging the space between them—a hypothetical pair of entangled dice, for instance, would always land on matching numbers, even if they were rolled in different places simultaneously. But that link is fragile, and for that reason entanglement experiments on physical systems usually take place in highly controlled laboratory setups—entangling, say, a pair of isolated atoms cooled to nearly absolute zero.
In the new study, scientists at the University of Oxford, the National Research Council of Canada and the National University of Singapore showed that entanglement could also be achieved in more ordinary objects at room temperature, in this case two different squares of synthetically produced diamond, each three millimeters across. The researchers split a laser beam in two and shone it through the diamonds; any photons that scattered off the diamond to generate a phonon, a quantum of vibrational energy, were funneled into a photon detector. The arrival of one of those photons signaled the presence of a vibration in the diamonds.
“We know that somewhere in that apparatus, there is one phonon,” says Ian Walmsley, an experimental physicist at Oxford and a co-author of the study. “But we cannot tell, even in principle, whether that came from the left-hand diamond or the right-hand diamond.” In quantum-mechanical terms, in fact, the phonon is not confined to either diamond. Instead the two diamonds enter an entangled state in which they share one phonon between them.
Walmsley notes that the diamonds are not perfect for quantum science—their entanglement is fleeting—but he hopes that investigators will consider using more ordinary materials in quantum technologies. “I think it gives a new scenario and a new instantiation of something that helps point in that direction,” he says.