Two clouds of atoms that store quantum information, called quantum memories, have been connected across a longer distance than ever before. They could prove useful for building a quantum version of the internet
Quantum communication relies on a phenomenon called entanglement. When a pair of particles or systems are quantum entangled, measuring one of them instantly influences the measured state of the other, regardless of the distance between them.
These connections can’t directly transfer information, because that would mean information is travelling faster than light, but entanglement can be used to create encrypted communications channels, secured against hacking by the laws of quantum physics.
Individual photons have been entangled across distances exceeding 1000 kilometres, but for larger systems of particles, which hold more information, maintaining this entanglement is harder. The maximum distance between a pair of entangled quantum memories so far is just 1.3 kilometres.
Xiao-Hui Bao at the University of Science and Technology of China and his colleagues have now smashed that record, entangling two quantum memories over 22 kilometres of fibre-optic cable installed underground.