Physicists in the UK have succeeded in routing and teleporting entangled states of light between two four-user quantum networks – an important milestone in the development of scalable quantum communications. Led by Mehul Malik and Natalia Herrera Valencia of Heriot-Watt University in Edinburgh, Scotland, the team achieved this milestone thanks to a new method that uses light-scattering processes in an ordinary optical fibre to program a circuit. This approach, which is radically different from conventional methods based on photonic chips, allows the circuit to function as a programmable entanglement router that can implement several different network configurations on demand. The team performed the experiments using commercially-available optical fibres, which are multi-mode structures that scatter light via random linear optical processes. In simple terms, Herrera Valencia explains that this means the light tends to ricochet chaotically through the fibres along hundreds of internal pathways.…