An entangled-LED-driven quantum relay over 1 km

Quantum cryptography allows confidential information to be communicated between two parties, with secrecy guaranteed by the laws of nature alone. However, upholding guaranteed secrecy over networks poses a further challenge, as classical receive-and-resend routing nodes can only be used conditional of trust by the communicating parties, which arguably diminishes the value of the underlying quantum cryptography. Quantum relays offer a potential solution by teleporting qubits from a sender to a receiver, without demanding additional trust from end users. Here we demonstrate the operation of a quantum relay over 1 km of optical fibre, which teleports a sequence of photonic quantum bits to a receiver by utilising entangled photons emitted by a semiconductor light-emitting diode. The average relay fidelity of the link is 0.90±0.03, exceeding the classical bound of 0.75 for the set of states used, and sufficiently high to allow error correction. The fundamentally low multiphoton emission statistics and the integration potential of the source present an appealing platform for future quantum networks. A quantum relay harnessing coupled photons from a light-emitting diode removes the need for insecure routing nodes in quantum cryptography. The device developed by Mark Stevenson from Toshiba Research Europe Limited and his colleagues creates photons that are entangled; that is, they share quantum properties even when they are far apart. These two photons, when divided between the sender and receiver of a message, enable a security key to be safely shared. Sending optical signals over long distances usually requires additional systems called nodes to boost the signal or split it to multiple receivers. Such nodes pose a security risk as they could be used by an eavesdropper to intercept the message. The electrically driven quantum relay circumvents this security risk and enables communication over a one kilometer optical fiber.