So far physicists have developed a form of secure encryption, known as quantum key distribution, in which particles of light, called photons, are transmitted. The process allows two parties to share, without risk of interception, a secret key used to encrypt and decrypt information. But to date this technique has only been effective between two users.
"Until now efforts to expand the network have involved vast infrastructure and a system which requires the creation of another transmitter and receiver for every additional user. Sharing messages in this way, known as trusted nodes, is just not good enough because it uses so much extra hardware which could leak and would no longer be totally secure," Dr Joshi said.
The team's technique applies the principle of entanglement, which Albert Einstein described as 'spooky action at a distance. It exploits the power of two different particles placed in separate locations, potentially thousands of miles apart, to simultaneously mimic each other. This process presents far greater opportunities for quantum computers, sensors, and information processing.
"Instead of having to replicate the whole communication system, this latest methodology, called multiplexing, splits the light particles, emitted by a single system, so they can be received by multiple users efficiently," Dr Joshi said.
The team created a network for eight users using just eight receiver boxes, whereas the former method would need the number of users multiplied many times — in this case, amounting to 56 boxes. As the user numbers grow, the logistics become increasingly unviable — for instance 100 users would take 9,900 receiver boxes.