Such a quantum repeater uses groups of three photons for each bit of the message.

ECONOMIST: Quantum information technology

Dr Shields's photon detector, however, permits cryptographers to use a phenomenon called quantum entanglement to make a repeater that does not destroy quantum states.

ECONOMIST: Quantum information technology

But a traditional repeater destroys the quantum states of the photons, such as their planes of polarisation.

ECONOMIST: Quantum information technology