A quantum memory for photons that works at room temperature has been created by physicists in the UK. The breakthrough could help researchers to develop a quantum repeater device that allow quantum information to be transmitted over long distances.
Quantum bits (or qubits) of information can be transmitted using photons and put to use in a number of applications, including cryptography. These schemes rely on the fact that photons can travel relatively long distances without interacting with their environment. This means that photon qubits are able, for example, to remain in entangled states with other qubits – something that is crucial for many quantum-information schemes.
However, the quantum state of a photon will be gradually changed (or degraded) due to scattering as it travels hundreds of kilometres in a medium such as air or an optical fibre. As a result, researchers are keen on developing quantum repeaters, which take in the degraded signal, store it briefly, and then re-emit a fresh signal. This way, says Ian Walmsley of the University of Oxford, “you can build up entanglement over much longer distances”.
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