Closer to a Quantum Internet

A demonstration of photon-pair generation from visible to telecom wavelengths may speed the development of quantum networks.

t has been nearly two decades since quantum computation first captured the imagination of the general public as a potential way to break the toughest cryptographic codes. Now, quantum information systems are becoming a reality, not for code breaking but as code generators whose security is governed by the laws of physics rather than computational complexity. This gives quantum communication systems an advantage over classical systems whose codes could, in principle, always be broken by some clever algorithm or a quantum computer. Yet there is still a key stumbling block to the construction of the quantum internet: transmitting quantum information over long distances. In a paper in Physical Review Letters, Julia Fekete at the Institute of Photonic Sciences, Spain, and colleagues report the first demonstration of a spectrally narrow-band source of photon pairs where one photon can address solid-state quantum memories at visible wavelengths, and the other is at a wavelength where telecommunications systems operate [1]. This is a critical element of a telecom-compatible quantum repeater and therefore brings us one step closer to the realization of a quantum internet.