Single light particles can be manipulated to form a mixture or 'superposition' of two colours at the same time.
Quantum computing requires particles to be simultaneously in two quantum states, but the creation of two-colour photons requires individual light particles to interact, which they rarely do. To increase the chances of such interactions occurring, Stéphane Clemmen at Cornell University in Ithaca, New York, and his colleagues encouraged a stream of single photons to combine with photons from two strong laser pumps by channelling them all through a cryogenically cooled 100-metre-long optical fibre. The lasers simultaneously bumped each photon's frequency up and down, producing particles in a superposition of two colours — something the team proved experimentally.
Such bichromatic photons could be used to encode information in quantum computers, or to connect systems in a quantum network, say the authors.