The quantum computers of tomorrow might use photons to move data according to NIST (National Institute of Standards and Technology). The new NIST papers address one of the many challenges to a practical quantum computer: the need for a device that produces photons in ready quantities, but only one at a time, and only when the computer's processor is ready to receive them. The first paper addresses the need to be certain that a photon is indeed coming when the processor is expecting it, and that none show up unexpected. Many kinds of single-photon sources create a pair of photons and send one of them to a detector, which tips off the processor to the fact that the second, information-bearing photon is on its way. The second paper describes a photon source to address two other requirements. Quantum computers will need many such sources working in parallel, so sources must be able to be built in large numbers and operate reliably; and so that the computer can tell the photons apart, the sources must create multiple individual photons, but all at different wavelengths. “Ordinarily a particular material can produce only pairs in a specific pair of wavelengths, but our design allows production of photons at a number of regular and distinct wavelengths simultaneously, all from one source. Because the design is compatible with microfabrication techniques, this accomplishment is the first step in the process of creating sources that are part of integrated circuits, not just prototype computers that work in the hothouse of the lab,” said Alan Migdall of NIST's Optical Technology Division.