A Single-Photon Source Bright Enough to Read on an Ordinary Power Meter

A single-photon source built by Sparrow Quantum and Ruhr-Universität Bochum reaches a flux of more than 500 MHz in an optical fiber, or over 500 million photons a second, the group reported in a preprint posted Sept. 4.

Photonic quantum computers and optical quantum networks are fed by single photons sent one at a time through fiber, and the authors state their motivation plainly: advanced optical quantum technologies need high-quality quantum light at very high rates. Their device is deterministic, meaning it emits a photon on demand rather than at random.

The same stream carries more than 100 pW of optical power, enough to be read with an off-the-shelf power meter, an instrument that measures light as power rather than counting individual photons. That, the authors report, gives a simple and direct way to determine how much of the source's light reaches the fiber.

Sparrow Quantum, a Copenhagen company that sells single-photon sources, announced the work on Sept. 7 and described the flux as the highest reported to date. The company also says the source is pulsed a billion times a second and that more than 50% of the light it makes reaches the fiber. Both figures are its own account of its own product, and the preprint has not been through peer review.

The authors are based at Sparrow Quantum in Frederiksberg, Denmark, and at Ruhr-Universität Bochum in Germany.