A photon gun capable of reliably producing single photons of different colors has been developed by researchers at the Max Planck Institute for the Science of Light in Erlangen, Germany. It could become an important building block of a quantum Internet, Technology Review Physics arXiv blog reports.

They built a kind of photon supergun: a disc-shaped crystal of lithium niobate zapped with 582nm light from a neodymium-doped yttrium aluminium garnet (Nd:YAG) laser.

Lithium niobate is a nonlinear material that causes single photons to spontaneously convert into photon pairs. That’s significant because the detection of one photon is an unambiguous sign that another has also been emitted. It’s like a time stamp that says a photon is on its way, so there can be no confusion over whether the gun is secretly leaking information to a potential eavesdropper.

The gun is also fast, emitting some 10 million pairs of photons per second per mW, and also two orders of magnitude more efficient than other photon guns. The gun can also be tuned to various different atomic transitions, allowing physicists and engineers to play with a variety of different atoms for quantum information storage.

Ref.: Michael Förtsch et al., A Versatile Source of Single Photons for Quantum Information Processing, arxiv.org/abs/1204.3056: