Researchers have managed to 'pluck' a single photon, one particle of light, out of a pulse of light. 

The researchers set out to demonstrate a scheme for pulling just one photon out of a stream, on demand. Their mechanism relies on a physical effect that they call single-photon Raman interaction, or SPRINT, which is based on a single atom, or atom-like system. 

"The advantage of SPRINT," says Dr. Barak Dayan, head of the Weizmann Institute Quantum Optics group, "is that it is completely passive -- it does not require any control fields, just the interaction between the atom and the optical pulse." In previous research, he and his team had employed SPRINT as a switch for single photons that sent them down different pathways, effectively turning the apparatus into a photonic router. In this work, the atom becomes a tap rather than a switch, snatching one photon from the flow and then turning itself off. "It is not trivial," says Dayan, "to have a mechanism that continues to function even in high fluxes of photons and to remove just one photon." 


Capturing a single photon from a pulse of light: Devices based on the Weizmann Institute model may be the backbone of future quantum communications systems. Credit: Weizmann Institute of Science

The experimental setup relies on laser cooling and trapping of atoms (in this case rubidium), the fabrication of chip-based, ultrahigh-quality glass microspheres, and optical nanofibers. 

"The ability to divert a single photon from a flow could be harnessed for various tasks," says Dayan, "from creating nonclassical states of light that are useful for basic scientific research, through eavesdropping on imperfect quantum-cryptography systems that rely on single photons, to increasing the security of your own quantum-communication systems.

The existence of photons was first suggested by Einstein in 1905, yet many of their properties are just now coming to light. Dayan believes their new method will expand our capabilities to study and control them as individual particles.

 Published in Nature Photonics.