Atomic Gas Is a Nearly Perfect Photon Counter

Although proposed linear quantum computation schemes show promise, they are premised on photon counters with efficiencies greater than 99 percent -- beyond the reach of today's best devices. Ataç Imamoglu of the University of California, Santa Barbara, however, suggests that methods of "storing" light in an ultracold atomic gas may offer a solution.

Reporting in the Oct. 14 issue of Physical Review Letters, Imamoglu theorizes that photon-counting efficiencies better than 99 percent should be attainable by mapping the quantum state of photons from a probe laser onto an optically thick, trapped atomic gas and then measuring the state-selective scattering of photons from another laser tuned to the desired transition. The technique should be compatible with cold or warm atomic gases, but the latter might display high dark counts caused by thermal effects.