Atomic blockade: Technique efficiently creates single photons for quantum information processing

Using lasers to excite just one atom from a cloud of ultra-cold rubidium gas, physicists have developed a new way to rapidly and efficiently create single photons for potential use in optical quantum information processing -- and in the study of dynamics and disorder in certain physical systems.

The technique takes advantage of the unique properties of atoms that have one or more electrons excited to a condition of near-ionization known as the Rydberg state. Atoms in this highly excited state -- with a principal quantum number greater than 70 -- have exaggerated electromagnetic properties and interact strongly with one another. That allows one Rydberg atom to block the formation of additional excited atoms within an area of 10 to 20 microns.

That single Rydberg atom can then be converted to a photon, ensuring that -- on average -- only one photon is produced from a rubidium cloud containing hundreds of densely-packed atoms. Reliably producing a single photon with well known properties is important to a several research areas, including quantum information systems.