Max Planck researchers develop single-photon server

March 20, 2007, Garching, Germany--Physicists at the Max Planck Institute of Quantum Optics have succeeded in turning a Rubidium atom into a single-photon server. The research appears in Nature Physics 569, "A Single-Photon Server with Just One Atom," published online March 11, 2007.

In 2005 a team of physicists in the group of Professor Gerhard Rempe at the Max Planck Institute of Quantum Optics in Garching near Munich, Germany was able to increase the trapping times of single atoms in a cavity significantly by using three-dimensional cavity cooling. In the present article they report on results where they have been able to combine this cavity cooling with the generation of single photons in a way that a single atom can generate up to 300,000 photons, one at a time.

The experiment uses a magneto-optical trap to prepare ultracold Rubidium atoms inside a vacuum chamber. These atoms are then trapped inside the cavity in the dipole potential of a focused laser beam. By applying a sequence of laser pulses from the side, a stream of single photons is emitted from the cavity. Between each emission of a single photon the atom is cooled, preventing it from leaving the trap.

Compared with other methods of single-photon generation the photons are of a very high quality; that is, their energy varies very little, and the properties of the photons can be controlled. They can for instance be made indistinguishable, a property necessary for quantum computation.

Quantum information processing with photons has therefore moved one step closer. With the single-photon server operating, Gerhard Rempe and his team are now ready to take on the next challenges such as deterministic atom-photon and atom-atom entanglement experiments.

For more information, visit http://www.mpq.mpg.de.