Physicists at the Max Planck Institute for Quantum Optics in Garching, Germany, have used a rubidium atom that was strongly coupled to a high-finesse optical cavity (above) to produce, on demand, a sequence of single photons with well-defined and identical properties. The photons are created by an adiabatically driven stimulated Raman transition between two atomic ground states. This process is performed in a unitary way and is therefore reversible, which the researchers say makes it ideal for sending and receiving single photon states within a quantum-computing network. The group described the process in the Aug. 5 issue of Physical Review Letters.