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In a key step toward quantum computing and communication, two groups have used clusters of atoms to catch and release single photons, and a third has managed to entangle two such clusters. Many quantum-information schemes depend on transmitting quantum bits, or qubits, as photon states. Qubits sent down optical fibers would require periodic purification, which means storing and releasing photons. Teams from Harvard University and the Georgia Institute of Technology independently accomplished this feat. They generated single photons from a coherent quantum ensemble of rubidium atoms and sent them into a second ensemble, which could be rendered opaque by a laser pulse to catch or store the photon and transparent by another pulse to release it, all without degrading the photon's quantum abilities. The third team, led by California Institute of Technology researchers, entangled two ensembles—creating a quantum link between them—across a room. Such entanglement is another requirement for propagating a signal. Check the December 8, 2005, Nature for details.
