QUANTUM ENTANGLEMENT

Quantum Entanglement Between Remote Ensembles of Atoms Achieved

Reporting in the December 8 issue of the journal Nature, California Institute of Technology physicist H. Jeff Kimble and his colleagues announce the first realization of entanglement for one "spin excitation" stored jointly between two samples of atoms. In the Caltech experiment, the atomic ensembles are located in a pair of apparatuses 2.8 meters apart, with each ensemble composed of about 100,000 individual atoms.
According to Kimble, who is the Valentine Professor and professor of physics at Caltech, this research significantly extends laboratory capabilities for entanglement generation, with now-entangled "quantum bits" of matter stored with separation several thousand times greater than was heretofore possible.

[In the Caltech experiment, the entanglement involves "collective atomic spin excitations." To generate such excitations, an ensemble of cold atoms initially all in level "a" of two possible ground levels is addressed with a suitable "writing" laser pulse. For weak excitation with the write laser, one atom in the sample is sometimes transferred to ground level "b," thereby emitting a photon.]