Quantum Correlation Between Distant Diamonds

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Science  02 Dec 2011:
Vol. 334, Issue 6060, pp. 1213-1214
DOI: 10.1126/science.1215444

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Entanglement is a kind of quantum correlation that distinguishes the outcomes of events in the quantum world from those in the classical one. In the classical world, chance outcomes have no strange correlations—the events at one roulette wheel in a casino have no effect on events at the other tables. In a quantum casino, we could imagine that roulette wheels are entangled, so that if one ball dropped on a black number, the ball at the next table must drop on red. The correlation of experimental outcomes created by entanglement is an essential resource for implementation of quantum information processing. Entanglement is often associated with the microscopic world; it is typically fragile and hard to preserve for large systems at macroscopic distances because of decoherence—the consequence from the inevitable coupling between macroscopic objects and their environments. Recent advances in quantum control techniques have allowed entanglement to be observed for physical systems with increasing complexity and separation distance. On page 1253 of this issue, Lee et al. (1) take an important step in this direction by demonstrating entanglement between oscillation patterns of atoms—phonon modes—of two diamond samples of millimeter size at room temperature, separated by a macroscopic distance of about 15 cm.