The extraordinary promise of quantum information processing—solving problems that classical computers can't, perfectly secure communication—depends on a phenomenon called "entanglement," in which the physical states of different quantum particles become interrelated. But entanglement is very fragile, and the difficulty of preserving it is a major obstacle to developing practical quantum information systems.
In a series of papers since 2008, members of the Optical and Quantum Communications Group at MIT's Research Laboratory of Electronics have argued that optical systems that use entangled light can outperform classical optical systems—even when the entanglement breaks down.
Two years ago, they showed that systems that begin with entangled light could offer much more efficient means of securing optical communications. And now, in a paper appearing in Physical Review Letters, they demonstrate that entanglement can also improve the performance of optical sensors, even when it doesn't survive light's interaction with the environment.
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