Non-Locality

Non-locality is one of the central phenomena of quantum mechanics. It determines how well two distant parties (or indeed physical systems) can coordinate their actions without exchanging information. By virtue of being non-local, quantum mechanics allows for much more effective forms of coordination than would be possible in a classical world. This improvement is made possible by the more well-known phenomenon of quantum entanglement.

The first important consequence of quantum non-locality is that it allows researchers to verify experimentally that the world is indeed not classical. This is done by testing how well two remote parties can coordinate their actions. The amount of coordination is measured with respect to Bell inequalities or in so-called non-local games. Many such tests have been performed and these show (up to experimental errors) that more effective forms of coordination than could exist classically really are possible.

But non-locality and quantum entanglement are not merely of conceptual interest. Their existence has practical consequences, enabling much stronger forms of information processing, communication and cryptography. Examples include quantum teleportation and quantum key exchange.

The study of non-locality encompasses questions such as: What are the limits of quantum non-locality? How can we find these limits efficiently? Can we explain these physical limits? And, how can we best exploit non-locality to solve information processing problems?

CQT is a forerunner in non-locality research, with CQT researchers' contributions including the recent discovery of the relation between the uncertainty principle and non-locality (Science 330, no 7006, 1072-1074, 2010), the principle of information causality (Nature 461, 1101-1104, 2009), and the latest experimental tests of the Leggett inequality (Nature Physics, 4, 681-685, 2008).

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