Monday, May 31, 2010

Decoherence - Greg Egan

"The basic idea is this: a quantum system, A, in isolation, behaves in a characteristically quantum-mechanical fashion, exhibiting interference effects that reflect the phase difference between the various components of its state vector. For example, if A consists of an electron in a state that is a superposition of equal parts spin up and spin down, there will be measurements that can be performed on the electron that will be sensitive to the phase relationship between these two components. This is quite different from the classical notion of probability: there isn't merely a 50% chance for the electron's spin to be up or down; rather, both possibilities exist simultaneously, and the phase describes a relationship between them that would be meaningless if either was absent."

4 out of 5

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