Coherence and nonlocality

Usually quantum nonlocality is discussed in terms of correlated multiparticle systems such as those discussed by John Bell in his famous 1964 theorem and then later clarified by GHZ, David Mermin and others.

But more striking and significant is the qualitative nonlocal phenomena associated with coherent states, for example in Bose-Einstein condensation, superfluidity, Frohlich coherence, and perhaps other phenomena up to cosmological scales...

In fact, theoretically these two kinds of nonlocality have precisely the same basis: the unmeasured singlet state uncovered by EPR is a coherent 'pure state' despite its spacial extension, and when the parts are realized in a measurement (a la Bell) this coherence is harvested or cashed in.

Whereas the "EPR" connections are ephemeral and fragile, some forms of nonlocal coherence are robust.

Explorations | Nonlocality | Coherence