Quantum entanglement is the mechanism by which quantum correlations between two sub-systems survive even after being physically separated from an interaction region. The correlations could in principle survive without neither time nor space constraint.
Quantum entanglement was originally conceived of as a critique of quantum mechanics by Einstein and some colleagues in the EPR thought experiment, but the effect was later proved to be real.
It is the basis for applied research, particularly in the area of quantum computing and quantum information, where it enables two bits of information to be stored in a single qubit (or quantum bit).
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