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Quantum Entanglement And Information

Quantum entanglement is a physical resource, like energy, associated with the peculiar nonclassical correlations that are possible between separated quantum systems. Entanglement can be measured, transformed, and purified. A pair of quantum systems in an entangled state can be used as a quantum information channel to perform computational and cryptographic tasks that are impossible for classical systems. The general study of the information-processing capabilities of quantum systems is the subject of quantum information.

    * 1. Quantum Entanglement
    * 2. Exploiting Entanglement: Quantum Teleportation
    * 3. Quantum Information
    * 4. Quantum Cryptography
    * 5. Quantum Computation
    * 6. Interpretative Remarks
    * Bibliography
    * Other Internet Resources
    * Related Entries

1. Quantum Entanglement
In 1935 and 1936, Schrödinger published a two-part article in the Proceedings of the Cambridge Philosophical Society in which he discussed and extended a remarkable argument by Einstein, Podolsky, and Rosen. The Einstein-Podolsky-Rosen (EPR) argument was, in many ways, the culmination of Einstein's critique of the orthodox Copenhagen interpretation of quantum mechanics, and was designed to show that the theory is incomplete. (See the entries on the EPR argument and on the Copenhagen interpretation.) In classical mechanics the state of a system is essentially a list of the system's properties — more precisely, it is the specification of a set of parameters from which the list of properties can be reconstructed: the positions and momenta of all the particles comprising the system (or similar parameters in the case of fields). The dynamics of the theory specifies how properties change in terms of a law of evolution for the state. Pauli characterized this mode of description of physical systems as a ‘detached observer' idealization. See Pauli's letter to Born in The Born-Einstein Letters (Born, 1992; p. 218). On the Copenhagen...