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State-merging
In quantum information theory, quantum state merging is the transfer of a quantum state when the receiver already has part of the state. The process optimally transfers partial information using entanglement and classical communication. It allows for sending information using an amount of entanglement given by the conditional quantum entropy, H(A, B)\,=\,H(AB)-H(B) \, . with H(A) the Von Neumann entropy, H(A):=-Tr\rho_A\log\rho_A. It thus provides an operational meaning to this quantity. Unlike its classical counterpart, the quantum conditional entropy can be negative. In this case, the sender can transfer the state to the receiver using no entanglement, and as an added bonus, this amount of entanglement can be gained, rather than used. Thus quantum information can be negative. The amount of classical information needed is the mutual information I(A:R):=H(A)+H(R)-H(AR). The case where the classical communication is replaced by quantum communication was considered in. This is k ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quantum Discord
In quantum information theory, quantum discord is a measure of nonclassical correlations between two subsystems of a quantum system. It includes correlations that are due to quantum physical effects but do not necessarily involve quantum entanglement. The notion of quantum discord was introduced by Harold Ollivier and Wojciech H. ZurekWojciech H. Zurek, ''Einselection and decoherence from an information theory perspective'', Annalen der Physik vol. 9, 855–864 (2000abstract/ref>Harold Ollivier and Wojciech H. Zurek, ''Quantum Discord: A Measure of the Quantumness of Correlations'', Physical Review Letters vol. 88, 017901 (2001abstract/ref> and, independently by Leah Henderson and Vlatko Vedral. Olliver and Zurek referred to it also as a measure of ''quantumness'' of correlations. From the work of these two research groups it follows that quantum correlations can be present in certain mixed separable states;Paolo Giorda, Matteo G. A. Paris: ''Gaussian quantum discord'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |