Phys. Rev. A 65, 012317 (2001) [4 pages]Impossibility criterion for obtaining pure entangled states from mixed states by purifying protocolsReceived 9 July 2001; published 13 December 2001 Purifying noisy entanglement is a protocol that can increase the entanglement of a mixed state (as a source) at the expense of the entanglement of others (such as an ancilla) by collective measurement. A protocol with which one can get a pure entangled state from a mixed state is defined as purifying mixed states. We address a basic question: can one get a pure entangled state from a mixed state? We give a necessary and sufficient condition of purifying a mixed state by fit local operations and classical communication and show that for a class of source states and ancilla states in arbitrary bipartite systems purifying mixed states is impossible by finite rounds of purifying protocols. For 2⊗2 systems, it is proved that arbitrary states cannot be purified by individual measurement. The possible application and meaning of the conclusion are discussed. © 2001 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevA.65.012317
DOI:
10.1103/PhysRevA.65.012317
PACS:
03.67.-a, 03.65.Ud
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