Friday, June 14, 2013

1306.3151 (Rajarshi Pal et al.)

Non-locality breaking qubit channels    [PDF]

Rajarshi Pal, Sibasish Ghosh
Entanglement in states of composite quantum systems is a manifestation of non-classical behavior of the systems. Can we quantitatively relate these two aspects, namely, entanglement and non-classicality? Non-classicality is manifested in different ways, among which non-locality is of prime importance. Instead of comparing the amounts of entanglement and non-locality in a state of a composite system, we intend to compare here--in a dual picture--quantum channels which can break entanglement and those which can bring every state to a local one. In the absence of any useful necessary-sufficient condition for identifying a state to be local, we check here whether, upon the channel action, all the states satisfy any local-realistic inequality. We find that if a unital qubit channel, after acting on one of the qubits of a two-qubit maximally entangled state, brings it to a Bell-CHSH inequality non-violating state, then the channel does the similar job for all two-qubit states. Unfortunately such a feature is not universally true in the case of non-unital qubit channels, even though there are exceptions e.g., the amplitude damping channel.
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