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Measurement in control and discrimination of entangled pairs under self-distortion
Quantum correlations and entanglement are fundamental resources for quantum
information and quantum communication processes. Developments in these fields
normally assume these resources stable and not susceptible of distortion. That
is not always the case, Heisenberg interactions between qubits can produce
distortion on entangled pairs generated for engineering purposes (e. g. for
quantum computation or quantum cryptography). Experimental work shows how to
produce entangled spin qubits in quantum dots and electron gases, so its
identification and control are crucial for later applications. The presence of
parasite magnetic fields modifies the expected properties and behavior for
which the pair was intended. Quantum measurement and control help to
discriminate the original state in order to correct it or, just to try of
reconstruct it using some procedures which do not alter their quantum nature.
Two different kinds of quantum entangled pairs driven by a Heisenberg
Hamiltonian with an additional inhomogeneous magnetic field which becoming
self-distorted, can be reconstructed without previous discrimination by adding
an external magnetic field, with fidelity close to 1 (with respect to the
original state, but without discrimination). After, each state can be more
efficiently discriminated. The aim of this work is to show how combining both
processes, first reconstruction without discrimination and after discrimination
with adequate non-local measurements, it's possible a) improve the
discrimination, and b) reprepare faithfully the original states. The complete
process gives fidelities better than 0.9. In the meanwhile, some results about
a class of equivalence for the required measurements were found. This property
lets us select the adequate measurement in order to ease the repreparation
after of discrimination, without loss of entanglement.Comment: 6 figure
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