Reconstrução de estados de sistemas quanticos compostos e caracterização de emaranhamento por operações locais e comunicação classica / State reconstruction of composite quantum systems and entanglement characterization by local operations and classical communication

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

We propose a method to obtain properties of composite quantum systems using strictly local measurements and classical communication only. This differs from schemes usually employed in quantum information protocols where global and/or joint local operations are commonly used. Our treatment consists of analysing the effect of measurements of a system over submatrices of the density matrix of the compound system. We analyse then how copies of a subsystem can be expressed in terms of these submatrices, obtaining thus the effect of the measurements done in a subsystem upon the others. We apply this result - valid for discrete Hilbert spaces of arbitrary dimension - to two central problems in quantum information protocols: the state reconstruction of composite systems and entanglement characterization. For the reconstruction task, we show how to determine a state of a arbitrary finite dimension composite system using local measurements and one-way classical communnication only. The advantage of our proposal lies in elimnating the need for joint measurements, which translates as eliminating coincidence measurements in linear optics context. We analyse entanglement characterization considering special classes of states. For high symmetry states -isotropic states, Werner states and rotationally symmetric states composed of a qubit and a qudit - we show a relation between entanglement degree and population difference measured by one subsystem conditioned to parity measurements of the other subsystem, this relation already present in gaussian symmetric states. Moreover, we propose a new family os states whose entanglement can be characterized with much fewer resources than that used for reconstruction, this resources being strictly local

ASSUNTO(S)

reconstrução de estados quanticos quantum state reconstruction quantum information theory teoria quantica de informação quantum entanglement emaranhamento quantico

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