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Research in Optical Sciences

Quantum discord required for modifying the overlap states

Luis Roa

Published Jan 1, 2014• 0 citations
Publisher

Abstract

In the schemes for decreasing probabilistically and increasing deterministically the overlap between two quantum states a unitary operation is responsible for coupling two quantum systems, thus introducing correlation between them. We study the quantum correlations required to achieve the task.
DOI
10.1364/hilas.2014.jw2a.57

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The processes for decreasing probabilistically and increasing deterministically the overlap between two quantum states must be assisted by an auxiliary quantum system. The probabilistic scheme is implemented through a unitary-reduction process, while the deterministic one is accomplished only with a joint unitary transformation. In both schemes a unitary operation is responsible for coupling the two involved systems thus introducing correlation between them. In this work we study the quantum correlations required to achieve the probabilistic scheme with optimal probability, and we characterize the quantum correlation involved in the deterministic procedure. We find a that both schemes can be accomplished with quantum discord and without entanglement. In addition, we propose a physical implementation of the probabilistic scheme with twin photons generated in the process of spontaneous parametric down-conversion. The states are encoded in the polarization of a single photon and the auxiliary system becomes its propagation path; the second photon is used for heralded detection.
The task of changing the overlap between two quantum states cannot be performed by making use of unitary evolution only. However, by means of a unitary-reduction process, it could be modified. Here we study in detail the problem of mapping two known pure states onto two other states in such a way that the overlap between the outcome states is different from the one of the initial states. We show that the modulus of the overlap can be reduced only probabilistically, whereas it can be increased deterministically. Our analysis shows that the phases of the involved overlaps play an important role in the increase of the success probability of the desired process.
The task of changing the overlap between two quantum states can not be performed by making use of a unitary evolution only. However, by means of a unitary-reduction process it can be probabilistically modified. Here we study in detail the problem of mapping two known pure states onto other two states in such a way that the final inner product between the outcome states is different from the inner product of the initial states. In this way we design an optimal non-orthogonal quantum state preparation scheme by starting from an orthonormal basis. In this scheme the absolute value of the inner product can be reduced only probabilistically whereas it can be increased deterministically. Our analysis shows that the phases of the involved inner products play an important role in the increase of the success probability of the desired process.