Ancilla-assisted sequential approximation of nonlocal unitary operations

Journal Article · Thu Sep 15 04:00:00 EDT 2011 · Physical Review. A

DOI:https://doi.org/10.1103/PHYSREVA.84.032323· OSTI ID:22068668

Saberi, Hamed ^[1]

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1. Institute for Theoretical Physics, University of Regensburg, D-93040 Regensburg (Germany)

We consider the recently proposed (no-go) theorem of Lamata et al.[Phys. Rev. Lett. 101, 180506 (2008)] on the impossibility of sequential implementation of global unitary operations with the aid of an itinerant ancillary system and view the claim within the language of Kraus representation. By virtue of an extremely useful tool for analyzing entanglement properties of quantum operations, namely, operator-Schmidt decomposition, we provide alternative proof to the no-go theorem and also study the role of initial correlations between the qubits and ancilla in sequential preparation of unitary entanglers. Despite the negative response from the no-go theorem, we demonstrate explicitly how the matrix-product operator (MPO) formalism provides a flexible structure to develop protocols for sequential implementation of such entanglers with an optimal fidelity. The proposed numerical technique, which we call variational matrix-product operator (VMPO), offers a computationally efficient tool for characterizing the ''globalness'' and entangling capabilities of nonlocal unitary operations.

• OSTI ID: 22068668
• Journal Information: Physical Review. A, Journal Name: Physical Review. A Journal Issue: 3 Vol. 84; ISSN 1050-2947; ISSN PLRAAN
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
74 ATOMIC AND MOLECULAR PHYSICS
APPROXIMATIONS
CORRELATIONS
IMPLEMENTATION
MATRICES
QUANTUM ENTANGLEMENT
QUBITS
VARIATIONAL METHODS