Title: What is the optimal way to prepare a Bell state using measurement and feedback?

Abstract

Recent work has shown that the use of quantum feedback can significantly enhance both the speed and success rate of measurement-based remote entanglement generation, but it is generally unknown what feedback protocols are optimal for these tasks. In this work, we consider two common measurements that are capable of projecting into pairwise entangled states, namely half- and full-parity measurements of two qubits, and determine in each case a globally optimal protocol for generation of entanglement. For the half-parity measurement, we rederive a previously described protocol using more general methods and prove that it is globally optimal for several figures of merit, including maximal concurrence or fidelity and minimal time to reach a specified concurrence or fidelity. For the full-parity measurement, we derive a protocol for rapid entanglement generation related to that of (Hill, Ralph, Phys. Rev. A 77, 014305), and then map the dynamics of the concurrence of the state to the Bloch vector length of an effective qubit. This mapping allows us to prove several optimality results for feedback protocols with full-parity measurements. We further show that our full-parity protocol transfers entanglement optimally from one qubit to the other amongst all measurement-based schemes. The methods developed here will bemore » useful for deriving feedback protocols and determining their optimality properties in many other quantum systems subject to measurement and unitary operations.« less

Authors:

Martin, Leigh  ^[1];

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Sayrafi, Mahrud ^[2]; Whaley, K. Birgitta ^[1]

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1. Berkeley Center for Quantum Information and Computation, CA (United States); Univ. of California, Berkeley, CA (United States)
2. Berkeley Center for Quantum Information and Computation, CA (United States)

Publication Date:

2017-08-22

Research Org.:

Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)

OSTI Identifier:

1575229

Grant/Contract Number:  

AC02-05CH11231

Resource Type:

Accepted Manuscript

Journal Name:

Quantum Science and Technology

Additional Journal Information:

Journal Volume: 2; Journal Issue: 4; Journal ID: ISSN 2058-9565

Publisher:

IOPscience

Country of Publication:

United States

Language:

English

Subject:

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS