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

Journal Article · · Quantum Science and Technology
 [1];  [2];  [1]
  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)
+ Show Author Affiliations
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 be useful for deriving feedback protocols and determining their optimality properties in many other quantum systems subject to measurement and unitary operations.
Research Organization:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Grant/Contract Number:
AC02-05CH11231
OSTI ID:
1575229
Journal Information:
Quantum Science and Technology, Journal Name: Quantum Science and Technology Journal Issue: 4 Vol. 2; ISSN 2058-9565
Publisher:
IOPscienceCopyright Statement
Country of Publication:
United States
Language:
English

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Cited By (3)

Manipulation of Multi‐Level Quantum Systems via Unsharp Measurements and Feedback Operations journal September 2019
Error correction of quantum system dynamics via measurement–feedback control journal July 2019
Generation and stabilization of Bell states via repeated projective measurements on a driven ancilla qubit journal May 2018

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