2017/04/02 by Leigh S. Martin, Mahrud Sayrafi, Martin, Leigh S. +3 · 1 citation
Computer Science · Physics and Astronomy · #FOS: Physical sciences #Quantum Computing Algorithms and Architecture #Quantum Information and Cryptography #Quantum Mechanics and Applications #Quantum Physics (quant-ph)
paper · pdf · doi:10.48550/arxiv.1704.00332
openalex publication_date 2017/04/02 · openalex created_date 2022/10/05 · openalex updated_date 2026/07/28
Recent work has shown that use of quantum feedback can significantly enhance\nboth the speed and success rate of measurement-based remote entanglement\ngeneration, but it is generally unknown what feedback protocols are optimal for\nthese tasks. Here we consider two common measurements that are capable of\nprojecting into pairwise entangled states, namely half- and full-parity\nmeasurements of two qubits, and determine in each case a globally optimal\nprotocol for generation of entanglement. For the half-parity measurement, we\nrederive a previously described protocol using more general methods and prove\nthat it is globally optimal for several figures of merit, including maximal\nconcurrence or fidelity, and minimal time to reach a specified concurrence or\nfidelity. For the full-parity measurement, we derive a protocol for rapid\nentanglement generation related to that of (C. Hill, J. Ralph, Phys. Rev. A 77,\n014305 (2008)), and then map the dynamics of the concurrence of the state to\nthe Bloch vector length of an effective qubit. This mapping allows us to prove\nseveral optimality results for feedback protocols with full-parity\nmeasurements. We further show that our full-parity protocol transfers\nentanglement optimally from one qubit to the other amongst all\nmeasurement-based schemes. The methods developed here will be useful for\nderiving feedback protocols and determining their optimality properties in many\nother quantum systems subject to measurement and unitary operations.\n