continuous quantum error correction via quantum feedback：量子反馈连续量子纠错.pdfVIP

PHYSICAL REVIEW A, VOLUME 65, 042301 Continuous quantum error correction via quantum feedback control Charlene Ahn,* Andrew C. Doherty,† and Andrew J. Landahl‡ Institute for Quantum Information, California Institute of Technology, Pasadena, California 91125 Received 18 October 2001; published 14 March 2002 We describe a protocol for continuously protecting unknown quantum states from decoherence that incor- porates design principles from both quantum error correction and quantum feedback control. Our protocol uses continuous measurements and Hamiltonian operations, which are weaker control tools than are typically assumed for quantum error correction. We develop a cost function appropriate for unknown quantum states and use it to optimize our state-estimate feedback. Using Monte Carlo simulations, we study our protocol for the three-qubit bit-flip code in detail and demonstrate that it can improve the fidelity of quantum states beyond what is achievable using quantum error correction when the time between quantum error-correction cycles is limited. DOI: 10.1103/PhysRevA.65.042301 PACS numbers: 03.67.Lx, 03.65.Yz, 03.65.Ta I. INTRODUCTION available controlling manipulations have bounded strengths Long-lived coherent quantum states are essential for 12. many quantum information science applications, including The availability of quantum error correction, which can quantum cryptography 1, quantum computation 2,3, and protect unknown quantum states, and quantum feedback con- quantum teleportation