Quantum control of a single qubit

Branczyk, Agata M., Mendonca, Paulo E. M. F., Gilchrist, Alexei, Doherty, Andrew C. and Bartlett, Stephen D. (2007) Quantum control of a single qubit. Physical Review A, 75 1: 01239-1-01239-11. doi:10.1103/PhysRevA.75.012329

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Author Branczyk, Agata M.
Mendonca, Paulo E. M. F.
Gilchrist, Alexei
Doherty, Andrew C.
Bartlett, Stephen D.
Title Quantum control of a single qubit
Journal name Physical Review A   Check publisher's open access policy
ISSN 1050-2947
Publication date 2007-01-24
Year available 2007
Sub-type Article (original research)
DOI 10.1103/PhysRevA.75.012329
Open Access Status File (Publisher version)
Volume 75
Issue 1
Start page 01239-1
End page 01239-11
Total pages 11
Place of publication College Park, MD, United States
Publisher American Physical Society
Collection year 2008
Language eng
Abstract Measurements in quantum mechanics cannot perfectly distinguish all states and necessarily disturb the measured system. We present and analyze a proposal to demonstrate fundamental limits on quantum control of a single qubit arising from these properties of quantum measurements. We consider a qubit prepared in one of two nonorthogonal states and subsequently subjected to dephasing noise. The task is to use measurement and feedback control to attempt to correct the state of the qubit. We demonstrate that projective measurements are not optimal for this task, and that there exists a nonprojective measurement with an optimum measurement strength which achieves the best trade-off between gaining information about the system and disturbing it through measurement backaction. We study the performance of a quantum control scheme that makes use of this weak measurement followed by feedback control, and demonstrate that it realizes the optimal recovery from noise for this system. We contrast this approach with various classically inspired control schemes.
Keyword Optics
Q-Index Code C1
Q-Index Status Confirmed Code

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Created: Wed, 09 Apr 2008, 13:51:38 EST by Jenny Robinson on behalf of School of Mathematics & Physics