Rapid purification of quantum systems by measuring in a feedback-controlled unbiased basis

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Title Rapid purification of quantum systems by measuring in a feedback-controlled unbiased basis
Author Combes, Joshua Leo Alfred; Wiseman, Howard Mark; Jacobs, Kurt; O'Connor, Anthony John
Journal Name Physical Review A
Year Published 2010
Place of publication Physical Review A
Publisher American Physical Society
Abstract Rapid purification by feedback—specifically, reducing the mean impurity faster than by measurement alone—can be achieved by choosing the eigenbasis of the density matrix to be unbiased relative to the measurement basis. Here we further examine the protocol introduced by Combes and Jacobs [Phys. Rev. Lett. 96, 010504 (2006)] involving continuous measurement of the observable Jz for a D-dimensional system. We rigorously rederive the lower bound (2/3)(D+1) on the achievable speedup factor and also an upper bound, namely D2/2, for all feedback protocols that use measurements in unbiased bases. Finally, we extend our results to n independent measurements on a register of n qubits and derive an upper bound on the achievable speedup factor that scales linearly with n.
Peer Reviewed Yes
Published Yes
Alternative URI http://dx.doi.org/10.1103/PhysRevA.82.022307
Copyright Statement Copyright 2010 American Physical Society. This is the author-manuscript version of this paper. Reproduced in accordance with the copyright policy of the publisher. Please refer to the journal's website for access to the definitive, published version.
Volume 82
Issue Number 2
Page from 022307 -1
Page to 022307 -9
ISSN 033810
Date Accessioned 2010-09-17
Language en_AU
Research Centre Centre for Quantum Dynamics
Faculty Faculty of Science, Environment, Engineering and Technology
Subject Quantum Information, Computation and Communication
URI http://hdl.handle.net/10072/34407
Publication Type Journal Articles (Refereed Article)
Publication Type Code c1

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