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

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Author(s)
Combes, Joshua
Wiseman, Howard M
Jacobs, Kurt
O'Connor, Anthony J
Griffith University Author(s)
Year published
2010
Metadata
Show full item recordAbstract
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 ...
View more >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.
View less >
View more >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.
View less >
Journal Title
Physical Review A
Volume
82
Issue
2
Copyright Statement
© 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.
Subject
Mathematical sciences
Physical sciences
Quantum information, computation and communication
Chemical sciences