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arXiv:quant-ph/0412149 · Physical Review A

Quantum nondemolition measurements for quantum information

Timothy C. Ralph, Stephen D. Bartlett, Jeremy L. O’Brien, Geoff J. Pryde, Howard M. Wiseman

Published Jan 31, 2006• 92 citations
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Abstract

We discuss the characterization and properties of quantum nondemolition (QND) measurements on qubit systems. We introduce figures of merit which can be applied to systems of any Hilbert space dimension, thus providing universal criteria for characterizing QND measurements. The controlled-NOT gate and an optical implementation are examined as examples of QND devices for qubits. We also consider the QND measurement of weak values.

DOI
10.1103/physreva.73.012113

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We present a review of the criteria developped to characterize the efficiency of quantum non-demolition measurement devices for travelling electromagnetic waves. These criteria describe respectively the quality of the measurement, the non-destruction of the signal, and the quantum correlations between the meter read-out and the signal output. Quantitative limits can be defined with respect to these criteria, delimiting classicad and quantum domains of operation. Moreover, some questions related to the gain on the signal channel, and to repeated QND measurements, will be also discussed.
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