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arXiv:0707.3001 · Quantum Information Processing

Optimality of Feedback Control Strategies for Qubit Purification

Howard M. Wiseman, Luc Bouten

Published Apr 4, 2008• 41 citations
arXivHTMLPDF
DOI
10.1007/s11128-008-0075-8

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In classical control theory, tracking refers to the ability to perform measurements and feedback on a classical system in order to enforce some desired dynamics. In this paper we investigate a simple version of quantum tracking, namely, we look at how to optimally transform the state of a single qubit into a given target state, when the system can be prepared in two different ways, and the target state depends on the choice of preparation. We propose a tracking strategy that is proved to be optimal for any input and target states. Applications in the context of state discrimination, state purification, state stabilization, and state-dependent quantum cloning are presented, where existing optimality results are recovered and extended.