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.
|Number of pages||16|
|Journal||Physical Review A - Atomic, Molecular, and Optical Physics|
|Publication status||Published - 11 Jul 2008|