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arXiv:0705.1002 · Physical Review A

Qubit metrology and decoherence

Anil Shaji, Carlton M. Caves

Published Sep 13, 2007• 127 citations
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Abstract

Quantum properties of the probes used to estimate a classical parameter can be used to attain accuracies that beat the standard quantum limit. When qubits are used to construct a quantum probe, it is known that initializing $n$ qubits in an entangled state, rather than in a separable state, can improve the measurement uncertainty by a factor of $1∕\sqrt{n}$. We investigate how the measurement uncertainty is affected when the individual qubits in a probe are subjected to decoherence. In the face of such decoherence, we regard the rate $R$ at which qubits can be generated and the total duration $\ensuremath{\tau}$ of a measurement as fixed resources, and we determine the optimal use of entanglement among the qubits and the resulting optimal measurement uncertainty as functions of $R$ and $\ensuremath{\tau}$.

DOI
10.1103/physreva.76.032111

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