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arXiv · 0705.1002

Qubit metrology and decoherence

Anil Shaji·Carlton M. Caves
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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 "cat 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 $\tau$ 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 $\tau$.

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Anil Shaji, Carlton M. Caves. 2007-05-07. Qubit metrology and decoherence. https://doi.org/10.1103/physreva.76.032111

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