Qubit metrology and decoherence

TL;DR

This paper explores how decoherence impacts the precision of quantum measurements using qubits, optimizing entanglement strategies under fixed resource constraints to improve measurement accuracy.

Contribution

It analyzes the effects of decoherence on qubit-based quantum metrology and determines optimal entanglement use given fixed qubit generation rate and measurement duration.

Findings

Decoherence limits the advantage of entanglement in quantum metrology.

Optimal entanglement strategies depend on qubit generation rate and measurement time.

Measurement uncertainty can be minimized by adjusting entanglement under resource constraints.

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 $\tau$.