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It is now widely believed that in the near future quantum sensing devices will be realized to outperform some of our current sensing devices. As quantum metrology protocols are comprised of three stages: probe state preparation, sensing followed by readout, it is important that the time for all three steps are accounted when the performance is determined. Historically the time required for the first and last stages has usually been neglected, which could be unrealistic when entangled resources are used.
Entangled resources lose their sensitivity in time under noise, and hence the sensing time with these resources is limited. To avoid this degradation of sensitivity, we could repeat the protocol to refresh the entanglement in the resources. However, as the process of the preparation and the readout of the entangled probe state costs us a certain period of time, we need to optimize the sensing protocol throughout the three stages. We find that an entangled state probe can give an advantage over separable ones only if the entangled state preparation and readout times are lower than a certain threshold and illustrate this result in an optical setting.
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