Quantum metrology including state preparation and readout times

TL;DR

This paper investigates how the time costs of preparing and reading out quantum states affect the potential precision advantages of quantum sensors, especially under decoherence, revealing limitations on entanglement benefits.

Contribution

It introduces a realistic model incorporating preparation and readout times and analyzes their impact on quantum metrology advantages under decoherence.

Findings

Entangled states only outperform separable states if preparation and readout times are below a certain threshold.

Dephasing lowers the threshold, making quantum advantage harder to achieve.

Maximum entanglement provides benefits only up to a finite number of particles, which is reduced by decoherence.

Abstract

There is growing belief that the next decade will see the emergence of sensing devices based on the laws of quantum physics that outperform some of our current sensing devices. For example, in frequency estimation, using a probe prepared in an entangled state can, in principle, lead to a precision gain compared to a probe prepared in a separable state. Even in the presence of some forms of decoherence, it has been shown that the precision gain can increase with the number of probe particles $N$. Usually, however, the entangled and separable state preparation and readout times are assumed to be negligible. We find that a probe in a maximally entangled (GHZ) state can give an advantage over a separable state only if the entangled state preparation and readout times are lower than a certain threshold. When the probe system suffers dephasing, this threshold is much lower (and more difficult to attain) than it is for an isolated probe. Further, we find that in realistic situations the maximally entangled probe gives a precision advantage only up to some finite number of probe particles $N_\text{cutoff}$ that is lower for a dephasing probe than it is for an isolated probe.