Entanglement Enhanced Sensing with Qubits affected by non-Markovian Dephasing

TL;DR

This paper investigates how entanglement can enhance sensing sensitivity in Ramsey spectroscopy under non-Markovian dephasing noise, showing that correlated noise can be exploited for better scaling with entangled probes.

Contribution

It demonstrates that entangled probes can outperform separable states in Ramsey spectroscopy affected by correlated classical dephasing noise.

Findings

Entanglement improves sensitivity scaling under correlated noise.

A fundamental limit to sensitivity is derived based on the signal-to-noise ratio.

Entangled probes outperform separable states with suitable noise correlations.

Abstract

Entanglement has been proposed as a means to improve the sensitivity of sensing weak signals. While the degree of this quantum advantage is well understood in noiseless settings, the situation is more complex under realistic conditions, where the system is subject to decoherence. In this case, the enhancement depends on the specific noise characteristics. Previous treatments of colored noise typically assume that the noise is uncorrelated between successive experiments. Here, we consider the scenario in which the noise exhibits correlations across multiple shots. We derive a simple fundamental limit to the sensitivity based on the fact that the sensitivity cannot be better than the signal-to-noise ratio seen by the probe. Focusing on Ramsey spectroscopy with probes affected by pure classical dephasing, we show that, for suitable spatial and temporal noise correlations, entangled probes achieve a better scaling of the sensitivity with the number of probes than separable states. This demonstrates that entanglement can provide a substantial improvement for Ramsey spectroscopy subject to correlated noise.