<i>Quantum metrology in non-collective, spatiotemporally correlated quantum noise environments</i>

We study the impact of non-collectivity on frequency estimation by Ramsey interferometry in the presence of spatiotemporally correlated Gaussian quantum noise. In previous work [1], it was found that the uncontrolled buildup of spatiotemporal correlations between the probes mediated by a quantum environment leads to sub-SQL scaling in entanglement-assisted parameter estimation for the paradigmatic case of qubit probes subject to collective noise from a bosonic environment. With that in mind, we consider two types of non-collective couplings between probes and environment: the simplest digital departure from a collective model, and a limit where the position of the probes are Gaussian random variables. We find that, in both cases, non-collectivity can be regarded as a metrological resource reducing the frequency uncertainty, leading to a constant factor advantage with respect to the collective result in the first case, and to superclassical scaling in the second.

[1] Phys. Rev. A (Rapid Communications) 98, 020102 (2018).