Enhancement of quantum sensing by noncanonical effects

Equilibrium probes have been widely used in various schemes of sensing to quantum reservoirs. Many previous studies assumed that the probe-reservoir coupling is sufficiently weak such that the equilibrium state of the probe is approximately described by a canonical Gibbs state at the same temperature of the reservoir. Such a weak-coupling approximation severely restricts the range of application for an equilibrium-probe-based quantum sensing scenario. Going beyond the weak-coupling limitation, we here investigate the noncanonical effect, which is naturally induced by strong couplings, on the performance of a quantum sensing scheme. In this scheme, a quantum two-level system is used as the probe to estimate the parameters of a dissipative bosonic reservoir, by employing the polaron transformation approach. It is found that, compared with that of the canonical-equilibrium-state case, the noncanonical effect can effectively boost the sensing precision at both zero and finite temperatures. Paving the way toward realizing high-precision quantum sensing in practice, our result reveals the positive role of noncanonicality in the studies of quantum technologies.