Universal time scalings of sensitivity in Markovian quantum metrology

Assuming a Markovian time evolution of a quantum sensing system, we provide a general characterization of the optimal sensitivity scalings with time, under the most general quantum control protocols. We allow the estimated parameter to influence both the Hamiltonian as well as the dissipative part of the quantum master equation. We focus on the asymptotic-time as well as the short-time sensitivity scalings, and investigate the relevant time scales on which the transition between the two regimes appears. This allows us to characterize, via simple algebraic conditions (in terms of the Hamiltonian, the jump operators as well as their parameter derivatives), the four classes of metrological models that represent: quadratic-linear, quadratic-quadratic, linear-linear and linear-quadratic time scalings. We also provide universal numerical methods to obtain quantitative bounds on sensitivity that are the tightest that exist in the literature.
Comment: 5+3 pages, 3 figures