Identification of time-varying signals in quantum systems

The identification of time-varying parameters (e.g., directly inaccessible in situ signals vacuum and low-temperature environments) is prevalent for characterizing the dynamics quantum processes. Under certain circumstances, they can be identified from time-resolved measurements via Ramsey interferometry experiments, but only with specially designed probe systems explicitly read out, a rigorous identifiability analysis lacking, i.e., whether measurement data are sufficient unambiguous identification. In this paper we formulate problem as invertibility input-output mapping associated system which an algebraic criterion derived based on system's relative degree. also leads to inversion-based algorithm numerically identifying parameters, computationally much more efficient than nonlinear regression methods. effectiveness demonstrated by numerical examples.