Controllability characterization of linear ensemble systems

In this paper, we study the control of the class of time-invariant linear ensemble systems, whose natural dynamics vary linearly with the system parameter. This class of ensemble control systems arises from practical engineering and physical applications, such as transport of quantum atoms and steering of uncertain harmonic systems. We, in particular, consider the ensemble systems with strictly positive or negative parameter values and derive explicit necessary and sufficient controllability conditions, which are easy to be checked. Our derivation is based on the notion of polynomial approximation, where the elements of the reachable set are represented in polynomials of the system parameter and used to approximate the desired state of interest. In addition, we highlight the role of the spectra of the system matrices play in the determination of ensemble controllability. Illustrative examples with numerical simulations are provided to demonstrate the tractability of the developed controllability conditions.