A method for solving exact-controllability problems governed by closed quantum spin systems

The Liouville-von Neumann master equation models closed quantum spin systems that arise in Nuclear Magnetic Resonance applications. In this paper, an efficient and robust computational framework to solve exact-controllability problems governed by the Liouville-von Neumann master equation, that models control quantum spin systems, is presented. The proposed control framework is based on a new optimization-based formulation of exact-controllability quantum spin problems that allows the application of efficient computational techniques. This formulation results in an optimality system with four differential equations and an optimality condition. The differential equations are approximated with an appropriate modified Crank-Nicholson scheme and the resulting discretized optimality system is solved with a matrix-free Krylov-Newton scheme combined with a cascadic NCG initialization. Results of numerical experiments demonstrate the ability of the proposed framework to solve quantum spin exactcontrollability control problems.