Convergent control strategy of state in open quantum systems

A control strategy of quantum states of open quantum system based on Lyapunov method is proposed. On the basis of choosing the average of observable operators as a Lyapunov function, the control laws are designed in interaction picture. We analyze the largest invariant set of the controlled system via Barbalat´s Lemma. Based on some assumptions of Hamiltonians, we propose a sufficient condition of the observable operator to guarantee the convergence of the open quantum system, and proof that the proposed strategy can make any pure target state in decoherence-free subspace be globally asymptotic stable under the sufficient condition. Also, we provide a method to construct the observable operator via Schmidt orthogonalization. Numerical experiments on a three-level system validate the effectiveness of the proposed control strategy.