Stability of quantum Markov systems via Lyapunov methods in the Heisenberg picture

Stability of quantum Markov systems is investigated in terms of stability of invariant states. Evolutions of a quantum system in the Heisenberg picture are considered which are modeled in terms of a quantum stochastic differential equation. Using a Markov operator semigroup associated with this quantum stochastic differential equation, we derive sufficient conditions for the existence and stability of a unique and faithful invariant quantum state. The conditions are formulated in terms of algebraic constraints suitable for engineering quantum systems to be used in coherent feedback networks. To derive these conditions, we use quantum analogues of the stochastic Lyapunov stability theory.