Maximally robust unravelings of quantum master equations

The stationary state of an open quantum system has infinitely many represen tations as an ensemble of pure states. We argue that the most natural ensem ble is the most robust physically realizable ensemble. Robustness is quanti fied by the survival probability. Physical realization requires monitoring the environment to "unravel" the dissipative evolution. (C) 1998 Elsevier S cience B.V.