Nonunitary quantum trajectory Monte Carlo method for open quantum systems

We have developed a generalized nonunitary Lindblad equation and its quantum trajectory Monte Carlo implementation for the evolution of open quantum systems (OQSs) whose coupling to the environment features not only energy exchange but also probability flux to the environment. This generalization allows the treatment of a class of problems where the state space of the system includes bound and continuum states. We show the equivalence between the solution of the generalized Lindblad equation and the Monte Carlo average over open quantum trajectories. As a first test case we study the multilevel radiative decay of a hydrogenic ion. As a second test case we apply the theory to the time development of the internal state of fast highly charged Kr³⁵⁺ ions traversing carbon foils with varying thickness subject to collisions and to spontaneous radiative decay. We find significantly improved agreement of the nonunitary transport theory with experimental data.