Open quantum system approach to transient coherence in ion-solid transport

We investigate the passage of highly charged ions through solids by means of classical and quantum transport theory. We focus on the time evolution of electronic states of hydrogenic projectile ions as they suffer multiple collisions and radiative decay inside the solid. We use a hybrid approach where the dynamics of electrons in highly excited projectile states and in the continuum is described by a classical transport theory while we adopt a quantum transport theory for the description of deeply bound states. For the evolution of open quantum systems (OQS) we have developed a generalized non-unitary Lindblad master equation and its quantum trajectory Monte Carlo implementation allowing for a description of non-unitary OQSs that are also open with respect to probability flux (i.e. electron capture and ionization). We apply the classical transport theory to the emission of electrons and investigate properties of the convoy electron peak. Within the quantum transport theory we focus on the evolution of deeply bound states. In a first application of the new theory we investigate transient coherences created by collisional excitation in transport of Kr35+ ions through a carbon target. We find improved agreement of the non-unitary transport theory with experimental data. In a second application we investigate transient coherences created in electron capture by an initially bare argon projectile and decoherence in further interaction with the solid. Electron capture populates a partially coherent superposition of hydrogenic projectile states while interaction with the environment (target atoms and electrons, radiative decay) results in collisional and dynamical mixing of populations and coherences as well as ionization. We compare nl populations during transport with measurements. In the limit of thin targets we can directly test electron capture cross sections against experimental findings while for thicker targets we have the opportunity to follow the dynamics of the open quantum system in interaction with the solid as a function of interaction time. The observed results are in close agreement with the experimental data confirming the accuracy of electron capture cross sections as well as the description of the time evolution within the OQS approach. (author)