Speaker
Description
Description of quantum coupling is a universal problem appearing in many different fields (NMR, quantum computing, molecular and atomic physics,...). In particle physics, it applies to particle mixing, underlying neutrino oscillations and resonant particle production (applicable beyond these two) in different environments, of great importance in many BSM scenarios. I will discuss non-adiabatic transitions in the simplest two-state coupled quantum system. An analytical description is traditionally provided by the Landau-Zener-Stuckelberg-Majorana (LZSM) approximation. However, in many applications, such as various cosmological problems, a time dependent mixing and interactions with the environment, where thermal effects and decoherence play an important role, have to be considered, requiring an extension of the LZSM approach. I will show how a density matrix formalism provides a powerful tool for treating such a problem. I will show some general analytic results that reproduce LZSM approximation in the appropriate limit but also generalise it when a time-dependent mixing is considered (decoherence can also be included, I will show results in the absence of decoherence for simplicity). I will finally comment on a comparison with existing numerical results.