Identifying differences between semi-classical and full-quantum descriptions of plexcitons

Abstract: Strong light-matter coupling between molecules and plasmonic nanoparticles give rise to new hybrid eigenstates of the coupled system, commonly referred to as polaritons, or more precisely, plexcitons. Over the last decade it has been amply shown that molecular electron dynamics and photophysics can be drastically affected by such interactions, thus paving the way for light-induced control of molecular excited-state properties and reactivity. Here, by combining ab initio molecular description and classical or quantum modelling of arbitrarily-shaped plasmonic nanostructures within Stochastic Schr\"odinger Equation, we present two approaches, one semi-classical and one full-quantum, to follow in real-time the electronic dynamics of plexcitons while realistically taking plasmonic dissipative losses into account. The full-quantum theory is compared with the semi-classical analogue under different interaction regimes, showing (numerically and theoretically) that even in the weak-field and weak-coupling limit a small-yet-observable difference arises.