Environmental dynamics and the emergence of noncanonical equilibrium states in open quantum systems

Standard open quantum system methods eliminate all information on the environmental state in order to provide a tractable description of the system dynamics. By incorporating a collective coordinate of the environment into the system Hamiltonian, we develop a formalism that circumvents this limitation, allowing straightforward access to important properties of the environmental dynamics that are typically inaccessible using other methods. Focussing on the non-perturbative problem of a quantum system coupled to a low frequency environment, we reveal that the canonical thermal system steady-state predicted by standard perturbative methods is almost always incorrect. We show this to be due to the generation of long-lasting system-environment correlations that persist into the steady-state, leading also to non-Gaussian environmental states. We can, nevertheless, fully characterise the system-environment steady-state as a thermal state of the combined system-collective coordinate Hamiltonian. We outline how the resulting noncanonical system steady-state could be investigated in ongoing experiments to study deviations from canonical thermodynamics, with direct relevance to molecular and solid-state nanosystems.