LAUSR

Weakly nonlinear degrees of freedom in dissipative quantum systems tend to localize near manifolds of quasiclassical states. We present a family of analytical and computational methods for deriving optimal unitary model transformations that reduce the complexity of representing typical states. These transformations minimize the quantum relative entropy distance between a given state and particular quasiclassical manifolds. This naturally splits the description of quantum states into transformation coordinates that specify the nearest quasiclassical state and a transformed quantum state that can be represented in fewer basis levels. We derive coupled equations of motion for the coordinates and the transformed state and demonstrate how this can be exploited for efficient numerical simulation. Our optimization objective naturally quantifies the nonclassicality of states occurring in some given open system dynamics. This allows us to compare the intrinsic complexity of different open quantum systems.