More for LESS: Optimal Control of Open Quantum Systems Within the Born approximation

In the context of the Born approximation, i.e., neglecting system-environment correlations in the composite system state and assuming a time-independent environment state, we develop the dynamics of controlled, time-dependent quantum systems in the presence of irreversible environment-induced decoherence. We show that in the interaction picture, these dynamics separate the time evolution of the system into a sequence of unitary and nonunitary operations exactly. For state-dependent objectives, quantum optimal control is applied to the corresponding dynamical equations, and using a composite system model of interacting spins as an illustrative example, we find that simple and versatile controls are able to discover and use decoherence-free subspaces (when they exist) to optimize the state objectives. Results from several numerical control simulations will be presented and discussed. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. SAND2022-14340 A