Strong Coupling Master Equation for Gaussian Noise

To analyze the decoherence effects during quantum annealing, theoretical tools are needed to probe the system dynamics in the strong coupling region. We proposed a master equation for Gaussian noise based on cumulant expansion techniques. Without the usual weak coupling assumption, this approach treats the system Hamiltonian as a perturbation to the system-bath term, which is exactly solvable. The result is compared with non-interacting blip approxiation(NIBA), which is the most commonly used technique to simulate the strong coupling region.