Abstract
We consider the relaxation dynamics of two quantum levels coupled to a stochastic bath. We emphasize that even if the matrix elements of the fluctuating Hamiltonian are Gaussian, a second-order cumulant truncation is not exact. For various stochastic models, including the case of a spin-1/2 particle in a fluctuating magnetic field, we calculate 1/T 1, the population relaxation rate, and 1/T 2, the phase relaxation rate, up to fourth order in perturbation theory. We show that unlike the commonly accepted second-order result that 1/T 2⩾1/2T 1, when fourth-order terms are included, in some instances 1/T 2<1/2T 1.
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Budimir, J., Skinner, J.L. On the relationship betweenT 1 andT 2 for stochastic relaxation models. J Stat Phys 49, 1029–1042 (1987). https://doi.org/10.1007/BF01017558
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DOI: https://doi.org/10.1007/BF01017558