Prethermalization in open quantum systems: an application of the fluctuation-regulated quantum master equation

Quantum master equations (QME) describe the nonequilibrium dynamics of open quantum systems. For systems that are weakly coupled to a nearly memoryless bath, Markovian QMEs are routinely used. Markovian QMEs include the drive terms in the first order and the system-bath coupling in the second order. Here we show that such QMEs can be extended to incorporate the dissipative higher-order contributions from the drive, provided one takes into account the effects of thermal fluctuations in the local environment. Such an extension to the higher-order terms can also be done for other coupling terms, such as dipolar couplings. The resulting master equation is named a fluctuation-regulated quantum master equation (FRQME). For a driven-dipolar open quantum system for which the system-bath coupling is very small compared to the drive and the dipolar interaction, the system exhibits multiple timescales of evolution, with the system-bath relaxation timescale being the slowest one. We observe, in such a system, the dissipators from FRQME give rise to a set of quasi-conserved quantities. In a timescale much shorter than the relaxation timescale, these quasi-conserved quantities dominate the dynamics. The presence of these quasi-conserved quantities ensures constrained dynamics and results in the emergence of a prethermal state followed by unconstrained evolution under system-bath coupling. In the talk, we shall discuss the dynamics of this driven dipolar system with the principal focus on the emergence of the prethermal state.