We formulate a Floquet-Markov Lindblad master equation for translationally cold two-level atoms driven by a strong monochromatic wave and coupled to a common electromagnetic bath. The resulting dipole-dipole interaction reproduces the anisotropic Heisenberg model.
We formulate a Floquet-Markov master equation, which combines an open quantum system approach with Floquet theory, for two spatially separated two-level atoms driven by a strong electromagnetic field and coupled to a common electromagnetic bath. This equation features a modified form of dipole-dipole interactions compared to the case of weakly driven atoms, giving rise to new, previously undescribed shifts of the Floquet quasienergies. We provide a detailed physical interpretation of the modified dipole-dipole interactions of two-level atoms, discuss their manifestations in two-atom resonance fluorescence, and extract the distance dependence of the dipole-dipole force between the atoms. The extensive discussion of two-level atoms is complemented by a brief study of one-dimensional hydrogen atoms (otherwise essentially described without approximations), with focus on the dipole-dipole interactions of periodically driven atoms whose electronic degrees of freedom are locked in non-dispersive wave packet states.
Periodically driven quantum systems are commonly modeled using master equations constructed in the eigenbasis of an undriven Hamiltonian, implicitly assuming that environmental dissipation couples to static energy transitions even under strong time-periodic driving. The validity of this approximation beyond weak or near-resonant driving remains poorly understood. To address the need for a more self-consistent quantum theory approach, we formulate a nonsecular Floquet--Markov generalized master equation (F-GME) in the quasienergy basis, treating interaction-induced (internal) and drive-induced (external) nonperturbative dressing on an equal footing. We subsequently investigate dissipation in two minimal driven open quantum systems---a harmonically driven two-level system and a harmonically driven coupled-two-level-system---each weakly coupled to a Markovian bath. Comparing the F-GME to a time-independent dressed-basis master equation, we show that even for a flat-bath spectral density and weak dissipation, the two approaches can yield qualitatively different steady-state populations and emission spectra. We resolve dissipation into drive-assisted sideband processes decaying via Floquet extended-space quasienergy channels, and show these channels can hybridize through nonsecular couplings into collective Floquet--Liouville modes governing observable spectral resonances. This analysis demonstrates that time-independent dissipative descriptions can incorrectly weight multiphoton Floquet transitions by collapsing quasienergy-resolved decay pathways into static energy gaps. The F-GME framework provides a systematic diagnostic for identifying regimes where Floquet-consistent dissipation is essential and clarifies the physical origin of discrepancies between commonly used master-equation approaches.
The dynamics of open quantum systems is commonly described by quantum master equations derived under the assumption of weak system-bath coupling and a separation of timescales between system and bath. When the system is additionally subjected to a periodic driving, the validity of the resulting Floquet master equations is further restricted to regimes of weak or high-frequency driving. Here, we benchmark a set of commonly used Floquet master equations for a model of two locally driven spins coupled to a shared Ohmic reservoir at finite temperature. We systematically probe the accuracy of the equations as a function of the driving parameters, thus identifying limits of their applicability. Dynamical maps predicted by each master equation are compared against numerically exact non-Markovian simulations, tracking the full relaxation dynamics. We find that the accuracy of each master equation closely reflects the assumptions underlying its derivation. For the Floquet-Lindblad equation, errors can be strongly amplified near resonances where the secular approximation breaks down, while approaches that avoid the secular approximation perform better and exhibit a more systematic dependence of the error on driving frequency and amplitude.