Environment-assisted strong coupling regime

Abstract

Strong coupling regime takes place in open hybrid systems consisting of two or more physical subsystems when the coupling strength between subsystems exceeds the relaxation rate. The relaxation arises due to the interaction of the system with environment. For this reason, it is usually believed that the enhancement of the interaction with environment inevitably leads to a transition of the system from the strong to weak coupling regime. In this paper, we refute this common opinion. We demonstrate the interaction of the coupled system with environment induces an additional coupling between the subsystems that contribute to retention the system in the strong coupling regime. We show that the environmental-induced coupling strength is proportional to the product of the Rabi coupling strength by the gradient of the density of states of the reservoir. There is a critical Rabi coupling strength above which the environmental-induced coupling ensures that the system remains in the strong coupling regime at any relaxation rate. In this case, the strong coupling regime takes place even when the relaxation rate is significantly above the Rabi coupling strength between the subsystems. The critical coupling depends on the gradient of the reservoir density of states. We demonstrate that managing this gradient can serve as an additional tool to control the properties of the coupled systems.

Energy Transport Induced by Transition from Weak to Strong Coupling Regime Between Non-Hermitian systems

“…Thus, they are not applicable near the EP. As has been shown in [36,42], one can use PS approach which is valid near the EP and is reproduced local and global approaches when Ω γ and Ω γ, respectively.…”

“…When interaction between subsystems is large compared to relaxation rates and, as a consequence, splitting between eigenstates is larger than the relaxation rates, then the Lindblad superoperators are transition operators between the eigenstates of the Hamiltonian H S of interacting subsystems [28,38] In the intermediate case, when the splitting between the eigenstates are comparable with the relaxation rates, one can use PS approach [35,36] which takes into account the terms in the master equation which oscillate at the Rabi interaction frequency. Moreover, PS approach results in crossrelaxation processes, when the state of one subsystems influences on relaxation of another subsystems [42].…”

“…From the master equation for the system density matrix (1), one can obtain the equation for the expected values of any system operators  as d  /dt = Tr Â∂ ρ/∂t . For example, if one consider two coupled oscillators or TLSs and the amplitudes of their excitation, then the equations describing amplitude' dynamics, obtained in the local approach, predict the existence of an EP [1,41,42]. At the same time, the global approach does not predict the EP found in local approach.…”

“…At the same time, the global approach does not predict the EP found in local approach. PS approach reproduces only the signature of the EP [36,41,42]. The last means that instead of the point of eigenvalue' coincidence there is an inflection point in the dependence of the system eigenvalues on the coupling constant.…”

Signature of exceptional point phase transition in Hermitian systems

“…In this case, the interaction of the oscillators with the reservoirs leads to an exponential decay of the oscillators amplitudes (Figure 2a). In the Born-Markovian approximation and T = 0, the system dynamics are described by the effective non-Hermitian equation [52,55]:…”