arXiv:2108.07248 · Quantum

Environment-assisted strong coupling regime

Timofey T. Sergeev, I. V. Vovchenko, A. A. Zyablovsky, E. S. Andrianov

Published Apr 13, 2022• 11 citations

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.

DOI: 10.22331/q-2022-04-13-684

Related papers

Interaction with environment as a source of ultra-strong coupling

Timofey T. Sergeev, I. V. Vovchenko, A. A. Zyablovsky +1 more

In this letter, we demonstrate that in both classical and quantum open systems, the Hamiltonian interaction between subsystems, along with relaxations caused by the interaction with reservoirs, results in the appearance of effective non-Hermitian coupling. It is determined by a gradient of density of states of reservoirs. We show that for a power-law frequency dependence of the density of states, the non-Hermitian coupling is proportional to a product of the Hermitian coupling strength and the relaxation rates. As a result, this non-Hermitian coupling begins to play a crucial role with increasing Hermitian coupling strength between the subsystems and leads to a qualitative change in the behavior of non-Hermitian systems. Namely, when the Hermitian coupling strength exceeds a critical value, the non-Hermitian coupling becomes so large that it guarantees that the system is in the strong coupling regime at any relaxation rate. This critical coupling can be associated with the transition point to the ultra-strong coupling regime, which, until now, has not been defined exactly.

Aug 16, 20210 citations

Self-consistent description of relaxation processes in systems with ultra- and deep-strong coupling

Timofey T. Sergeev, A. A. Zyablovsky, E. S. Andrianov +1 more

An ultra-strong coupling regime takes place in a compound system when a coupling strength between the subsystems exceeds one-tenth of the system eigenfrequency. It transforms into a deep-strong coupling regime when the coupling strength exceeds the system eigenfrequency. In these regimes, there are difficulties with the description of relaxation processes without explicit consideration of environmental degrees of freedom. To correctly evaluate the relaxation rates, it is necessary to consider the interaction of the system with its environment taking into account the counter-rotating wave and diamagnetic terms. We develop a self-consistent theory for the calculation of the relaxation rates in the systems, in which the coupling strength is of the order of the system eigenfrequency. We demonstrate that the increase in the coupling strength can lead to a significant decrease in the relaxation rates. In particular, we show that, for frequency-independent density of states of the environment, the relaxation rates decrease exponentially with the increase in the coupling strength. This fact can be used to suppress losses by tuning the strength coupling and the environment states.

arXiv:2303.18159Journal of the Optical Society of America BSep 15, 20230 citations

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

I. V. Vovchenko, A. A. Zyablovsky, A. A. Pukhov +1 more

Recently, strong coupling between non-Hermitian physical systems of different nature is widely investigated due to it endows them with new properties. In this work, we investigate the energy transport between strongly coupled systems. We use a partial-secular approach for the description of an open quantum system to investigate the system dynamics during the transition from a weak to a strong coupling regime with an increase of coupling between subsystems. On the example of strongly coupled two-level atoms, we show that near the transition point enhancement of energy transport between the system and reservoirs takes place. This manifests in the fact that energy flow normalized to the coupling constant reaches the maximum both in the cases of zero and non-zero frequency detuning. We show that maximization of normalized energy flow can be used for the determination of the transition to the strong coupling regime in the case of non-zero detuning when there is no clear transition point from the weak to strong coupling regime. The suppression of the energy flow at high relaxation is demonstrated.

arXiv:2211.08484Nov 15, 20220 citations

Quantum speedup dynamics process in multiqubit-interacting system

Ji-Yang Sun, Kai Dong Xu, Zai-Dong Li

We investigate the dynamics of an N -qubit interacting system coupled to a common reservoir. In the weak system-environment coupling regime, the crossovers from Markovian to non-Markovian and from no speedup to speedup can be realized by adjusting the controllable parameters (i.e., the coupling strength between qubits and the number of the qubits). However, in the case of strong coupling, the multiple transitions from non-Markovian regime to Markovian regime and from speedup to no speedup can be induced by manipulating controllable parameters. In addition, a phenomenon can be noticed that the number of qubits and the coupling strength between the qubits have the different effect on the non-Markovian dynamics and speedup evolution of the system in the above weak- and strong-coupling regimes. Our results provide an effective theoretical scheme for the realization of non-Markovian speedup dynamic processes. Published by the American Physical Society 2024

Physical Review ResearchMar 22, 20244 citations

Effects of initial environmental correlations in the dynamics of open systems

Zhong‐Xiao Man, Nguyen Ba An, Yun‐Jie Xia

In this work, we study the effects of different forms of correlations of environments on the dynamics of open systems’ entanglement and discord. We consider two two-level atoms A and B interacting, respectively with two spatially separated modes a and b, each of which is in turn surrounded by a dissipative reservoir. The two modes may initially be in an entangled or classically correlated or product state with their marginal state being the same in all the cases. We compare the power of different environmental correlation forms in the revival of the atoms’ entanglement and discord in the strong atom–mode coupling regime. We also show how the dynamical behavior of the atoms’ entanglement and discord nontrivially change by the presence of initial environmental correlation in the weak atom–mode coupling regime. Finally, we reveal that initial entanglement between the modes can induce correlations between initially uncorrelated atoms.

Journal of the Optical Society of America BApr 2, 20135 citations

Equilibrium states of open quantum systems in the strong coupling regime

Yiğit Subaşı, Christen H. Fleming, Jacob M. Taylor +1 more

In this work we investigate the late-time steady states of open quantum systems coupled to a thermal reservoir in the strong coupling regime. In general such systems do not necessarily relax to a Boltzmann distribution if the coupling to the thermal reservoir is nonvanishing or equivalently if the relaxation time scales are finite. Using a variety of nonequilibrium formalisms valid for non-Markovian processes, we show that starting from a product state of the closed system = system+environment, with the environment in its thermal state, the open system which results from coarse graining the environment will evolve towards an equilibrium state at late times. This state can be expressed as the reduced state of the closed system thermal state at the temperature of the environment. For a linear (harmonic) system and environment, which is exactly solvable, we are able to show in a rigorous way that all multitime correlations of the open system evolve towards those of the closed system thermal state. Multitime correlations are especially relevant in the non-Markovian regime, since they cannot be generated by the dynamics of the single-time correlations. For more general systems, which cannot be exactly solved, we are able to provide a general proof that all single-time correlations of the open system evolve to those of the closed system thermal state, to first order in the relaxation rates. For the special case of a zero-temperature reservoir, we are able to explicitly construct the reduced closed system thermal state in terms of the environmental correlations.

arXiv:1206.2707Physical Review EDec 26, 201287 citations