Dissipative features of the driven spin-fermion system

TL;DR

This paper investigates a driven spin-fermion system coupled to metallic leads, revealing robustness of asymptotic states against system-bath coupling and the enhancement of quantum coherence through dissipation.

Contribution

It introduces a numerically exact method to simulate the real-time dynamics of a driven spin-fermion model beyond the Markovian limit and uncovers the interplay between driving, bath structure, and dissipation.

Findings

Asymptotic Floquet states are insensitive to system-bath coupling strength.

Chemical potential difference significantly influences system behavior.

Strong dissipation can enhance quantum coherence under certain driving conditions.

Abstract

We study a generic spin-fermion model, where a two-level system (spin) is coupled to two metallic leads with different chemical potentials, in the presence of monochromatic driving fields. The real-time dynamics of the system is simulated beyond the Markovian limit by an iterative numerically exact influence functional path integral method. Our results show that although both system-bath coupling and chemical potential difference contribute to dissipation, their effects are distinct. In particular, under certain drivings the asymptotic Floquet states of the system exhibit robustness against a range of system-bath coupling strength: the asymptotic behaviors of the system are insensitive to different system-bath coupling strength, while they are highly tunable by the chemical potential difference of baths. Further simulations show that such robustness may be essentially a result of the interplay between driving, bath electronic structure and system-bath coupling. Therefore the robustness could break down depending on the characteristics of the interplay. In addition, under fast linearly polarized driving the quantum stochastic resonance is demonstrated that stronger system-bath coupling (stronger dissipation) enhances rather than suppresses the amplitude of coherent oscillations of the system.