The open driven two-level system at conical intersections of quasienergies

Area of Science:

• Quantum mechanics
• Condensed matter physics
• Statistical mechanics

Background:

• Investigating the stationary state of quantum systems is crucial for understanding their long-term behavior.
• Two-level systems are fundamental models in quantum physics, with applications in quantum computing and spectroscopy.
• Particle exchange with an environment introduces dissipation and decoherence, significantly altering system dynamics.

Purpose of the Study:

• To determine if Floquet state populations are governed by quasienergies or mean energies in an ac-driven two-level system.
• To explore the behavior near conical intersections of quasienergies where these energy definitions diverge.
• To identify temperature-driven transitions in the system's stationary state.

Main Methods:

• Theoretical analysis of an ac-driven two-level system coupled to a fermionic bath.
• Focus on parameter regimes near conical intersections of quasienergies.
• Numerical calculations to validate analytical estimates.

Main Results:

• A crossover is observed in the system's stationary state as a function of temperature.
• At low temperatures, the system exhibits a Floquet-Gibbs-like state.
• At intermediate temperatures, the system transitions to a state dominated by mean energy.

Conclusions:

• The system's stationary state is not solely determined by quasienergies or mean energies but exhibits a temperature-dependent crossover.
• The vicinity of conical intersections is key to observing distinct behaviors related to quasienergies and mean energies.
• Findings provide insights into thermalization and energy dynamics in open quantum systems.