Open quantum dynamics theory for a complex subenvironment system with a quantum thermostat: Application to a spin...

Area of Science:

• Condensed matter physics
• Quantum dynamics
• Quantum information science

Background:

• Complex environments significantly influence dynamics in condensed phases.
• Simulating these environments is challenging due to numerous degrees of freedom.
• Existing models struggle to capture non-local, non-Gaussian noise characteristic of complex subenvironments.

Purpose of the Study:

• To develop and validate a novel quantum thermostat model for simulating quantum dynamics in complex environments.
• To investigate the impact of subenvironment properties, including quantum phase transitions, on a two-level system (TLS).
• To analyze decoherence and relaxation processes of a TLS interacting with a spin chain subenvironment.

Main Methods:

• A hybrid model combining a detailed subenvironment (1D XXZ spin chain) with a harmonic bath quantum thermostat.
• Simulation of a two-level system (TLS) dynamics interacting with the subenvironment.
• Utilizing hierarchical Schrödinger equations of motion for time-irreversible simulations at arbitrary temperatures.

Main Results:

• Observed decoherence of the TLS at finite temperatures, even under extreme spin anisotropy conditions.
• Demonstrated that subenvironment noise is spatially non-local and non-Gaussian, defying simple fluctuation-dissipation theorem characterization.
• Found complex changes in TLS population-relaxation dynamics correlating with spin anisotropy and magnetic ordering (ferromagnetic/antiferromagnetic).

Conclusions:

• The quantum thermostat model provides a viable approach for simulating quantum dynamics in complex, many-body environments.
• Subenvironment properties, particularly quantum phase transitions, critically affect TLS dynamics like decoherence and relaxation.
• The model captures intricate environmental effects beyond standard approximations, offering insights into quantum processes in realistic systems.