A variational master equation approach to quantum dynamics with off-diagonal coupling in a sub-Ohmic environment

Area of Science:

• Quantum dynamics simulation
• Condensed matter physics
• Quantum information science

Background:

• Spin-boson models are crucial for understanding quantum dynamics in open systems.
• Simulating systems with both diagonal and off-diagonal couplings is computationally challenging.
• Understanding the role of bath spectral densities (Ohmic, sub-Ohmic) is key to controlling quantum phenomena.

Purpose of the Study:

• To develop and apply a master equation approach using an optimized polaron transformation for simulating spin-boson dynamics.
• To investigate the effects of simultaneous diagonal and off-diagonal spin-boson coupling.
• To explore the influence of Ohmic and sub-Ohmic bath spectral densities on system dynamics and coherence.

Main Methods:

• Utilized a master equation approach with an optimized polaron transformation.
• Simulated dynamics for systems with simultaneous diagonal and off-diagonal spin-boson coupling.
• Considered both Ohmic and sub-Ohmic bath spectral density functions.

Main Results:

• Off-diagonal coupling leads to system localization (non-zero population difference at long times).
• Off-diagonal coupling restrains coherent dynamics, particularly in the sub-Ohmic case.
• The developed method extends to stronger coupling regimes, enabling investigation of coherent-incoherent transitions.
• Phase diagrams reveal that sub-Ohmic environments support coherent dynamics at higher temperatures compared to Ohmic environments.

Conclusions:

• The optimized polaron transformation master equation is effective for simulating complex spin-boson dynamics.
• Off-diagonal coupling significantly impacts system localization and coherence.
• Sub-Ohmic environments offer advantages for maintaining quantum coherence at elevated temperatures.