Numerically efficient quasi-adiabatic propagator path integral approach with two independent non-commuting baths

Area of Science:

• Quantum mechanics
• Computational physics
• Chemical physics

Background:

• Path integral methods, like QUAPI, are crucial for simulating open quantum systems.
• QUAPI's computational cost grows exponentially with system size and time, limiting its application.
• Multiple non-commuting environments exacerbate these computational challenges.

Purpose of the Study:

• To evaluate the efficiency and accuracy of QUAPI approximations for systems with two independent, non-commuting environments.
• To investigate the impact of approximations like memory cutoff, path filtering, and coarse-graining.
• To analyze the behavior of a pure dephasing environment coupled with another non-commuting environment.

Main Methods:

• Applied approximations to the QUAPI method for a two-bath system.
• Investigated sharply defined memory cutoff, path filtering, and mask-assisted coarse-graining.
• Analyzed scenarios with one pure dephasing bath and another non-commuting bath.

Main Results:

• Path filtering is not directly transferable to two-bath systems, even in weak-coupling limits.
• Mask-assisted coarse-graining effectively handles sharply defined memory cutoffs.
• The assumption of additive environments breaks down when system-bath coupling operators do not commute.

Conclusions:

• The quasi-Markovian nature of a pure dephasing bath can be lost in the presence of other non-commuting fluctuations.
• Care must be taken when applying approximations designed for single environments to multi-bath systems.
• New computational strategies are needed for accurate simulations of open quantum systems with complex environments.