A hybrid stochastic hierarchy equations of motion approach to treat the low temperature dynamics of non-Markovian open quantum systems

TL;DR

This paper introduces a hybrid stochastic hierarchical equations of motion (sHEOM) method that efficiently models low temperature non-Markovian open quantum systems, reducing computational cost and enabling treatment of larger systems.

Contribution

The paper develops a hybrid stochastic HEOM approach that overcomes low temperature challenges and improves convergence, expanding the applicability of non-Markovian quantum dynamics simulations.

Findings

Nearly temperature-independent numerical cost.

Fewer hierarchy tiers needed for convergence.

Accurate energy transfer and entanglement dynamics at low temperatures.

Abstract

The hierarchical equations of motion technique has found widespread success as a tool to generate the numerically exact dynamics of non-Markovian open quantum systems. However, its application to low temperature environments remains a serious challenge due to the need for a deep hierarchy that arises from the Matsubara expansion of the bath correlation function. Here we present a hybrid stochastic hierarchical equation of motion (sHEOM) approach that alleviates this bottleneck and leads to a numerical cost that is nearly independent of temperature. Additionally, the sHEOM method generally converges with fewer hierarchy tiers allowing for the treatment of larger systems. Benchmark calculations are presented on the dynamics of two level systems at both high and low temperatures to demonstrate the efficacy of the approach. Then the hybrid method is used to generate the exact dynamics of systems that are nearly impossible to treat by the standard hierarchy. First, exact energy transfer rates are calculated across a broad range of temperatures revealing the deviations from the Forster rates. This is followed by computations of the entanglement dynamics in a system of two qubits at low temperature spanning the weak to strong system-bath coupling regimes.