Trajectory Ensemble Methods Provide Single-Molecule Statistics for Quantum Dynamical Systems

The emergence of experiments capable of probing quantum dynamics atthe single-molecule level requires the development of new theoretical tools capable ofsimulating and analyzing these dynamics beyond an ensemble-averaged description. Inthis article, we present an efficient method for sampling and simulating the dynamics ofthe individual quantum systems that make up an ensemble and apply it to study thenonequilibrium dynamics of the ubiquitous spin-boson model. We generate anensemble of single-system trajectories, and we analyze this trajectory ensemble usingtools from classical statistical mechanics. Our results demonstrate that the dynamics ofquantum coherence is highly heterogeneous at the single-system level due to variationsin the initial bath configuration, which significantly affects the transient exchange ofcoherence between the system and its bath. We observe that single systems tend toretain coherence over time scales longer than that of the ensemble. We also compute anovel thermodynamic entanglement entropy that quantifies a thermodynamic drivingforce favoring system-bath entanglement.

Automated summary

New theoretical tools are needed to simulate and analyze quantum dynamics at the single-molecule level, and this article presents an efficient method for sampling and simulating individual quantum systems. The study found that quantum coherence dynamics is highly heterogeneous at the single-system level and single systems tend to retain coherence over longer time scales than ensembles. Additionally, a novel thermodynamic entanglement entropy was computed to quantify a thermodynamic driving force favoring system-bath entanglement.