Dynamical stability of the one-dimensional rigid Brownian rotator: The role of the rotator's spatial size and shape

TL;DR

This paper studies how the size and shape of a one-dimensional rigid Brownian rotator affect its dynamical stability, revealing complex size-dependent criteria and quantum effects influencing the transition from quantum to classical behavior.

Contribution

It introduces a detailed analysis of size and shape effects on the stability of a quantum rotator using the Caldeira-Leggett master equation, highlighting complex criteria for stability.

Findings

Larger standard deviations reduce rotational stability.

No simple rules for stability; multiple size-related criteria exist.

Quantum corrections influence the quantum-classical transition.

Abstract

We investigate dynamical stability of a single propeller-like shaped molecular cogwheel modelled as the fixed-axis rigid rotator. In the realistic situations, rotation of the finite-size cogwheel is subject of the envi- ronmentally-induced Brownian-motion effect that we describe by utilizing the quantum Caldeira-Leggett master equation, in the weak-coupling limit. Assuming the initially narrow (classical-like) standard deviations for the an- gle and the angular momentum of the rotator, we investigate dynamics of the first and second moments depending on the size, i.e., on the number of blades of both the free rotator as well as of the rotator in the external har- monic field. The larger the standard deviations, the less stable (i.e. less pre- dictable) rotation. We detect the absence of the simple and straightforward rules for utilizing the rotator's stability. Instead, a number of the size-related criteria appear whose combinations may provide the optimal rules for the ro- tator dynamical stability and possibly control. In the realistic situations, the quantum-mechanical corrections, albeit individually small, may effectively prove non-negligible, and also revealing subtlety of the transition from the quantum to the classical dynamics of the rotator. As to the latter, we detect a strong size-dependence of the transition to the classical dynamics beyond the quantum decoherence process.