Quantum Momentum Distribution and Quantum Entanglement in the Deep Tunneling Regime

TL;DR

This paper introduces a modified path integral molecular dynamics method to analyze the directional momentum distribution of quantum particles, revealing the role of quantum entanglement in deep tunneling regimes.

Contribution

It presents a new estimator and a variationally enhanced sampling technique to study quantum momentum distribution and entanglement effects in tunneling molecules.

Findings

No secondary feature in directional momentum distribution

Quantum entanglement explains the absence of this feature

Method successfully applied to Malonaldehyde at low temperature

Abstract

In this paper, we consider the momentum operator of a quantum particle directed along the displacement of two of its neighbors. A modified open-path path integral molecular dynamics is presented to sample the distribution of this directional momentum distribution, where we derive and use a new estimator for this distribution. Variationally enhanced sampling is used to obtain this distribution for an example molecule, Malonaldehyde, in the very low temperature regime where deep tunneling happens. We find no secondary feature in the directional momentum distribution, and that its absence is due to quantum entanglement through a further study of the reduced density matrix.