Tagged particle dynamics in supercooled quantum liquid

TL;DR

This paper investigates how quantum effects alter the early-time dynamics of supercooled liquids, revealing deviations from classical behavior due to quantum uncertainty in particle positions.

Contribution

It introduces a quantum mode-coupling theory and simulations to analyze tagged particle dynamics, highlighting the impact of quantum uncertainty on initial ballistic motion.

Findings

Quantum uncertainty causes non-zero initial moments.

Increased quantumness weakens initial ballistic behavior.

Deviations from classical dynamics are significant at early times.

Abstract

We analyze dynamics of quantum supercooled liquids in terms of tagged particle dynamics. Unlike the classical case, uncertainty in the position of a particle in quantum liquid leads to qualitative changes. We demonstrate these effects in the dynamics of the first two moments of displacements, namely, the mean-squared displacement, $\langle \Delta r^2(t)\rangle$, and $\langle \Delta r^4(t)\rangle$. Results are presented for a hard sphere liquid using mode-coupling theory (MCT) formulation and simulation on a binary Lennard-Jones liquid. As the quantumness (controlled by the de-Broglie thermal wavelength) is increased, a non-zero value of the moments at zero time leads to significant deviations from the classical behavior in the initial dynamics. Initial displacement shows ballistic behavior $\langle \Delta r^2(t)\rangle\sim t^2$, but, as a result of large uncertainty in the position, the dynamical effects become weaker with increasing quantumness over this time scale.