Quantum revivals and magnetization tunneling in effective spin systems

TL;DR

This paper explores the quantum dynamics of effective spin systems, focusing on quantum revival times and magnetization tunneling, revealing differences between wave-function and expectation value revivals and proposing new measurement methods.

Contribution

It introduces a refined definition of quantum revival times in spin systems and links revival phenomena to magnetization tunneling, enhancing understanding of quantum spin dynamics.

Findings

Revival times differ between wave-functions and expectation values.

Integer spins have coinciding revival times, unlike half-integer spins.

Shortest revival times occur at specific anisotropy-to-field ratios.

Abstract

Quantum mechanical objects or nanoobjects have been proposed as bits for information storage. While time-averaged properties of magnetic, quantum-mechanical particles have been extensively studied experimentally and theoretically, experimental investigations of the real time evolution of magnetization in the quantum regime were not possible until recent developments in pump-probe techniques. Here we investigate the quantum dynamics of effective spin systems by means of analytical and numerical treatments. Particular attention is paid to the quantum revival time and its relation to the magnetization tunneling. The quantum revival time has been initially defined as the recurrence time of a total wave-function. Here we show that the quantum revivals of wave-functions and expectation values in spin systems may be quite different which gives rise to a more sophisticated definition of the quantum revival within the realm of experimental research. Particularly, the revival times for integer spins coincide which is not the case for half-integer spins. Furthermore, the quantum revival is found to be shortest for integer ratios between the on-site anisotropy and an external magnetic field paving the way to novel methods of anisotropy measurements. We show that the quantum tunneling of magnetization at avoided level crossing is coherent to the quantum revival time of expectation values, leading to a connection between these two fundamental properties of quantum mechanical spins.