Evolution towards quasi-equilibrium in nematic liquid crystals studied through decoherence of multi-spin multiple-quantum coherences

TL;DR

This study demonstrates that irreversible decoherence drives the transition to quasi-equilibrium in nematic liquid crystals, using NMR techniques to visualize multi-spin coherence evolution and eigen-selection effects.

Contribution

It provides experimental evidence linking irreversible decoherence to quasi-equilibrium formation in liquid crystals through advanced NMR methods.

Findings

Spectra amplitude decreases with reversion time

Decay is frequency selective

Eigen-selection indicates irreversible decoherence

Abstract

New evidence is presented in favor of irreversible decoherence as the mechanism which leads an initial out-of-equilibrium state to quasi-equilibrium in nematic liquid crystals. The NMR experiment combines the Jeener-Broekaert sequence with reversal of the dipolar evolution and decoding of multiple-quantum coherences to allow visualizing the evolution of the multi-spin coherence spectra during the formation of the quasi-equilibrium states. We vary the reversion strategies and the preparation of initial states and observe that the spectra amplitude attenuate with the reversion time, and notably, that the decay is frequency selective. We interpret this effect as evidence of "eigen-selection", a signature of the occurrence of irreversible adiabatic decoherence, which indicates that the spin system in liquid crystal NMR experiments conforms an actual open quantum system.