Detection of Quasi-equilibrium using Jeener-Broekaert experiment combined with multiple-quantum coherence spectra measurement under spin-reversion dynamics

We present an NMR experiment to detect the evolution of a spin system during the transient to a quasi-equilibrium state. In this way, new evidence is presented in favor of irreversible decoherence as the mechanism which leads an initial out-of-equilibrium state to quasi-equilibrium. The results are obtained using a modified Jeener-Broekaert experiment where a spin reversion pulse sequence and a decode of coherence are included. The sequence also allows visualizing the evolution of the full spectra of the different coherences during the formation of the quasi-equilibrium. We use different reversion strategies on three nematic liquid crystal samples. We conclude that the eigen-selection observed as an evidence of irreversible decoherence is an indication that the spin system in liquid-crystal NMR experiments, conform actual quantum open systems, where the quasi-equilibrium is a rigorous description of their dynamics in a time-scale far earlier than thermal equilibrium.