Evolution towards quasi-equilibrium in liquid crystals studied through decoherence of multiple-quantum coherences.

New evidence is presented in favor of irreversible decoherence as the mechanism which leads an initial out-of-equilibrium state to quasi-equilibrium. 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 spectra of the different coherences 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 decoherence, which indicates that the spin system in liquid crystal NMR experiments conforms an actual open quantum system.