Quantum irreversible decoherence behaviour in open quantum systems with few degrees of freedom. Application to 1H NMR reversion experiments in nematic liquid crystals.

HÉCTOR H. SEGNORILE; RICARDO C. ZAMAR

San Carlos de Bariloche

Congreso; 98ª Reunión Nacional de de Física de la AFA; 2013

AFA

An experimental study of NMR spin decoherence in nematic liquid crystals is presented [1]. The outcome of the experiments are analyzed in the framework of a theory that considers the spins as an open quantum system coupled to a quantum molecular environment, presented by the authors recently [2]. Decoherence dynamics can be put in evidence by means of refocusing experiments of the dipolar interactions. The experimental technique used in this work is based on the MREV8 [3-5] pulse sequence. Non-idealities of the experimental setting, like external field inhomogeneity, pulse misadjustments and the presence of non-reverted spin interaction terms are analysed in detail and their effects on the observed signal decay are estimated. It is found that, though all these non-idealities could in principle affect the evolution of the spin dynamics, their inuence can be mitigated and they do not present the characteristic behaviour of the irreversible spin decoherence. As unique characteristic of decoherence, the experimental results clearly show the occurrence of eigen-selectivity [2] in a time scale intermediate [6] between those controlled by quantum interference of the closed spin system and thermalization, in complete agreement with the theoretical predictions. We conclude that the eigen-selection effect is the fingerprint of decoherence associated with a quantum open spin system in liquid crystals. Besides,these features of the results account for the quasi-equilibrium states of the spin system, which were observed previously in these mesophases [7-11], and lead to conclude that the quasi-equilibrium is a definite stage of the spin dynamics during its evolution towards equilibrium.   [1] H. H. Segnorile, and R. C. Zamar, arXiv:1305.0973 (2013). [2] H.H. Segnorile, and R.C. Zamar. J. Chem. Phys. 135, 244509 (2011). [3] P. Mansfield. J. Phys. C 4, 1444 (1971). [4] W. K. Rhim, D. D. Elleman, and R. W. Vaughan. J. Chem. Phys. 58, 1772 (1973). [5] W. K. Rhim, D. D. Elleman, and R. W. Vaughan. J. Chem. Phys. 59, 3740 (1973). [6] C. E. González, H. H.Segnorile, and R. C. Zamar. Phys. Rev. E 83, 011705 (2011). [7] H. Schmiedel, S. Grande, and B. Hillner, Phys. Lett. 91A, 365 (1982). [8] O. Mensio, C. E. González, R. C. Zamar, D. J. Pusiol, and R. Y. Dong, Physica B 320, 416 (2002). [9] O. Mensio, C. E. González, and R. C. Zamar, Phys. Rev. E 71, 011704 (2005). [10] H. H. Segnorile, C. J. Bonin, C. E. González, R. H. Acosta, and R. C. Zamar, Solid State Nucl. Magn. Reson.36, 77 (2009). [11] L. Buljubasich, G. A. Monti, R. H. Acosta, C. J. Bonin, C. E. González, and R. C. Zamar, J. Chem. Phys.130, 024501 (2009).