Several NMR quasi-invariants in proton spin cluster of liquid crystals

C. J. BONIN; H. H. SEGNORILE; C. E. GONZÁLEZ; R. C. ZAMAR

Águas de Lindóia, Sao Pablo

Congreso; XXXVI ENCONTRO NACIONAL DE FISICA DA MATÉRIA CONDENSADA: XXXVI Brazilian Meeting on Condensed Matter Physics; 2013

Sociedade Brasileira de Física

In nematic liquid crystals (LCs), only two (non-Zeeman) Nuclear Magnetic Resonance (NMR) Quasi-Invariants (QI) are in so far addressed in the existing literature, namely S and W. The former is a two-spin order while the latter is a multi-spin one containing at least up to 8-correlated spins. A priori, it is very difficult to anticipate if other QIs are also supported by small proton spin clusters like LCs. This work is aimed at providing experimental evidence on the existence of other observables QIs by using Jeener-Broekaert radio-frequency pulse (JB) sequence. Identifying the full set of QIs in a system and distinguishing the exact characterization of their operators could then allow for applying these QIs in the quantum information processing area, particularly due to their multi-spin-correlated character and to the fact that they are not affected by decoherence processes. QIs relax with the environment by means of slow spin-lattice processes. These characteristics make these QIs become potential candidates for their implementation as noiseless quantum memories and/or multi-spin quantum registers. This work presents a simple method to disentangle the QIs prepared with JB sequence in some protonated systems (powder adamantane (C10H16), gypsum (CaSO4.2H2O), and 5CB LC (4´-pentyl-4-biphenyl-carbonitrile C18H19N)) from the experiments. Numerical simulations of density matrix during QIs creation in a 4-spins-1/2 cluster as representative of a LC 5CB benzene molecule are also shown. QIs are expanded on a spherical tensor operator basis, which is very convenient from the NMR point of view. Simulations yielded unexpected scalar tensor operators (unperturbed and unobserved by JB sequence) in QIs, which indicates the possible presence of long-lived states in a multi-spin coupled system.