A study of the relaxation dynamics in a quadrupolar NMR system using Quantum State Tomography

This article reports a relaxation study in an oriented system containing spin 3/2 nuclei using quantum state tomography (QST). The use of QST allowed evaluating the time evolution of all density matrix elements starting from several initial states. Using an appropriated treatment based on the Redfield theory, the relaxation rate of each density matrix element was measured and the reduced spectral densities that describe the system relaxation were determined. All the experimental data could be well described assuming pure quadrupolar relaxation and reduced spectral densities corresponding to a superposition of slow and fast motions. The data were also analyzed in the context of Quantum Information Processing, where the coherence loss of each qubit of the system was determined using the partial trace operation. (C) 2008 Elsevier Inc. All rights reserved.

NUCLEAR SPIN 3/2 ELECTRIC QUADRUPOLE RELAXATION AS A QUANTUM COMPUTATION PROCESS

In this work we applied a quantum circuit treatment to describe the nuclear spin relaxation. From the Redfield theory, we obtain a description of the quadrupolar relaxation as a computational process in a spin 3/2 system, through a model in which the environment is comprised by five qubits and three different quantum noise channels. The interaction between the environment and the spin 3/2 nuclei is described by a quantum circuit fully compatible with the Redfield theory of relaxation. Theoretical predictions are compared to experimental data, a short review of quantum channels and relaxation in NMR qubits is also present.

On the Relaxation Mechanisms of 6-Azauracil

The nonadiabatic photochemistry of 6-azauracil has been studied by means of the CASPT2//CASSCF protocol and double-zeta plus polarization ANO basis sets. Minimum energy states, transition states, minimum energy paths, and surface intersections have been computed in order to obtain an accurate description of several potential energy hypersurfaces. It is concluded that, after absorption of ultraviolet radiation (248 nm), two main relaxation mechanisms may occur, via which the lowest (3)(pi pi*) state can be populated. The first one takes place via a conical intersection involving the bright (1)(pi pi*) and the lowest (1)(n pi*) states, ((1)pi pi*/(1)n pi*)(CI), from which a low energy singlet-triplet crossing, ((1)n pi*/(3)pi pi*)(STC), connecting the (1)(n pi*) state to the lowest (3)(pi pi*) triplet state is accessible. The second mechanism arises via a singlet-triplet crossing, ((1)pi pi*/(3)n pi*)(STC), leading to a conical intersection in the triplet manifold, ((3)n pi*/(3)pi pi*)(CI), evolving to the lowest (3)(pi pi*) state. Further radiationless decay to the ground state is possible through a (gs/(3)pi pi*)(STC).

FT-Raman, FTIR and density functional theory studies of a hydrogen-bonded formamide: pyridine complex

Raman and IR experiments have been carried out on formamide (FA) and pyridine (Py) mixtures at different compositions. The appearance of a new Raman band at 996 cm(-1) (nu(1) region of Py), whose intensity depends on the FA concentration, is assigned to an FA: Py adduct and this result is in excellent agreement with those of other authors who employed noisy light-based coherent Raman scattering spectroscopy (I((2)) CARS). Another band at 1587 cm(-1) (nu(8) region of Py) has been observed for the first time by using Raman and IR spectroscopies. Its intensity shows the same dependence on the FA concentration and this fact allows us to also attribute it to an FA: Py adduct. The good relationship between the Raman and IR data demonstrates the potential of the vibrational spectroscopy for this kind of study. Owing to higher absolute Raman scattering cross section, the nu(1) region of Py has been chosen for the quantitative analysis and a stoichiometry of 1 : 1 FA: Py is reported. The experimental data are very well supported by the density functional theory (OFT) calculation, which was employed for the first time to the present system. Furthermore, the actual investigation shows an excellent agreement with those reported from computational calculations for similar systems. A comparison with our previous studies confirms that: the solvent dielectric constant determines the stoichiometry of a given Lewis acid-base adduct in the infinite dilution limit. Copyright (C) 2009 John Wiley & Sons, Ltd.