Nonclassical correlation in NMR quadrupolar systems

The existence of quantum correlation (as revealed by quantum discord), other than entanglement and its role in quantum-information processing (QIP), is a current subject for discussion. In particular, it has been suggested that this nonclassical correlation may provide computational speedup for some quantum algorithms. In this regard, bulk nuclear magnetic resonance (NMR) has been successfully used as a test bench for many QIP implementations, although it has also been continuously criticized for not presenting entanglement in most of the systems used so far. In this paper, we report a theoretical and experimental study on the dynamics of quantum and classical correlations in an NMR quadrupolar system. We present a method for computing the correlations from experimental NMR deviation-density matrices and show that, given the action of the nuclear-spin environment, the relaxation produces a monotonic time decay in the correlations. Although the experimental realizations were performed in a specific quadrupolar system, the main results presented here can be applied to whichever system uses a deviation-density matrix formalism.Comment: Published versio

Normalization procedure for relaxation studies in NMR quantum information processing

NMR quantum information processing studies rely on the reconstruction of the density matrix representing the so-called pseudo-pure states (PPS). An initially pure part of a PPS state undergoes unitary and non-unitary (relaxation) transformations during a computation process, causing a "loss of purity" until the equilibrium is reached. Besides, upon relaxation, the nuclear polarization varies in time, a fact which must be taken into account when comparing density matrices at different instants. Attempting to use time-fixed normalization procedures when relaxation is present, leads to various anomalies on matrices populations. On this paper we propose a method which takes into account the time-dependence of the normalization factor. From a generic form for the deviation density matrix an expression for the relaxing initial pure state is deduced. The method is exemplified with an experiment of relaxation of the concurrence of a pseudo-entangled state, which exhibits the phenomenon of sudden death, and the relaxation of the Wigner function of a pseudo-cat state.Comment: 9 pages, 5 figures, to appear in QI

Solid-state 13C NMR studies of activated carbons prepared from biomass using different chemical agents.

Activated carbons are largely employed in several chemical and physical processes nowadays, including water treatment, catalysis, gas storage and others [1]. The surface properties of the porous carbons are determinant for most of such applications. Oxygenated functional groups present at the edges of the aromatic lamellae are known to influence decisively the surface chemistry of these materials [2]. In this work, solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy was used for the analysis of a series of activated carbons prepared from a lignocellulosic precursor, using different chemical activating agents

NMR Relaxation by Redfield's equation in a spin system I=7/2I=7/2

Redfield's master equation is solved analytically for a nuclear system with spin $I=7/2$. The solutions of each density matrix element are computed using the irreducible tensor operator basis. The $^{133}$Cs nuclei of the caesium-pentadecafluorooctanoate molecule in a lyotropic liquid crystal sample at the nematic phase and at room temperature was used as an experimental setup. Experimental longitudinal and transverse magnetization dynamics of the $^{133}$Cs nuclei signal were monitored and by numerical procedures the theoretical approach generates valuable mathematical expressions with the highest accuracy. The methodology introduced could be extended without major difficulties to other nuclei species

Experimentally Witnessing the Quantumness of Correlations

The quantification of quantum correlations (other than entanglement) usually entails laboured numerical optimization procedures also demanding quantum state tomographic methods. Thus it is interesting to have a laboratory friendly witness for the nature of correlations. In this Letter we report a direct experimental implementation of such a witness in a room temperature nuclear magnetic resonance system. In our experiment the nature of correlations is revealed by performing only few local magnetization measurements. We also compare the witness results with those for the symmetric quantum discord and we obtained a fairly good agreement