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Due to the limited sensitivity of many nuclear magnetic resonance (NMR) applications, careful consideration must be given to the effect of NMR data processing on spectral noise. This work presents analytical relationships as well as simulated and experimental results characterizing the propagation of noise by unsymmetric covariance NMR processing, which concatenates two NMR spectra along a common dimension, resulting in a new spectrum showing spin correlations as cross peaks that are not directly measured in either of the two input spectra. It is shown how the unsymmetric covariance spectrum possesses an inhomogeneous noise distribution across the spectrum with the least amount of noise in regions whose rows and columns do not contain any cross or diagonal peaks and with the largest amount of noise on top of signal peaks. Therefore, methods of noise estimation commonly used in Fourier transform spectroscopy underestimate the amount of uncertainty in unsymmetric covariance spectra. Different data processing procedures, including the Z-matrix formalism, thresholding, and maxima ratio scaling, are described to assess noise contributions and to reduce noise inhomogeneity. In particular, determination of a Z score, which measures the difference in standard deviations of a statistic from its mean, for each spectral point yields a Z matrix, which indicates whether a given peak intensity above a threshold arises from the covariance of signals in the input spectra or whether it is likely to be caused by noise. Application to an unsymmetric covariance spectrum, obtained by concatenating two 2D 13C–1H heteronuclear, single quantum coherence (HSQC) and 13C–1H heteronuclear, multiple bond correlation (HMBC) spectra of a metabolite mixture along their common proton dimension, reveals that for sufficiently sensitive input spectra the reduction in sensitivity due to covariance processing is modest. [ABSTRACT FROM AUTHOR]

The results of extensive transport studies in localized regime of mesoscopic two-dimensional electron systems (2DES) with varying disorder are presented. A quick overview of previously achieved result is given. The main focus is on the observation of density dependent instabilities manifested by strong resistance oscillations induced by high perpendicular magnetic fields B⊥. While the amplitude of the oscillations is strongly enhanced with increasing B⊥, their position in electron density remains unaffected. The temperature dependence of resistivity shows a transition from an activated behaviour at high temperature to a saturated behaviour at low T. In the positions of resistance minima, the T dependence can even become metal-like (dρ/dT > 0). The activation energies obtained from the high T behaviour exhibit a formation of plateaux in connection with the resistance oscillations when analyzed as a function of electron density. We suggest the interplay between a strongly interacting electron phase and the background disorder as a possible explanation for our observation. [ABSTRACT FROM AUTHOR]

Abstract: We report an universal behaviour of hopping transport in strongly interacting mesoscopic two-dimensional electron systems (2DES). In a certain window of background disorder, the resistivity at low perpendicular magnetic fields follows the expected relation . The prefactor decreases exponentially with increasing electron density but saturates to a finite value at higher densities. Strikingly, this value is found to be universal when expressed in terms of absolute resistance and and shows quantisation at and . We suggest a strongly correlated electronic phase as a possible explanation. [Copyright &y& Elsevier]

Abstract: Geometric phase has been proposed as one of the promising methodologies to perform fault tolerant quantum computations. However, since decoherence plays a crucial role in such studies, understanding of mixed state geometric phase has become important. While mixed state geometric phase was first introduced mathematically by Uhlmann, recently Sjöqvist et al. [Phys. Rev. Lett. 85 (14) (2000) 2845] have described the mixed state geometric phase in the context of quantum interference and shown theoretically that the visibility as well as the shift of the interference pattern are functions of geometric phase and the purity of the mixed state. Here we report the first experimental study of the dependence of interference visibility and shift of the interference pattern on the mixed state geometric phase by nuclear magnetic resonance. [Copyright &y& Elsevier]

Abstract: Quantum adiabatic algorithm is a method of solving computational problems by evolving the ground state of a slowly varying Hamiltonian. The technique uses evolution of the ground state of a slowly varying Hamiltonian to reach the required output state. In some cases, such as the adiabatic versions of Grover’s search algorithm and Deutsch–Jozsa algorithm, applying the global adiabatic evolution yields a complexity similar to their classical algorithms. However, using the local adiabatic evolution, the algorithms given by J. Roland and N.J. Cerf for Grover’s search [J. Roland, N.J. Cerf, Quantum search by local adiabatic evolution, Phys. Rev. A 65 (2002) 042308] and by Saurya Das, Randy Kobes, and Gabor Kunstatter for the Deutsch–Jozsa algorithm [S. Das, R. Kobes, G. Kunstatter, Adiabatic quantum computation and Deutsh’s algorithm, Phys. Rev. A 65 (2002) 062301], yield a complexity of order (where N =2 n and n is the number of qubits). In this paper, we report the experimental implementation of these local adiabatic evolution algorithms on a 2-qubit quantum information processor, by Nuclear Magnetic Resonance. [Copyright &y& Elsevier]

We report the observation of linear magneto-resistance (LMR) with a very low cross-over magnetic field (Bc) at room temperature in bismuth(110) thin films fabricated using thermal evaporation. The magneto-resistance at different temperatures (T) indicate that Bc has a strong T-dependence, and displays a remarkably small magnitude of 180 mT at T = 300 K. The parameter Φ, defined as the MR% (B = 1 T)/ Bc is 248, is considerably higher at room temperature compared to values previously reported in literature. The observed LMR is likely due to the recombination of carriers in compensated systems near charge neutrality. Our measurements demonstrate that the LMR can be observed at a very low field and high T, which can be utilized in a variety of applications. [ABSTRACT FROM AUTHOR]

We report a detailed study on low-frequency 1/f -noise in large-area molecular-beam epitaxy grown thin (~10 nm) films of topological insulators as a function of temperature, gate voltage, and magnetic field. When the Fermi energy is within the bulk valence band, the temperature dependence reveals a clear signature of generation-recombination noise in the defect states in the bulk band gap. However, when the Fermi energy is tuned to the bulk band gap, the gate voltage dependence of noise shows that the resistance fluctuations in surface transport are caused by correlated mobility-number density fluctuations due to the activated defect states present in the bulk of the topological insulator crystal with a density of Dit =3:2× 1017 cm-2 eV-1. In the presence of the magnetic field, noise in these materials follows a parabolic dependence, which is qualitatively similar to mobility and charge-density fluctuation noise in non-degenerately doped trivial semiconductors. Our studies reveal that even in thin films of (Bi,Sb)2Te3 with thickness as low as 10 nm, the internal bulk defects are the dominant source of noise. [ABSTRACT FROM AUTHOR]

We investigate the Nernst effect in a mesoscopic two-dimensional electron system (2DES) at low magnetic fields, before the onset of Landau level quantization. The overall magnitude of the Nernst signal agrees well with semiclassical predictions. We observe reproducible mesoscopic fluctuations in the signal that diminish significantly with an increase in temperature. We also show that the Nernst effect exhibits an anomalous component that is correlated with an oscillatory Hall effect. This behavior may be able to distinguish between different spin-correlated states in the 2DES. [ABSTRACT FROM AUTHOR]

We report on the fabrication and characterization of a device which allows the formation of an antidot lattice (ADL) using only electrostatic gating. The antidot potential and Fermi energy of the system can be tuned independently. Well defined commensurability features in magnetoresistance as well as magnetothermopower are observed. We show that the thermopower can be used to efficiently map out the potential landscape of the ADL. [ABSTRACT FROM AUTHOR]

Engineering devices with a large electrical response to magnetic field is of fundamental importance for a range of applications such as magnetic field sensing and magnetic read heads. We show that a colossal nonsaturating linear magnetoresistance (NLMR) arises in two-dimensional electron systems hosted in a GaAs/AlGaAs heterostructure in the strongly insulating regime. When operated at high source-drain bias, the magnetoresistance of our devices increases almost linearly with magnetic field, reaching nearly 10 000% at 8 T, thus surpassing many known nonmagnetic materials that exhibit giant NLMR. The temperature dependence and mobility analysis indicate that the NLMR has a purely classical origin, driven by nanoscale inhomogeneities. A large NLMR combined with small device dimensions makes these systems an attractive candidate for on-chip magnetic field sensing. [ABSTRACT FROM AUTHOR]