NMR Quantum Logic Gates for Homonuclear Spin Systems

If NMR systems are to be used as practical quantum computers, the number of coupled spins will need to be so large that it is not feasible to rely on purely heteronuclear spin systems. The implementation of a quantum logic gate imposes certain constraints on the motion of those spins not directly involved in that gate, the so-called "spectator" spins; they must be returned to their initial states at the end of the sequence. As a result, a homonuclear spin system where there is appreciable coupling between every pair of spins would seem to require a refocusing scheme that doubles in complexity and duration for every additional spectator spin. Fortunately, for the more realistic practical case where long-range spin-spin couplings can be neglected, simpler refocusing schemes can be devised where the overall duration of the sequence remains constant and the number of soft pulses increases only linearly with the number of spectator spins. These ideas are tested experimentally on a six qubit system: the six coupled protons of inosine.Comment: 11 pages LaTeX plus 6 fig

Hadamard NMR spectroscopy for two-dimensional quantum information processing and parallel search algorithms

Hadamard spectroscopy has earlier been used to speed-up multi-dimensional NMR experiments. In this work we speed-up the two-dimensional quantum computing scheme, by using Hadamard spectroscopy in the indirect dimension, resulting in a scheme which is faster and requires the Fourier transformation only in the direct dimension. Two and three qubit quantum gates are implemented with an extra observer qubit. We also use one-dimensional Hadamard spectroscopy for binary information storage by spatial encoding and implementation of a parallel search algorithm.Comment: 28 pages, 10 figures. Journal of Magnetic Resonance (In Press

Sociālie mediji radošām bibliotēkām

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Šahs Latvijas Universitātē

Gandrīz gadsimta laikā LU šahā izveidojušās daudzas spēcīgas personības: Vladimirs Petrovs, Marks Pasmans, Jānis Kļaviņš, Mihails Tāls, Jānis Klovāns, Aivars Gipslis, Benita Vilerte, Anda Šafranska, Agnese Sīpola, Rolands Bērziņš, Arturs Bernotas un daudzi citi

Thermal Equilibrium as an Initial State for Quantum Computation by NMR

We present a method of using a nuclear magnetic resonance computer to solve the Deutsch-Jozsa problem in which: (1) the number of molecules in the NMR sample is irrelevant to the number of qubits available to an NMR quantum computer, and (2) the initial state is chosen to be the state of thermal equilibrium, thereby avoiding the preparation of pseudopure states and the resulting exponential loss of signal as the number of qubits increases. The algorithm is described along with its experimental implementation using four active qubits. As expected, measured spectra demonstrate a clear distinction between constant and balanced functions.Comment: including 4 figure

The Fantastic Four: A plug 'n' play set of optimal control pulses for enhancing nmr spectroscopy

We present highly robust, optimal control-based shaped pulses designed to replace all 90{\deg} and 180{\deg} hard pulses in a given pulse sequence for improved performance. Special attention was devoted to ensuring that the pulses can be simply substituted in a one-to-one fashion for the original hard pulses without any additional modification of the existing sequence. The set of four pulses for each nucleus therefore consists of 90{\deg} and 180{\deg} point-to-point (PP) and universal rotation (UR) pulses of identical duration. These 1 ms pulses provide uniform performance over resonance offsets of 20 kHz (1H) and 35 kHz (13C) and tolerate reasonably large radio frequency (RF) inhomogeneity/miscalibration of (+/-)15% (1H) and (+/-)10% (13C), making them especially suitable for NMR of small-to-medium-sized molecules (for which relaxation effects during the pulse are negligible) at an accessible and widely utilized spectrometer field strength of 600 MHz. The experimental performance of conventional hard-pulse sequences is shown to be greatly improved by incorporating the new pulses, each set referred to as the Fantastic Four (Fanta4).Comment: 28 pages, 19 figure

MQD—Multiplex-Quadrature Detection in Multi-Dimensional NMR

With multiplex-quadrature detection (MQD) the tasks of coherence selection and quadrature separation in N-dimensional heteronuclear NMR experiments are merged. Thus the number of acquisitions required to achieve a desired resolution in the indirect dimensions is significantly reduced. The minimum number of transients per indirect data point, which have to be combined to give pure-phase spectra, is thus decreased by a factor (3/4)N−1. This reduction is achieved without adjustable parameters. We demonstrate the advantage by MQD 3D HNCO and HCCH-TOCSY spectra affording the same resolution and the same per-scan sensitivity as standard phase-cycled ones, but obtained in only 56 % of the usual time and by resolution improvements achieved in the same amount of time

Indirect detection of infinite-speed MAS solid-state NMR spectra

Heavy spin-1/2 nuclides are known to possess very large chemical shift anisotropies that can challenge even the most advanced magic-angle-spinning (MAS) techniques. Wide manifolds of overlapping spinning sidebands and insufficient excitation bandwidths often obfuscate meaningful spectral information and force the use of static, low-resolution solid-state (SS)NMR methods for the characterization of materials. To address these issues, we have merged fast-magic-angle-turning (MAT) and dipolar heteronuclear multiple-quantum coherence (D-HMQC) experiments to obtain D-HMQC-MAT pulse sequences which enable the rapid acquisition of 2D SSNMR spectra that correlate isotropic 1H chemical shifts to the indirectly detected isotropic “infinite-MAS” spectra of heavy spin-1/2 nuclides. For these nuclides, the combination of fast MAS and 1H detection provides a high sensitivity, which rivals the DNP-enhanced ultra-wideline SSNMR. The new pulse sequences were used to determine the Pt coordination environments in a complex mixture of decomposition products of transplatin and in a metal-organic framework with Pt ions coordinated to the linker ligands