289 research outputs found
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
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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
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