249 research outputs found
The multiple quantum NMR dynamics in systems of equivalent spins with the dipolar ordered initial state
The multiple quantum (MQ) NMR dynamics in the system of equivalent spins with
the dipolar ordered initial state is considered. The high symmetry of the MQ
Hamiltonian is used in order to develop the analytical and numerical methods
for an investigation of the MQ NMR dynamics in the systems consisting of
hundreds of spins from "the first principles". We obtain the dependence of the
intensities of the MQ NMR coherences on their orders (profiles of the MQ NMR
coherences) for the systems of spins. It is shown that these
profiles may be well approximated by the exponential distribution functions. We
also compare the MQ NMR dynamics in the systems of equivalent spins having two
different initial states, namely the dipolar ordered state and the thermal
equilibrium state in the strong external magnetic field.Comment: 11 pages 4 figure
Multiple Quantum NMR Dynamics in Dipolar Ordered Spin Systems
We investigate analytically and numerically the Multiple Quantum (MQ) NMR
dynamics in systems of nuclear spins 1/2 coupled by the dipole-dipole
interactions in the case of the dipolar ordered initial state. We suggest two
different methods of MQ NMR. One of them is based on the measurement of the
dipolar temperature in the quasi-equilibrium state which establishes after the
time of order T2 after the MQ NMR experiment. The other method uses an
additional resonance 45^0 -pulse after the preparation period of the standard
MQ NMR experiment in solids. Many-spin clusters and correlations are created
faster in such experiments than in the usual MQ NMR experiments and can be used
for the investigation of many-spin dynamics of nuclear spins in solids.Comment: 11 pages, 3 figures. accepted for publication in Physical Review
Relationship between probabilities of the state transfers and entanglements in spin systems with simple geometrical configurations
In this paper we derive analytical relations between probabilities of the
excited state transfers and entanglements calculated by both the Wootters and
positive partial transpose (PPT) criteria for the arbitrary spin system with
single excited spin in the external magnetic field and Hamiltonian commuting
with . We apply these relations to study the arbitrary state transfers and
entanglements in the simple systems of nuclear spins having two- and
three-dimensional geometrical configurations with Hamiltonian. It is
shown that High-Probability State Transfers (HPSTs) are possible among all four
nodes placed in the corners of the rectangle with the proper ratio of sides as
well as among all eight nodes placed in the corners of the parallelepiped with
the proper ratio of sides. Entanglements responsible for these HPSTs have been
identified.Comment: 27pages, 10 figure
Exact results on spin dynamics and multiple quantum dynamics in alternating spin-1/2 chains with XY-Hamiltonian at high temperatures
We extend the picture of a transfer of nuclear spin-1/2 polarization along a
homogeneous one-dimensional chain with the XY-Hamiltonian to the inhomogeneous
chain with alternating nearest neighbour couplings and alternating Larmor
frequencies. To this end, we calculate exactly the spectrum of the spin-1/2
XY-Hamiltonian of the alternating chain with an odd number of sites. The exact
spectrum of the XY-Hamiltonian is also applied to study the multiple quantum
(MQ) NMR dynamics of the alternating spin-1/2 chain. MQ NMR spectra are shown
to have the MQ coherences of zero and second orders just as in the case
of a homogeneous chain. The intensities of the MQ coherences are calculated.Comment: 10 pages, 4 figure
Multiple quantum NMR of spin-carrying molecules in nanopores: high order corrections to the two-spin/two-quantum Hamiltonian
This paper is devoted to the multiple-quantum (MQ) NMR spectroscopy in
nanopores filled by a gas of spin-carrying molecules (s=1/2) in a strong
external magnetic field. It turned out that the high symmetry of the spin
system in nanopores yields a possibility to overcome the problem of the
exponential growth of the Hilbert space dimension with an increase in the
number of spins and to investigate MQ NMR dynamics in systems consisting of
several hundred spins. We investigate the dependence of the MQ coherence
intensities on their order (the profile of the MQ coherence intensities) for a
spin system governed by the standard MQ NMR Hamiltonian (the nonsecular
two-quantum/two-spin Hamiltonian) together with the second order correction of
the average Hamiltonian theory. It is shown that the profile depends on the
value of this correction and varies from the exponential to the logarithmic
one.Comment: 7 pages, 3 figure
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