291 research outputs found
Implementable Quantum Bit-String Commitment Protocol
Quantum bit-string commitment[A.Kent, Phys.Rev.Lett., 90, 237901 (2003)] or
QBSC is a variant of bit commitment (BC). In this paper, we propose a new QBSC
protocol that can be implemented using currently available technology, and
prove its security under the same security criteria as discussed by Kent. QBSC
is a generalization of BC, but has slightly weaker requirements, and our
proposed protocol is not intended to break the no-go theorem of quantum BC.Comment: To appear in Phys. Rev. A., 9 pages, 2 figure
Insights into the mechanism for gold catalysis: behaviour of gold(i) amide complexes in solution
We report the synthesis and activity of new mononuclear and dinuclear gold amide complexes . The dinuclear complexes and were characterised by single crystal X-ray analysis. We also report solution NMR and freezing point depression experiments to rationalise their behaviour in solution and question the de-ligation process invoked in gold catalysis
Heisenberg exchange parameters of molecular magnets from the high-temperature susceptibility expansion
We provide exact analytical expressions for the magnetic susceptibility
function in the high temperature expansion for finite Heisenberg spin systems
with an arbitrary coupling matrix, arbitrary single-spin quantum number, and
arbitrary number of spins. The results can be used to determine unknown
exchange parameters from zero-field magnetic susceptibility measurements
without diagonalizing the system Hamiltonian. We demonstrate the possibility of
reconstructing the exchange parameters from simulated data for two specific
model systems. We examine the accuracy and stability of the proposed method.Comment: 13 pages, 7 figures, submitted to Phys. Rev.
Properties of low-lying states in some high-nuclearity Mn, Fe and V clusters: Exact studies of Heisenberg models
Using an efficient numerical scheme that exploits spatial symmetries and spin
parity, we have obtained the exact low-lying eigenstates of exchange
Hamiltonians for the high nuclearity spin clusters, Mn_{12}, Fe_8 and V_{15}.
The largest calculation involves the Mn_{12} cluster which spans a Fock space
of a hundred million. Our results show that the earlier estimates of the
exchange constants need to be revised for the Mn_{12} cluster to explain the
level ordering of low-lying eigenstates. In the case of the Fe_8 cluster,
correct level ordering can be obtained which is consistent with the exchange
constants for the already known clusters with butterfly structure. In the
V_{15} cluster, we obtain an effective Hamiltonian that reproduces exactly, the
eight low-lying eigenvalues of the full Hamiltonian.Comment: Revtex, 12 pages, 16 eps figures; this is the final published versio
High frequency resonant experiments in Fe molecular clusters
Precise resonant experiments on Fe magnetic clusters have been
conducted down to 1.2 K at various tranverse magnetic fields, using a
cylindrical resonator cavity with 40 different frequencies between 37 GHz and
110 GHz. All the observed resonances for both single crystal and oriented
powder, have been fitted by the eigenstates of the hamiltonian . We have identified the
resonances corresponding to the coherent quantum oscillations for different
orientations of spin S = 10.Comment: to appear in Phys.Rev. B (August 2000
Uniform bounds on complexity and transfer of global properties of Nash functions
We show that the complexity of semialgebraic sets and mappings can be used to parametrize Nash sets and mappings by Nash families. From this we deduce uniform bounds on the complexity of Nash functions that lead to first-order descriptions of many properties of Nash functions and a good behaviour under real closed field extension (e.g. primary decomposition). As a distinguished application, we derive the solution of the extension and global equations problems over arbitrary real closed fields, in particular over the field of real algebraic numbers. This last fact and a technique of change of base are used to prove that the Artin-Mazur description holds for abstract Nash functions on the real spectrum of any commutative ring, and solve extension and global equations in that abstract setting. To complete the view, we prove the idempotency of the real spectrum and an abstract version of the separation problem. We also discuss the conditions for the rings of abstract Nash functions to be noetherian
Characterization of the S = 9 excited state in Fe8Br8 by Electron Paramagnetic Resonance
High Frequency electron paramagnetic resonance has been used to observe the
magnetic dipole, M = 1, transitions in the excited
state of the single molecule magnet FeBr. A Boltzmann analysis of the
measured intensities locates it at 24 2 K above the ground
state, while the line positions yield its magnetic parameters D = -0.27 K, E =
0.05 K, and B = -1.3 10 K. D is thus smaller by 8%
and E larger by 7% than for . The anisotropy barrier for is
estimated as 22 K,which is 25% smaller than that for (29 K). These
data also help assign the spin exchange constants(J's) and thus provide a basis
for improved electronic structure calculations of FeBr.Comment: 7 pages, Figs included in text, submitted to PR
Magnetic Anisotropy in the Molecular Complex V15
We apply degenerate perturbation theory to investigate the effects of
magnetic anisotropy in the magnetic molecule V15. Magnetic anisotropy is
introduced via Dzyaloshinskii-Moriya (DM) interaction in the full Hilbert space
of the system. Our model provides an explanation for the rounding of
transitions in the magnetization as a function of applied field at low
temperature, from which an estimate for the DM interaction is found. We find
that the calculated energy differences of the lowest energy states are
consistent with the available data. Our model also offers a novel explanation
for the hysteretic nature of the time-dependent magnetization data.Comment: Final versio
Nuclear spin-lattice relaxation in ferrimagnetic clusters and chains: A contrast between zero and one dimensions
Motivated by ferrimagnetic oligonuclear and chain compounds synthesized by
Caneschi et al., both of which consist of alternating manganese(II) ions and
nitronyl-nitroxide radicals, we calculate the nuclear spin-lattice relaxation
rate 1/T_1 employing a recently developed modified spin-wave theory. 1/T_1 as a
function of temperature drastically varies with the location of probe nuclei in
both clusters and chains, though the relaxation time scale is much larger in
zero dimension than in one dimension. 1/T_1 as a function of an applied field
in long chains forms a striking contrast to that in finite clusters, diverging
with decreasing field like inverse square root at low temperatures and
logarithmically at high temperatures.Comment: to be published in Phys. Rev. B 68 August 01 (2003
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