The Metallacyclopentane-Olefin Interchange Reaction

Tris(triphenylphosphine)tetramethylenenickel(II) and biscyclopentadienyltetramethylenetitanium, prepared from the reaction of a 1,4-dilithiobutane and the transition metal dihalides react with olefins to produce substituted metallacyclopentanes; the stereochemistry and substitution pattern of the metallocycles formed from propene, octa-1,7-diene, and norbornadiene has been determined

Deceptive Apparent Nonadiabatic Magnetization Process

We discuss the effect of the thermal environment on the low-temperature response of the magnetization of uniaxial magnets to a time-dependent applied magnetic field. At sufficiently low temperatures the staircase magnetization curves observed in molecular magnets such as Mn_{12} and Fe_8 display little temperature dependence. However the changes of the magnetization at each step do not seem to be directly related to the probability for a quantum mechanical nonadiabatic transition. In order to explain this deceptive apparent nonadiabatic behavior, we study the quantum dynamics of the system in a thermal environment and propose a relation between the observed magnetization steps and the quantum mechanical transition probability due to the nonadiabatic transition.Comment: 4 pages, 7 eps figure

Quantum Annealing in the Transverse Ising Model

We introduce quantum fluctuations into the simulated annealing process of optimization problems, aiming at faster convergence to the optimal state. Quantum fluctuations cause transitions between states and thus play the same role as thermal fluctuations in the conventional approach. The idea is tested by the transverse Ising model, in which the transverse field is a function of time similar to the temperature in the conventional method. The goal is to find the ground state of the diagonal part of the Hamiltonian with high accuracy as quickly as possible. We have solved the time-dependent Schr\"odinger equation numerically for small size systems with various exchange interactions. Comparison with the results of the corresponding classical (thermal) method reveals that the quantum annealing leads to the ground state with much larger probability in almost all cases if we use the same annealing schedule.Comment: 15 pages, RevTeX, 8 figure

Quantum Spin Dynamics and Quantum Computation

We describe a simulation method for a quantum spin model of a generic, general purpose quantum computer. The use of this quantum computer simulator is illustrated through several implementations of Grover's database search algorithm. Some preliminary results on the stability of quantum algorithms are presented.Comment: 6 pages, 4 figures ; Minor errors corrected and figures update

Half-magnetization plateau stabilized by structural distortion in the antiferromagnetic Heisenberg model on a pyrochlore lattice

Magnetization plateaus, visible as anomalies in magnetic susceptibility at low temperatures, are one of the hallmarks of frustrated magnetism. We show how an extremely robust half-magnetization plateau can arise from coupling between spin and lattice degrees of freedom in a pyrochlore antiferromagnet, and develop a detailed symmetry of analysis of the simplest possible scenario for such a plateau state. The application of this theory to the spinel oxides CdCr2O4 and HgCr2O4, where a robust half magnetization plateau has been observed, is discussed.Comment: 4 pages, 4 figure

Quantum Fluctuation-Induced Phase Transition in S=1/2 XY-like Heisenberg Antiferromagnets on the Triangular Lattice

The selection of the ground state among nearly degenerate states due to quantum fluctuations is studied for the S=1/2 XY-like Heisenberg antiferromagnets on the triangular lattice in the magnetic field applied along the hard axis, which was first pointed out by Nikuni and Shiba. We find that the selected ground state sensitively depends on the degree of the anisotropy and the magnitude of the magnetic field. This dependence is similar to that in the corresponding classical model at finite temperatures where various types of field induced phases appear due to the entropy effect. It is also found that the similarity of the selected states in the classical and quantum models are not the case in a two-leg ladder lattice, although the lattice consists of triangles locally and the ground state of this lattice in the classical case is the same as that of the triangular lattice.Comment: 15 pages, 35 figure