F. M. Toyama

Accurate numerical solutions of the time-dependent Schrödinger equation

We present a generalization of the often-used Crank-Nicolson (CN) method of obtaining numerical solutions of the time-dependent Schrödinger equation. The generalization yields numerical solutions accurate to order (Deltax)2r-1 in space and (Deltat)2M in time for any positive integers r and M, while CN employ r=M=1. We note dramatic improvement in the attainable precision (circa ten or greater orders of magnitude) along with several orders of magnitude reduction of computational time. The improved method is shown to lead to feasible studies of coherent-state oscillations with additional short-range interactions, wave-packet scattering, and long-time studies of decaying systems.

General aspects of the bound‐state solutions of the one‐dimensional Dirac equation

Two theorems regarding the bound‐state solutions of the one‐dimensional Dirac equation are verified: A—There is no degeneracy of energy; B—When the potential is a Lorentz scalar and the potential is continuously varied, the energy does not cross zero. Some features of the Dirac equation related to these theorems are discussed.

The Fermi pseudo-potential in one dimension

Wu and Yu recently examined point interactions in one dimension in the form of the Fermi pseudo-potential. On the other hand there are point interactions in the form of self-adjoint extensions (SAEs) of the kinetic energy operator. We examine the relationship between the point interactions in these two forms in the one-channel and two-channel cases. In the one-channel case the pseudo-potential leads to the standard three-parameter family of SAEs. In the two-channel case the pseudo-potential furnishes a ten-parameter family of SAEs.

Energy-dependent point interactions in one dimension

We consider a new type of point interaction in one-dimensional quantum mechanics. It is characterized by a boundary condition at the origin that involves the second and/or higher order derivatives of the wavefunction. The interaction is effectively energy dependent. It leads to a unitary S-matrix for the transmission–reflection problem. The energy dependence of the interaction can be chosen such that any given unitary S-matrix (or the transmission and reflection coefficients) can be reproduced at all energies. Generalization of the results to coupled-channel cases is discussed.

The Time-Dependent Schrödinger Equation : The Need for the Hamiltonian to be Self-Adjoint

We present some simple arguments to show that quantum mechanics operators are required to be self-adjoint. We emphasize that the very definition of a self-adjoint operator includes the prescription of a certain domain of the operator. We then use these concepts to revisit the solutions of the time-dependent Schroedinger equation of some well-known simple problems ‐ the infinite square well, the finite square well, and the harmonic oscillator. We show that these elementary illustrations can be enriched by using more general boundary conditions, which are still compatible with self-adjointness. In particular, we show that a puzzling problem associated with the Hydrogen atom in one dimension can be clarified by applying the correct requirements of self-adjointness.

Bohmian description of a decaying quantum system

We present a Bohmian description of a decaying quantum system. A particle is initially confined in a region around the origin which is surrounded by a repulsive potential barrier. The particle leaks out in time tunneling through the barrier. We determine Bohm trajectories with which we can visualize various features of the decaying system.

Multiphase matching in the Grover algorithm

Phase matching has been studied for the Grover algorithm as a way of enhancing the efficiency of the quantum search. Recently Li and Li found that a particular form of phase matching yields, with a single Grover operation, a success probability greater than

Stability of two-electron bound states in a model quantum wire☆

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Reaction of the nonlinear Dirac equation to a nonlinear Schrodinger equation with a correction term

for finding the equal-amplitude superposition of marked states when the fraction of the marked states stored in a database state is greater than

Logarithmic perturbation expansion for the Dirac equation in one dimension: Application to the polarizability calculation

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