Searcharxiv⌕ Search

arXiv subjects

Takashi Ichinose

Publications and source records attributed to Takashi Ichinose.

13 recordsLinked to original sources
arXiv2020

Note on a Product Formula Related to Quantum Zeno Dynamics

Given a nonnegative self-adjoint operator $H$ acting on a separable Hilbert space and an orthogonal projection $P$ such that $H_P := (H^{1/2}P)^*(H^{1/2}P)$ is densely defined, we prove that $\lim_{n\rightarrow \infty} (P\,\mathrm{e}^{-itH/n}P)^n = \mathrm{e}^{-itH_P}P$ holds in the strong operator topology. We also derive modifications of this product formula and its extension to the situation when $P$ is replaced by a strongly continuous projection-valued function satisfying $P(0)=P$.

math-ph↗
arXiv2017

Kato's Inequality for Magnetic Relativistic Schrödinger Operators

Kato's inequality is shown for the magnetic relativistic Schrödinger operator $H_{A,m}$ defined as the operator theoretical {\it square root} of the selfadjoint, magnetic nonrelativistic Schrödinger operator $(-i\nabla-A(x))^2+m^2$ with an $L^{2}_{\text{\rm loc}}$ vector potential $A(x)$.

math.AP↗
arXiv2016

On Three Imaginary-time Path Integral Formulas with Magnetic Fields in Relativistic Quantum Mechanics

Three magnetic relativistic Schrödinger operators are considered, corresponding to the classical relativistic Hamiltonian symbol with both magnetic vector and electric scalar potentials. Path integral representations for the solutions of their respective imaginary-time relativistic Schrödinger equations, i.e. heat equations are given in two ways. The one is by means of the probability path space measure coming from the Lévy process concerned, and the other is through time-sliced approximation with Chernoff's theorem.

math-ph↗
arXiv2014

Improved Sobolev Embedding Theorems for Vector-valued Functions

The aim of this paper is to give an extension of the improved Sobolev embedding theorem for single-valued functions to the case of vector-valued functions which is involved with the three-dimensional massless Dirac operator together with the three- or two-dimensional Weyl--Dirac (or Pauli) operator, the Cauchy--Riemann operator and also the four-dimensional Euclidian Dirac operator.

math-ph↗
arXiv2014

Magnetic Relativistic Schrödinger Operators and \\Imaginary-time Path Integrals

Three magnetic relativistic Schrödinger operators corresponding to the classical relativistic Hamiltonian symbol with magnetic vector and electric scalar potentials are considered, dependent on how to quantize the kinetic energy term $\sqrt{(ξ-A(x))^2 +m^2}$. We discuss their difference in general and their coincidence in the case of constant magnetic fields, and also study whether they are covariant under gauge transformation. Then results are reviewed on path integral representations for their respective imaginary-time relativistic Schrödinger equations, i.e. heat equations, by means of the probability path space measure related to the Lévy process concerned.

math-ph↗
arXiv2012

Probabilistic Representation and Fall-Off of Bound States of Relativistic Schrödinger Operators with Spin 1/2

A Feynman-Kac type formula of relativistic Schrödinger operators with unbounded vector potential and spin 1/2 is given in terms of a three-component process consisting of Brownian motion, a Poisson process and a subordinator. This formula is obtained for unbounded magnetic fields and magnetic field with zeros. From this formula an energy comparison inequality is derived. Spatial decay of bound states is established separately for growing and decaying potentials by using martingale methods.

math-ph↗
arXiv2010

Path Integral Representation for Schroedinger Operators with Bernstein Functions of the Laplacian

Path integral representations for generalized Schrödinger operators obtained under a class of Bernstein functions of the Laplacian are established. The one-to-one correspondence of Bernstein functions with Lévy subordinators is used, thereby the role of Brownian motion entering the standard Feynman-Kac formula is taken here by subordinated Brownian motion. As specific examples, fractional and relativistic Schrödinger operators with magnetic field and spin are covered. Results on self-adjointness of these operators are obtained under conditions allowing for singular magnetic fields and singular external potentials as well as arbitrary integer and half-integer spin values. This approach also allows to propose a notion of generalized Kato class for which hypercontractivity of the associated generalized Schrödinger semigroup is shown. As a consequence, diamagnetic and energy comparison inequalities are also derived.

math-ph↗
arXiv2010

Dirac--Sobolev Spaces and Sobolev Spaces

The aim of this work is to study the first order Dirac-Sobolev spaces in $L^p$ norm on an open subset of ${\mathbb R}^3$ to clarify its relationship with the corresponding Sobolev spaces. It is shown that for $1< p <\infty$, they coincide, while for $p=1$, the latter spaces are proper subspaces of the former.

math.AP↗
arXiv2006

Zeno product formula revisited

We introduce a new product formula which combines an orthogonal projection with a complex function of a non-negative operator. Under certain assumptions on the complex function the strong convergence of the product formula is shown. Under more restrictive assumptions even operator-norm convergence is verified. The mentioned formula can be used to describe Zeno dynamics in the situation when the usual non-decay measurement is replaced by a particular generalized observables in the sense of Davies.

math-ph↗
arXiv2005

On relations between stable and Zeno dynamics in a leaky graph decay model

We use a caricature model of a system consisting of a quantum wire and a finite number of quantum dots, to discuss relation between the Zeno dynamics and the stable one which governs time evolution of the dot states in the absence of the wire. We analyze the weak coupling case and argue that the two time evolutions can differ significantly only at times comparable with the lifetime of the unstable system undisturbed by perpetual measurement.

quant-ph↗
arXiv2000

Geometrically induced spectrum in curved leaky wires

We study measure perturbations of the Laplacian in $L^2(\R^2)$ supported by an infinite curve $Γ$ in the plane which is asymptotically straight in a suitable sense. We show that if $Γ$ is not a straight line, such a ``leaky quantum wire'' has at least one bound state below the threshold of the essential spectrum.

math-ph↗