Some remarks on discrete aperiodic Schrödinger operators

We consider Schrödinger operators onl ²( ) with deterministic aperiodic potential and Schrödinger operators on the l²-space of the set of vertices of Penrose tilings and other aperiodic self-similar tilings. The operators onl ²( ) fit into the formalism of ergodic random Schrödinger operators. Hence, their Lyapunov exponent, integrated density of states, and spectrum are almost-surely constant. We show that they are actually constant: the Lyapunov exponent for one-dimensional Schrödinger operators with potential defined by a primitive substitution, the integrated density of states, and the spectrum in arbitrary dimension if the system is strictly ergodic. We give examples of strictly ergodic Schrödinger operators that include several kinds of almost-periodic operators that have been studied in the literature. For Schrödinger operators on Penrose tilings we prove that the integrated density of states exists and is independent of boundary conditions and the particular Penrose tiling under consideration.     

Inverse spectral problem for the 2-sphere Schrödinger operators with zonal potentials

Two basic problems of spectral theory of Schrödinger operators H=–+V(x) on the 2-sphere S ₂ are studied: (Direct problem) calculate large-k asymptotics of eigenvalue clusters {_kj}_j in terms of the potential function V; (Inverse problem) recover V from asymptotics of eigenvalue clusters. We get an explicit solution of the inverse problem and establish local spectral rigidity for zonal potentials V.The research was partly supported by the US NSF Grant DMS-8620231 and the Case Research Initiation Grant.     

Spectral Theory of Herglotz Functions and Their Compositions

Recent developments in the theory of value distribution for boundary values of Herglotz functions [5], with applications to the spectral analysis of Herglotz measures and differential operators [2, 3] lead in a natural way to the investigation of measures which relate (through the Herglotz representation theorem) to the composition of a pair of Herglotz functions F,G. The present paper provides results on the boundary values of composed Herglotz functions and on the terms of their Herglotz representation which are dominant at large |z|.     

Spectral stability under tunneling

We study the spectral properties of multiple well Schrödinger operators on ⁿ . We give in particular upper bounds on energy shifts due to tunnel effect and localization properties of wave packets. Our methods are based on Agmon type estimates for resolvents in classically forbidden regions and geometric perturbation theory. Our results are valid also for an infinite number of wells, arbitrary spectral type and in non-semi-classical regimes.Laboratoire Propre, Centre National de la Recherche ScientifiquePhymat, Université de Toulon et du Var     

Appearance of a purely singular continuous spectrum in a class of random schrödinger operators

We consider a discrete Schrödinger operator on l²() with a random potential decaying at infinity as ¦n¦^–1/2. We prove that its spectrum is purely singular. Together with previous results, this provides simple examples of random Schrödinger operators having a singular continuous component in its spectrum.     

The final states in photoemission and field emission

For a semiinfinite medium and for a slab it is shown how the final state functions describing photoemission and field emission are to be defined if more than one solution of the Schrödinger equation for a fixed value of the energyE and the parallel componentk of the wave vectork exist. As by-product some interesting statements concerning complexband structure and the solutions of the Schrödinger equation for a semiinfinite medium or a crystalline slab are derived.     

Low energy asymptotics for Schrödinger operators with slowly decreasing potentials

Low energy behavior of Schrödinger operators with potentials which decay slowly at infinity is studied. It is shown that if the potential is positive then the zero energy is very regular and the resolvent is smooth near 0. This implies rapid local decay for the solutions of the Schrödinger equation. On the other hand, if the potential is negative then the resolvent has discontinuity at zero energy. Thus one cannot expect local decay faster than ordert ^–1 ast.     

Anderson localization for multi-dimensional systems at large disorder or large energy

We prove that discrete Schrödinger operators on ^d with a random-potential have almost-surely only pure point spectrum and exponentially decaying eigenfunctions for large disorder or large energy. This is the first proof of localization for multi-dimensional Anderson models.Groupe de recherche 048 du CNRS     

On the spectral problem for anyons

We consider the spectral problem resulting from the Schrödinger equation for a quantum system ofn2 indistinguishable, spinless, hard-core particles on a domain in two dimensional Euclidian space. For particles obeying fractional statistics, and interacting via a repulsive hard core potential, we provide a rigorous framework for analysing the spectral problem with its multi-valued wave functions.Partially supported by the Mathematical Sciences Research Institute, Berkeley California, under NSF Grant # DMS 8505550Partially supported under NSF Grant no. DMR-9101542     

On the Essential Spectrum of Two-Dimensional Periodic Magnetic Schrödinger Operators

For two-dimensional Schrödinger operators with a nonzero constant magnetic field perturbed by an infinite number of periodically disposed, long-range magnetic and electric wells, it is proven that when the inter-well distance (R) grows to infinity, the essential spectrum near the eigenvalues of the one well Hamiltonian is located in mini-bands whose widths shrink faster than any exponential with R. This should be compared with our previous result, which stated that, in the case of compactly supported wells, the mini-bands shrink Gaussian-like with R.     

Physical foundations of quantum theory: Stochastic formulation and proposed experimental test

The time-dependent Schrödinger equation has been derived from three assumptions within the domain of classical and stochastic mechanics. The continuity equation isnot used in deriving the basic equations of the stochastic theory as in the literature. They are obtained by representing Newton's second law in a time-inversion consistent equation. Integrating the latter, we obtain the stochastic Hamilton-Jacobi equation. The Schrödinger equation is a result of a transformation of the Hamilton-Jacobi equation and linearization by assigning the arbitrary constant =2mD. An experiment is proposed to determine and to test a hypothesis of the theory directly. A mathematical apparatus is formulated from the Jacobian formalism to derive physical parameters from (x, t) and to obtain operators for the boundary cases of the theory. The operator formalisms are compared by means of a well-known solution in the quantum theory.     

A generalized spectral duality theorem

We establish a version of the spectral duality theorem relating the point spectrum of a family of^*-representations of a certain covariance algebra to the continuous spectrum of an associated family of^*-representations. Using that version, we prove that almost all the images of any element of a certain space of fixed points of some^*-automorphism of an irrational rotation algebra via standard^*-representations of the algebra inl ² do not have pure point spectrum over any non-empty open subset of the common spectrum of those images. As another application of the spectral duality theorem, we prove that if almost all the Bloch operators associated with a real almost periodic function on have pure point spectrum over a Borel subset of , then almost all the Schrödinger operators with potentials belonging to the compact hull of the translates of this function have, over the same set, purely continuous spectrum.Dedicated to Professor Marek Burnat     

Real Spectra of PT-symmetric Operators and Perturbation Theory

A criterion is provided for the reality of the spectrum for a class of non self-adjoint operators in a Hilbert space invarariant under a particular discrete symmetry. Applications to the PT-symmetric Schrödinger operators are discussed.     

A remark on Schrödinger operators on aperiodic tilings

We prove that for a large class of Schrödinger operators on aperiodic tilings the spectrum and the integrated density of states are the same for all tilings in the local isomorphism class, i.e., for all tilings in the orbit closure of one of the tilings. This generalizes the argument in earlier work from discrete strictly ergodic operators onl ²( ^d ) to operators on thel ²-spaces of sets of vertices of strictly ergodic tilings.     

su q (2)-invariant harmonic oscillator

We propose a q-deformation of the su(2)-invariant Schrödinger equation of a spinless particle in a central potential, which allows us not only to determine a deformed spectrum and the corresponding eigenstates, as in other approaches, but also to calculate the expectation values of some physically-relevant operators. Here we consider the case of the isotropic harmonic oscillator and of the quadrupole operator governing its interaction with an external field. We obtain the spectrum and wave functions both for q R⁺ and generic q S ¹, and study the effects of the q-value range and of the arbitrariness in the su _q (2) Casimir operator choice. We then show that the quadrupole operator in l = 0 states provides a good measure of the deformation influence on the wave functions and on the Hilbert space spanned by them.     

Localization in general one-dimensional random systems

We discuss two ways of extending the recent ideas of localization from discrete Schrödinger operators (Jacobi matrices) to the continuum case. One case allows us to prove localization in the Goldshade, Molchanov, Pastur model for a larger class of functions than previously. The other method studies the model –+V, whereV is a random constant in each (hyper-) cube. We extend Wegner's result on the Lipschitz nature of the ids to this model.Dedicated to Walter Thirring on his 60^th birthdayResearch partially supported by USNSF under Grant DMS-8416049     

Relations between the wave solutions and the jost solutions off the energy shell for local central potentials

Using the Green function techniques we express the wave solutions of the radial inhomogeneous Schrödinger equation by means of the on-shell Jost and regular solutions. Making use of their boundary behaviour atr = andr = 0 we reexpress them alternatively in terms of the off-shell Jost and regular solutions. Relations among the different generalized (fully off the energy shell) Jost functions are derived and the radial matrix elements of the transition and reaction (reactance) operators are given in terms of these Jost functions. The relations reflect the principle of detailed balance.     

The one-dimensional Schrödinger equation and a periodic potential

After recalling basic facts from the Titchmarsh-Weyl theory we derive and investigate the linear matrix equation, which holds for functions related to the spectral matrix of the one-dimensional periodic Schrödinger equation. The Weyl's solutions of the Schrödinger equation are used, when we solve this equation and associated nonlinear equations of the Milne's type. Two distinct trace formulae reconstructing the potential follow simply from the transformed and modified Milne's equations. Necessary spectral data of the inverse problem are determined by an infinite system of nonlinear first-order ordinary differential equations. Nonuniqueness of the solution of the inverse problem is confirmed on the other hand by writing a broad variety of the isospectral Darboux transformations.     

Green Functions of the Stationary Schrödinger Equation and Tomographic Representation of Quantum Mechanics

Invertible maps of operators of quantum observables onto functions of c-number arguments and their associative products are reviewed. In particular, the symplectic tomography map is discussed and an expression connecting an arbitrary operator and its tomographic symbol is written down. This formula is applied to obtain explicit expressions for tomographic symbols, which are symplectic tomograms of Green functions of stationary and nonstationary Schrödinger equations written for the case of harmonic oscillator. The connection between the so-called classical propagator (X,,,t,X,,,0) and the tomographic symbol of the evolution operator of nonstationary Schrödinger equation is found. The spin tomography is presented as a map of operators acting in spinor space onto functions of c-arguments. As an example, the spin located in a magnetic field is considered and the tomographic symbol of resolventa is obtained. Tomographic symbols of hermitian conjugate operators are shown to be complex conjugate functions.