Showing papers on "Ladder operator published in 2007"

Factorization method in quantum mechanics

Abstract: PART I - Introduction. 1: Introduction. 1.1 Basic review. 1.2. Motivations and aims. PART II - Method. 2: Theory. 2.1. Introduction. 2.2. Formalism. 3: Lie Algebras SU(2) and SU(1,1). 3.1. Introduction. 3.2. Abstract groups. 3.3. Matrix representation. 3.4. properties of groups SU(2) and SO(3). 3.5. Properties of non-compact groups SO(2,1) and SU(1,1). 3.6. Generators of Lie groups SU(2) and SU(1,1). 3.7. Irreducible representations. 3.8. Irreducible unitary representations. 3.9. Concluding remarks. PART III - Applications in Non-Relativistic Quantum mechanics. 4: Harmonic Oscillator. 4.1. Introduction. 4.2. Exact solutions. 4.3. Ladder operators. 4.4. Bargmann-Segal transformations. 4.5. Single mode realization of dynamic group SU(1,1). 4.6. Matrix elements. 4.7. Coherent states. 4.8. Franck-Condon factors. 4.9. Concluding remarks. 5: Infinitely Deep Square-Well Potential. 5.1. Introduction. 5.2. Ladder operators for infinitely deep square-well potential. 5.3. Realization of dynamic group SU(1,1) and matrix elements. 5.4. Ladder operators for infinitely deep symmetric well potential. 5.5. SUSYQM approach to infinitely deep square-well potential. 5.6. Perelomov coherent states. 5.7. Barut-Girardello coherent states. 5.8. Concluding remarks. 6: Morse Potential. 6.1. Introduction. 6.2. Exact solutions. 6.3. Ladder operators for the Morse potential. 6.4. Realization of dynamic group SU(2). 6.5. Matrix elements. 6.6. Harmonic limit. 6.7. Franck-Condon factors. 6.8. Transition probability. 6.9. Realization of dynamic group SU(1,1). 6.10. Concluding remarks. 7: Poschl-Teller Potential. 7.1. Introduction. 7.2. Exact solutions. 7.3. Ladder operators. 7.4. Realization of dynamic group SU(2). 7.5. Alternative approach to derive ladder operators. 7.6. Harmonic limit. 7.7. Expansions of the coordinate x and momentum p from the SU(2) generators.7.8. Concluding remarks. 8: Pseudoharmonic Oscillator. 8.1. Introduction. 8.2. Exact solutions in one dimension. 8.3. Ladder operators. 8.4. Barut-Girardello coherent states. 8.5. Thermodynamic properties. 8.6. Pseudoharmonic oscillator in arbitrary dimensions. 8.7. Recurrence relations among matrix elements. 8.8. Concluding remarks. 9: Algebraic Approach to an Electron in a Uniform Magnetic Field. 9.1. Introduction. 9.2. Exact solutions. 9.3. Ladder operators. 9.4. Concluding remarks. 10: Ring-Shaped Non-Spherical Oscillator. 10.1. Introduction. 10.2. Exact solutions. 10.3. Ladder operators. 10.4. Realization of dynamic group. 10.5. Concluding remarks. 11: Generalized Laguerre Functions. 11.1. Introduction. 11.2. generalized Laguerre functions. 11.3. Ladder operators and realization of dynamic group SU(1,1). 11.4. Concluding remarks. 12: New Non-Central Ring-Shaped Potential. 12.1. Introduction. 12.2. Bound states. 12.3. Ladder operators. 12.4. Mean values. 12.5. Continuum states. 12.6. Concluding remarks. 13: Poschl-Teller Like Potential. 13.1. Introduction. 13.2. Exact solutions. 13.3. Ladder operators. 13.4. Realization of dynamic group and matrix elements. 13.5. Infinitely square-well and harmonic limits. 13.6. Concluding remarks. 14: Position-Dependent Mass Schrodinger Equation for a Singular Oscillator. 14.1. Introduction. 14.2. Position-dependent effective mass Schrodinger equation for harmonic oscillator. 14.3. Singular oscillator with a position-dependent effective mass. 14.4. Complete solutions. 14.5. Another position-dependent effective mass. 14.6. Concluding remarks. PART IV - Applications in Relativistic Quantum Mechanics. 15: SUSYQM and SKWB Approach to the Dirac Equation with a Coulomb Potential in 2+1 Dimensions. 15.1. Introduction. 15.2. Dirac equation in 2+1 dimensions. 15.3. Exact solutions. 15.4. SUSYQM

Algebraic approach to the Kratzer potential

Abstract: In this paper, the energy eigenvalues and the corresponding eigenfunctions are calculated for the Kratzer potential. Then we obtain the ladder operators for the one-dimensional (1D) and 3D Kratzer potential. Finally, we show that these operators satisfy the SU(2) commutation relation.

Hidden symmetries and thermodynamic properties for a harmonic oscillator plus an inverse square potential

Abstract: The exact solutions of a one-dimensional Schrodinger equation with a harmonic oscillator plus an inverse square potential are obtained. The ladder operators constructed directly from the normalized wavefunctions are found to satisfy a su(1, 1) algebra. Another hidden symmetry is used to explore the relations between the eigenvalues and eigenfunctions by substituting x −ix. The vibrational partition function Z is calculated exactly to study thermodynamic functions such as the vibrational mean energy U, specific heat C, free energy F, and entropy S. It is both interesting and surprising to find that both vibrational specific heat C and entropy S are independent of the potential strength α. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

Quantum brachistochrone problem and the geometry of the state space in pseudo-hermitian quantum mechanics

Abstract: A non-Hermitian operator with a real spectrum and a complete set of eigenvectors may serve as the Hamiltonian operator for a unitary quantum system provided that one makes an appropriate choice for the defining the inner product of physical Hilbert state. We study the consequences of such a choice for the representation of states in terms of projection operators and the geometry of the state space. This allows for a careful treatment of the quantum Brachistochrone problem and shows that it is indeed impossible to achieve faster unitary evolutions using PT-symmetric or other non-Hermitian Hamiltonians than those given by Hermitian Hamiltonians.

Modes of a twisted optical cavity

Abstract: An astigmatic optical resonator consists of two astigmatic mirrors facing each other. The resonator is twisted when the symmetry axes of the mirrors are nonparallel. We present an algebraic method to obtain the complete set of the paraxial eigenmodes of such a resonator. Basic ingredients are the complex eigenvectors of the four-dimensional transfer matrix that describes the transformation of a ray of light over a roundtrip of the resonator. The relation between the fundamental mode and the higher-order modes is expressed in terms of raising operators in the spirit of the ladder operators of the quantum harmonic oscillator.

On the Spectrum of the Weighted p-Biharmonic Operator with Weight

Abstract: In this work we give a non decreasing sequence of positive eigenvalues of the weighted p-biharmonic operator with weight and with Navier boundary conditions, then we study the simplicity and the isolation of the first positive eigenvalue. Finally, we study the one dimensional case.

Quantization and conformal properties of a generalized Calogero model

Abstract: We analyze a generalization of the quantum Calogero model with the underlying conformal symmetry, paying special attention to the two-body model deformation. Owing to the underlying SU(1,1) symmetry, we find that the analytic solutions of this model can be described within the scope of the Bargmann representation analysis, and we investigate its dynamical structure by constructing the corresponding Fock space realization. The analysis from the standpoint of supersymmetric quantum mechanics (SUSYQM), when applied to this problem, reveals that the model is also shape invariant. For a certain range of the system parameters, the two-body generalization of the Calogero model is shown to admit a one-parameter family of self-adjoint extensions, leading to inequivalent quantizations of the system.

Disappearing Q operator

Abstract: In the Schroedinger formulation of non-Hermitian quantum theories a positive-definite metric operator {eta}{identical_to}e{sup -Q} must be introduced in order to ensure their probabilistic interpretation. This operator also gives an equivalent Hermitian theory, by means of a similarity transformation. If, however, quantum mechanics is formulated in terms of functional integrals, we show that the Q operator makes only a subliminal appearance and is not needed for the calculation of expectation values. Instead, the relation to the Hermitian theory is encoded via the external source j(t). These points are illustrated and amplified for two non-Hermitian quantum theories: the Swanson model, a non-Hermitian transform of the simple harmonic oscillator, and the wrong-sign quartic oscillator, which has been shown to be equivalent to a conventional asymmetric quartic oscillator.

An operator-theoretic approach to invariant integrals on quantum homogeneous SU n,1 -spaces

Abstract: An operator-theoretic approach to invariant integrals on non-compact quantum spaces is introduced on the examples of quantum ball algebras. In order to describe an invariant integral, operator algebras are associated to the quantum space which allow an interpretation as "rapidly decreasing" functions and as functions with compact support. If an operator representation of a first order differential calculus over the quantum space is known, then it can be extended to the operator algebras of integrable functions. The important feature of the approach is that these operator algebras are topological spaces in a natural way. For suitable representations and with respect to the bounded and weak operator topologies, it is shown that the algebra of functions with compact support is dense in the algebra of closeable operators used to define these algebras of functions and that the infinitesimal action of the quantum symmetry group is continuous.

A simple and efficient evolution operator for time-dependent Hamiltonians: the Taylor expansion.

Abstract: No compact expression of the evolution operator is known when the Hamiltonian operator is time dependent, like when Hamiltonian operators describe, in a semiclassical limit, the interaction of a molecule with an electric field. It is well known that Magnus N. Magnus, Commun. Pure Appl. Math. 7, 649 1954 has derived a formal expression where the evolution operator is expressed as an exponential of an operator defined as a series. In spite of its formal simplicity, it turns out to be difficult to use at high orders. For numerical purposes, approximate methods such as “Runge-Kutta” or “split operator” are often used usually, however, to a small order 5, so that only small time steps, about one-tenth or one-hundredth of the field cycle, are acceptable. Moreover, concerning the latter method, split operator, it is only very efficient when a diagonal representation of the kinetic energy operator is known. The Taylor expansion of the evolution operator or the wave function about the initial time provides an alternative approach, which is very simple to implement and, unlike split operator, without restrictions on the Hamiltonian. In addition, relatively large time steps up to the field cycle can be used. A two-level model and a propagation of a Gaussian wave packet in a harmonic potential illustrate the efficiency of the Taylor expansion. Finally, the calculation of the time-averaged absorbed energy in fluoroproprene provides a realistic application of our method. © 2007 American Institute of Physics.

Eigenfunctions and eigenvalues of the Dougherty collision operator

Abstract: The Dougherty collision operator is a simplified Fokker-Planck collision operator that conserves particle number, momentum, and energy. In this paper, a complete set of orthogonal eigenfunctions of the linearized Dougherty operator is obtained. Five of the eigenfunctions have zero eigenvalue and correspond to the five conserved quantities (particle number, three components of momentum, and energy). The connection between the eigenfunctions and fluid modes in the limit of strong collisionality is demonstrated; in particular, the sound speed, thermal conductivity, and viscosity predicted by the Dougherty operator are identified.

Symmetry and stochastic gene regulation.

Abstract: Lorentz-like noncompact Lie symmetry SO(2,1) is found in a spin-boson stochastic model for gene expression. The invariant of the algebra characterizes the switch decay to equilibrium. The azimuthal eigenvalue describes the affinity between the regulatory protein and the gene operator site. Raising and lowering operators are constructed and their actions increase or decrease the affinity parameter. The classification of the noise regime of the gene arises from the group theoretical numbers.

Factorizing the time evolution operator

Abstract: There is a widespread belief in the quantum physical community, and textbooks used to teach quantum mechanics, that it is a difficult task to apply the time evolution operator on an initial wavefunction. Because the Hamiltonian operator is, generally, the sum of two operators, then it is not possible to apply the time evolution operator on an initial wavefunction ψ(x, 0), for it implies using terms like . A possible solution is to factorize the time evolution operator and then apply successively the individual exponential operator on the initial wavefunction. However, the exponential operator does not directly factorize, i.e. . In this study we present a useful procedure for factorizing the time evolution operator when the argument of the exponential is a sum of two operators, which obey specific commutation relations. Then, we apply the exponential operator as an evolution operator for the case of elementary unidimensional potentials, like a particle subject to a constant force and a harmonic oscillator. Also, we discuss an apparent paradox concerning the time evolution operator and non-spreading wave packets addressed previously in the literature.

Algebraic Approach to the Hulthen Potential

Abstract: In this paper the energy eigenvalues and the corresponding eigenfunctions are calculated for Hulthen potential Then we obtain the ladder operators and show that these operators satisfy SU(2) commutation relation

Some properties of Stark states of hydrogenic atoms and ions

Abstract: The motivation for this work is the problem of providing accurate values of the atomic transition matrix elements for the Stark components of Rydberg–Rydberg transitions in atomic hydrogen and hydrogenic ions, for use in spectral line broadening calculations applicable to cool, low-density plasmas, such as those found in H II regions. Since conventional methods of calculating these transition matrix elements cannot be used for the high principal quantum numbers now easily attained in radio astronomical spectra, we attempt to show that the recurrence relation (ladder operator) method recently employed by Watson (2006 J. Phys. B: At. Mol. Opt. Phys. 39 1889–97) and Hey (2006 J. Phys. B: At. Mol. Opt. Phys. 39 2641–64) can be taken over into the parabolic coordinate system used to describe the Stark states of the atomic (ionic) radiators. The present method is therefore suggested as potentially useful for extending the work of Griem (1967 Astrophys. J. 148 547–58, 2005 Astrophys. J. 620 L133–4), Watson (2006), Stambulchik et al (2007 Phys. Rev. E 75 016401(9 pp) on Stark broadening in transitions between states of high principal quantum number, to physical conditions where the binary, impact approximation is no longer strictly applicable to both electron and ion perturbers. Another possible field of application is the study of Stark mixing transitions in 'ultracold' Rydberg atoms perturbed by long-range interactions with slow atoms and ions. Preparatory to the derivation of recurrence relations for states of different principal quantum number, a number of properties and recurrence relations are also found for states of identical principal quantum number, including the analogue in parabolic coordinates to the relations of Pasternack (1937 Proc. Natl Acad. Sci. USA 23 91–4, 250) in spherical polar coordinates.

An Indefinite Convection-Diffusion Operator

Abstract: We give a mathematically rigorous analysis which confirms the surprising results in a recent paper of Benilov, O'Brien and Sazonov about the spectrum of a highly singular non-self-adjoint operator that arises in a problem in fluid mechanics.

Univalent harmonic functions

Abstract: Harmonic functions, Dziok-Srivastava operator, Convolution, Integral operator, Distortion bounds, Neighborhood. Abstract: A necessary and sufficient coefficient is given for functions in a class of complex- valued harmonic univalent functions using the Dziok-Srivastava operator. Dis- tortion bounds, extreme points, an integral operator, and a neighborhood of such functions are considered.

(p,q) deformations and (p,q)-vector coherent states of the Jaynes-Cummings model in the rotating wave approximation

Abstract: Classes of (p,q) deformations of the Jaynes-Cummings model in the rotating wave approximation are considered. Diagonalization of the Hamiltonian is performed exactly, leading to useful spectral decompositions of a series of relevant operators. The latter include ladder operators acting between adjacent energy eigenstates within two separate infinite discrete towers, except for a singleton state. These ladder operators allow for the construction of (p,q)-deformed vector coherent states. Using (p,q) arithmetics, explicit and exact solutions to the associated moment problem are displayed, providing new classes of coherent states for such models. Finally, in the limit of decoupled spin sectors, our analysis translates into (p,q) deformations of the supersymmetric harmonic oscillator, such that the two supersymmetric sectors get intertwined through the action of the ladder operators as well as in the associated coherent states.

The HVZ Theorem for a Pseudo-Relativistic Operator

Abstract: The localization of the essential spectrum of a relativistic two-electron ion is provided. The analysis is performed with the help of the pseudo-relativistic Brown–Ravenhall operator which is the restriction of the Coulomb–Dirac operator to the electrons’ positive spectral subspace.

Canonical and nonlinear vector coherent states of generalized models with spin-orbit interaction

Abstract: Through canonical and f deformation quantizations, classes of nonlinear spin-orbit interaction models are considered. These generalized models are relevant in condensed matter physics and quantum optics in domains of nonlinear spin-Hall effect or of the multiphoton Jaynes-Cummings [Proc. IEEE 51, 89 (1963)] model, for instance. A spectral decomposition follows the exact diagonalization of the Hamiltonian and leads to the definition of ladder operators acting on the associated Hilbert space. Nonlinear vector coherent states are then constructed from a general lowering operator action. Explicit solutions of their related moment problems in ordinary and f-deformed theories are displayed, thus providing new classes of coherent states for such generalized spin-orbit models.

Some developments in vertex operator algebra theory, old and new

Abstract: In this exposition, I discuss several developments in the theory of vertex operator algebras, and I include motivation for the definition.

Heisenberg operators, invariant domains and heisenberg equations of motion

Abstract: An abstract operator theory is developed on operators of the form AH(t) := eitHAe-itH, t ∈ ℝ, with H a self-adjoint operator and A a linear operator on a Hilbert space (in the context of quantum mechanics, AH(t) is called the Heisenberg operator of A with respect to H). The following aspects are discussed: (i) integral equations for AH(t) for a general class of A; (ii) a sufficient condition for D(A), the domain of A, to be left invariant by e-itH for all t ∈ ℝ; (iii) a mathematically rigorous formulation of the Heisenberg equation of motion in quantum mechanics and the uniqueness of its solutions; (iv) invariant domains in the case where H is an abstract version of Schrodinger and Dirac operators; (v) applications to Schrodinger operators with matrix-valued potentials and Dirac operators.

Projection operator techniques and Hilbert space averaging in the quantum theory of nonequilibrium systems

Abstract: The development of efficient strategies for the treatment of the dynamics of relevant observables in complex quantum systems plays a decisive role in the theory of quantum relaxation and transport behavior. Here we discuss the most important tools that are based on the projection operator techniques of nonequilibrium statistical mechanics. For both the Nakajima-Zwanzig and the time-convolutionless projection operator technique we derive the equations of motion for a set of relevant observables and develop explicit expressions in second and fourth order of the corresponding perturbation expansions. We also discuss the Hilbert space average method which is based on the idea of a best guess of conditional quantum expectations determined by an average over a suitable region in the underlying Hilbert space, and relate this method to the projection operator technique.

Raising and Lowering of Generalized Hulthén Potential from Supersymmetry Approaches

Abstract: We obtain the exact bound states of the generalized of Hulthen potential with negative energy levels using an analytic approach. In order to obtain bound states, we use the associated Jacobi differential equation. Using the supersymmetry approach to quantum mechanics, we show that these bound states, via four pairs of first order differential operators, represent four types of ladder equations. Two types of these supersymmetric structures suggest derivation of algebric solutions for the bound states using two different approaches.

Algebraic approach to radial ladder operators in the hydrogen atom

Abstract: We add a phase variable and its corresponding operator to the description of the hydrogen atom. With the help of these additions, we device operators that act as ladder operators for the radial system. The algebra defined by the commutation relations between those operators has a Casimir operator coincident with the radial Hamiltonian of the problem. The algebra happens to be the well-known su(1,1) Lie algebra, hence the phase-dependent eigenfunctions calculated within our scheme belong in a representation of that algebra, a fact that may be useful in certain applications. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem 107: 1608–1613, 2007

Spectrum of the Kerzman-Stein Operator for the Ellipse

Abstract: The skew-hermitian part of the Cauchy operator, defined with respect to arclength measure on the boundary, is known as the Kerzman-Stein operator. For an ellipse, the eigenvalues of this operator are shown to have multiplicity two. For an ellipse with small eccentricity, we compute the leading coefficient in the asymptotic expansion of the eigenvalues.

Bernoulli, Euler, permutations and quantum algebras

Abstract: The combinatorial properties of the Bernoulli and Euler numbers are interpreted using a new classification of permutations. The classification is naturally described by an operator algebra of a type familiar from quantum theory. It has a duality structure described by an operator satisfying anticommutation relations.