Delta Potential Research Articles

Stationary scattering for the nonlinear Schrödinger equation with point-like obstacles: exact solutions

AbstractWe solve the Nonlinear Schrödinger Equation (NLSE) in 1D in presence of one, two and several Dirac delta potentials. With the help of an equivalent central force problem we obtain the analytical solutions in terms of a biparametric family containing the Jacobi functions. Elliptic Jacobi functions are already reported in the literature but they have not been used in the context of a scattering problem under causal boundary conditions. In the simplest examples of one or two Dirac deltas we analyze how the nonlinear term of the equation affects the modulus and phase profiles of the wave function. We also study the transmission curves under the nonlinear modification of the tunneling behavior for the first time. For a Fabri-Perot configuration made of two deltas, we obtain the effect of nonlinear coupling in the positions of the local maxima (resonances). We lay the foundations for nonlinear Anderson localization of 1D BECs in a speckle field. Upon redefinition of parameters these novel results describe the dynamics of a stationary Higgs field in 1D. Finally, we discuss the conditions for soliton formation under the influence of a Dirac comb potential, giving rise to fully correlated locations and intensities of the defects.

Piecewise linear potentials for false vacuum decay and negative modes

We study bounce solutions and associated negative modes in the class of piecewise linear triangular-shaped potentials that may be viewed as approximations of smooth potentials. In these simple potentials, the bounce solution and action can be obtained analytically for a general spacetime dimension D. The eigenequations for the fluctuations around the bounce are universal and have the form of a Schrödinger-like equation with delta-function potentials. This Schrödinger equation is solved exactly for the negative modes whose number is confirmed to be one. The latter result may justify the usefulness of such piecewise linear potentials in the study of false vacuum decay. Published by the American Physical Society 2024

Entanglement in Bound States of Two Particles with a Localized Center-of-Mass Wave-Function

Abstract We explore some entanglement-related features of systems consisting of two particles coupled through a central potential. We consider two types of systems, constituted by particles in one spatial dimension interacting through an attractive Dirac Delta potential, or through a harmonic quadratic potential. The degree of freedom corresponding to the system’s center of mass is either regarded as confined within a one dimensional box, or described by a localized Gaussian wave-packet. As a quantitative indicator of the degree of entanglement between the particles, we use the linear entropy of the one-particle marginal density matrix. In general, this quantity cannot be calculated analytically (except in some special cases related to the Harmonic interaction). Consequently, the linear entropy has to be evaluated numerically. Since the concomitant numerical problem consist in evaluating a multi-dimensional integral in four dimensions, the Monte Carlo integration method is an appropriate one for this task. We explore numerically how the system’s entanglement depends on the different interaction potentials, on the different types of confinement for the system’s center of mass, and on the associated parameters describing the size and geometry of the system.

Andreev bound states in Josephson junctions of semi-Dirac semimetals

We consider a Josephson junction built with the two-dimensional semi-Dirac semimetal, which features a hybrid of linear and quadratic dispersion around a nodal point. We model the weak link between the two superconducting regions by a Dirac delta potential because it mimics the thin-barrier-limit of a superconductor–barrier–superconductor configuration. Assuming a homogeneous pairing in each region, we set up the BdG formalism for electronlike and holelike quasiparticles propagating along the quadratic-in-momentum dispersion direction. This allows us to compute the discrete bound-state energy spectrum ɛ of the subgap Andreev states localized at the junction. In contrast with the Josephson effect investigated for propagation along linearly dispersing directions, we find a pair of doubly degenerate Andreev bound states. Using the dependence of ɛ on the superconducting phase difference ϕ, we compute the variation of Josephson current as a function of ϕ.

Revisiting the bound states of a confined delta potential

The stationary states of a particle under the influence of a delta potential confined by impenetrable walls are investigated using the method of expansion in orthogonal functions. The eigenfunctions of the time-independent Schrödinger equation are expressed in closed form by using a pair of closed-form expressions for series available in the literature. The analysis encompasses both attractive and repulsive potentials with arbitrary couplings. Confinement significantly impacts the quantum states and introduces a scenario of double degeneracy including the ground state. Analysis extends to discuss the transition to unconfinement. This research holds particular significance for educators and students engaged in mathematical methods applied to physics and quantum mechanics within undergraduate courses, offering valuable insights into the complex relationships among profiles of potentials, boundary conditions, and the resulting quantum phenomena.

The Solution of the Hierarchy of Quantum Kinetic Equations for Correlation Matrices with Delta function Potential

The Solution of the Hierarchy of Quantum Kinetic Equations for Correlation Matrices with Delta function Potential

On the normalization and density of 1D scattering states

The normalization of scattering states is more than a rote step necessary to calculate expectation values. This normalization actually contains important information regarding the density of the scattering spectrum (along with useful details on the bound states). For many applications, this information is more useful than the wavefunctions themselves. In this paper, we show that this correspondence between scattering state normalization and the density of states is a consequence of the completeness relation, and we present formulas for calculating the density of states, which are applicable to certain potentials. We then apply these formulas to the delta function potential and the square well. We then illustrate how the density of states can be used to calculate the partition function for a system of two particles with a point-like (delta potential) interaction.

Minimal Mass Blow-Up Solutions for the \(\boldsymbol{L}^{\boldsymbol{2}}\)-Critical NLS with the Delta Potential for Even Data in One Dimension

Minimal Mass Blow-Up Solutions for the \(\boldsymbol{L}^{\boldsymbol{2}}\)-Critical NLS with the Delta Potential for Even Data in One Dimension

Generalized One-Dimensional Periodic Potential Wells Tending to the Dirac Delta Potential

The solution of a quantum periodic potential in solid state physics is relevant because one can understand how electrons behave in a corresponding crystal. In this paper, the analytical solution of the energy formulation for a one-dimensional periodic potential that meets certain boundary conditions is developed in a didactic and detailed way. In turn, the group speed and effective mass are also calculated from the transcendental energy equation of a potential V=V(x). From this, a comparison is made with periodic potentials with known analytical solutions, such as the Dirac delta, as well as rectangular and triangular potentials. Finally, some limits are proposed in which these periodic potentials of the form V=V(x) approach the periodic Dirac delta potential of positive intensity. Therefore, the calculations described in this paper can be used as the basis for more-complex one-dimensional potentials and related simulations.

Threshold even solutions to the nonlinear Schrödinger equation with delta potential at high frequencies

Threshold even solutions to the nonlinear Schrödinger equation with delta potential at high frequencies

Renormalization in a wavelet basis

Discrete wavelet-based techniques hold the potential to establish a robust framework for the non-perturbative examination of quantum field theories. This study explores facets of renormalization within theories investigated through the wavelet-based framework. We showcase the non-perturbative application of regularization, renormalization, and the emergence of a flowing coupling constant within this framework. This is assessed using a model of a particle in an attractive 2-dimensional Dirac delta function potential in two spatial dimensions. This model is recognized for demonstrating fundamental features encountered in typical relativistic quantum field theories.

Accurate and efficient numerical methods for the nonlinear Schrödinger equation with Dirac delta potential

Accurate and efficient numerical methods for the nonlinear Schrödinger equation with Dirac delta potential

Finite time blowup for the nonlinear Schrödinger equation with a delta potential

Finite time blowup for the nonlinear Schrödinger equation with a delta potential

One-dimensional scattering of fermions in double Dirac delta potentials

The spectrum of bound and scattering states of the one dimensional Dirac Hamiltonian describing fermions distorted by a static background built from two Dirac delta potentials is studied. A distinction will be made between ‘mass-spike’ and ‘electrostatic’ δ-potentials. The second quantisation is then performed to promote the relativistic quantum mechanical problem to a relativistic quantum field theory and study the quantum vacuum interaction energy for fermions confined between opaque plates. The work presented here is a continuation of (Guilarte et al 2019 Front. Phys. 7 109).

Interaction of one-dimensional quantum droplets with potential wells and barriers

We address static and dynamical properties of one-dimensional (1D) quantum droplets (QDs) under the action of local potentials in the form of narrow wells and barriers. The dynamics of QDs is governed by the 1D Gross–Pitaevskii equation including the mean-field cubic repulsive term and the beyond-mean-field attractive quadratic one. In the case of the well represented by the delta-function potential, three exact stable solutions are found for localized states pinned to the well. The Thomas–Fermi approximation for the well and the adiabatic approximation for the collision of the QD with the barrier are developed too. Collisions of incident QDs with the wells and barriers are analyzed in detail by means of systematic simulations. Outcomes, such as fission of the moving QD into transmitted, reflected, and trapped fragments, are identified in relevant parameter planes. In particular, a counter-intuitive effect of partial or full rebound of the incident QD from the potential well is studied in detail and qualitatively explained.

Infrared effects and the Unruh state

Detailed behaviors of the modes of quantized scalar fields in the Unruh state for various eternal black holes in two dimensions are investigated. It is shown that the late-time behaviors of some of the modes of the quantum fields and of the symmetric two-point function are determined by infrared effects. The nature of these effects depends upon whether there is an effective potential in the mode equation and what form this potential takes. Here, three cases are considered, one with no potential and two with potentials that are nonnegative everywhere and are zero on the event horizon of the black hole and zero at either infinity or the cosmological horizon. Specifically, the potentials are a delta function potential and the potential that occurs for a massive scalar field in Schwarzschild–de Sitter spacetime. In both cases, scattering effects remove infrared divergences in the mode functions that would otherwise arise from the normalization process. When such infrared divergences are removed, it is found that the modes that are positive frequency with respect to the Kruskal time on the past black hole horizon approach zero in the limit that the radial coordinate is fixed and the time coordinate goes to infinity. In contrast, when there is no potential and thus infrared divergences occur, the same modes approach nonzero constant values in the late-time limit when the radial coordinate is held fixed. The behavior of the symmetric two-point function when the field is in the Unruh state is investigated for the case of a delta function potential in certain asymptotically flat black hole spacetimes in two dimensions. The removal of the infrared divergences in the mode functions results in the elimination of terms that grow linearly in time.

Polar magneto-optic Kerr and Faraday effects in finite periodic PT -symmetric systems

We discuss the anomalous behavior of the Faraday (transmission) and polar Kerr (reflection) rotation angles of the propagating light, in finite periodic parity-time ($\mathcal{P}\mathcal{T}$) symmetric structures, consisting of $N$ cells. The unit cell potential is two complex $\delta$-potentials placed on both boundaries of the ordinary dielectric slab. It is shown that, for a given set of parameters describing the system, a phase transition-like anomalous behavior of Faraday and Kerr rotation angles in a parity-time symmetric systems can take place. In the anomalous phase the value of one of the Faraday and Kerr rotation angles can become negative, and both angles suffer from spectral singularities and give a strong enhancement near the singularities. We also shown that the real part of the complex angle of KR, $\theta^{R}_1$, is always equal to the $\theta^{T}_1$ of FR, no matter what phase the system is in due to the symmetry constraints. The imaginary part of KR angles $\theta^{R^{r/l}}_2$ are related to the $\theta^{T}_2$ of FR by parity-time symmetry. Calculations based on the approach of the generalized nonperturbative characteristic determinant, which is valid for a layered system with randomly distributed delta potentials, show that the Faraday and Kerr rotation spectrum in such structures has several resonant peaks. Some of them coincide with transmission peaks, providing simultaneous large Faraday and Kerr rotations enhanced by an order one or two of magnitude. We provide a recipe for funding a one-to-one relation in between KR and FR.

Electrodeposition of bimetal Ni-Co oxide as a bifunctional electrocatalyst for rechargeable zinc air battery

Zinc air battery is a promising candidate green energy storage due to its high energy density and low-cost. However, most of the preparation of air cathode in the literature involves a lengthy and inefficient process of mixing catalyst powders with a polymeric binder. Herein, we synthesize bimetal Ni-Co oxide through a simple electrodeposition technique followed by annealing at a low temperature under atmospheric conditions. The addition of cobalt at various contents significantly alters surface morphology from tiny nanoparticles to a 2D nano-sheet structure. The performance of the as-prepared catalysts were firstly evaluated toward the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in alkaline solution. Our results show that the incorporating cobalt in the NiO host structure not only improve the OER but also the ORR activities. The required potential to drive OER at a current density of 10 mA/cm2 and the half-wave potential for ORR using the NC-2 catalyst are 1.567 and 0.855 V vs. RHE, respectively, resulting a delta potential of 0.712 V. Furthermore, we demonstrate the practical application of the NC-2 catalyst as the air cathode electrode for assembling a liquid zinc air battery device. The battery test reveals that NC-2 has an open circuit potential of 1.36 V and a specific capacity of 714 mAh/gZn with an excellent stability performance for about 80 h. Our findings suggest that bimetal Ni-Co oxide is a promising catalyst for enhancing the performance of zinc air batteries.

Response of Electrical Networks with Delta Potential via Mohand Transform

Response of Electrical Networks with Delta Potential via Mohand Transform

Renormalization in a wavelet basis

Discrete wavelet-based methods promise to emerge as an excellent framework for the non-perturbative analysis of quantum field theories. In this work, we investigate aspects of renormalization in theories analyzed using wavelet-based methods. We demonstrate the nonperturbative approach of regularization, renormalization, and the emergence of flowing coupling constant within the context of these methods. This is tested on a model of the particle in an attractive Dirac delta function potential in two spatial dimensions, which is known to demonstrate quintessential features found in a typical relativistic quantum field theory.