Quantum mechanics is the theory that describes dynamics of small objects such as atom and molecule. In this paper, Schrodinger’s wave mechanics, a part of quantum mechanics, is studied. The central equation of this wave mechanics is the Schrodinger’s equation. Solving this equation, quantum system dynamics can be described. In this work, the quantum scattering problem in one dimension is studied. Wave functions are obtained by exactly solving the Schrodinger’s equation in case of the delta function potential and the rectangular potential. The transmission and reflection probabilities are calculated from the obtained wave functions. Lower bounds on the transmission probabilities are presented. Finally, the lower bounds on the transmission probabilities are applied to the delta function potential and the rectangular potential problems. The results show that the exact transmission probabilities satisfy the lower bounds on the transmission probabilities.
Quantum mechanics is the theory that describes dynamics of small objects such as atom and molecule. In this paper, Schrodinger’s wave mechanics, a part of quantum mechanics, is studied. The central equation of this wave mechanics is the Schrodinger’s equation. Solving this equation, quantum system dynamics can be described. In this work, the quantum scattering problem in one dimension is studied. Wave functions are obtained by exactly solving the Schrodinger’s equation in case of the delta function potential and the rectangular potential. The transmission and reflection probabilities are calculated from the obtained wave functions. Lower bounds on the transmission probabilities are presented. Finally, the lower bounds on the transmission probabilities are applied to the delta function potential and the rectangular potential problems. The results show that the exact transmission probabilities satisfy the lower bounds on the transmission probabilities.
Quantum mechanics is a theory that can explain phenomena of atom-sized matter or smaller, which classical mechanics cannot do. The central equation of quantum mechanics is the Schrödinger equation. Mathematically, the Schrödinger equation is a second order partial differential equation which tells us how a wave function changes with time. For most problems in quantum mechanics, the Schrödinger equation cannot present exact solutions, except for a few idealized systems in which the Schrödinger equation can be solved exactly. Therefore, approximation methods are needed to find solutions to the Schrödinger equation. In this paper, systems in stationary states are of special interest, in which the Schrödinger equation is reduced to the time-independent Schrödinger equation. One of the approximation methods that work for systems in stationary states is the WKB approximation. In this paper, transmission probabilities for various potentials are calculated using the WKB approximation. The potentials studied in this paper are composed of the asymmetric square-well potential, the hyperbolic tangent potential, the squared hyperbolic secant potential, and the double squared hyperbolic secant potential.
The Schrödinger equation is a fundamental equation in physics for describing quantum mechanical behavior. It is a partial differential equation that shows how a wave function of a physical system evolves over time. In addition, it is associated with the kinetic energy and the potential energy, both of which contribute towards the total energy. This paper explains mathematical aspect of the Schrödinger equation. The concept of the WKB approximation has also been reviewed, which is an important method in finding the approximate solutions for the wave function. In addition, the paper also shows how to derive the transmission and reflection probabilities in relation to a one-dimensional quantum problem, called a “tunneling problem”, which occurs when a classical particle passes through a region where total energy is less than its potential energy. The WKB approximation can be used as a basis for formally writing down the exact solutions. Furthermore, it gives a high accuracy for the propagation of waves with high frequency or short wavelength.
The Schrödinger equation assumes that a particle behaves as a wave and yields a solution in terms of wave function and the energy of the particle under consideration. Once the wave function is known, then everything about the particle can be deduced from the wave function. This chapter covers the development of the Schrödinger wave equation and its applications to one-dimensional systems. Time-dependent and time-independent Schrödinger equations, bound and scattering states, probability density, probability current and expectation values, the solution of the time-independent 1D-Schrödinger equation for a free particle, infinite as well as finite potential wells, potential steps, and the finite potential barrier are discussed in detail in the chapter. The phenomenon of tunneling, relevance and the importance of the free particle, potential wells and potential barriers to contemporary fields of physics and chemistry, periodic solids and their band structures, the Kronig-Penney model, confined states in quantum wells, and wires and dots are other topics presented in innovative manners in the chapter. The importance of the topics presented here is demonstrated through carefully chosen solved examples and unsolved exercises from contemporary fields of sciences.
It is shown that in the case of the one-particle one-dimensional scattering problem for a given time-independent potential, for each state of the whole quantum ensemble of identically prepared particles, there is an unique pair of (subensemble's) solutions to the Schrödinger equation, which, as we postulate, describe separately transmission and reflection: in the case of nonstationary states, for any instant of time, these functions are orthogonal and their sum describes the state of all particles; evolving with constant norms, one of them approaches at late times the transmitted wave packet and another approaches the reflected packet. Both for transmission and reflection, 1) well before and after the scattering event, the average kinetic energy of particles is the same, 2) the average starting point differs, in the general case, from that for all particles. It is shown that for reflection, in the case of symmetric potential barriers, the domain of the motion of particles is bounded by the midpoint of the barrier region. We define (exact and asymptotic) transmission and reflection times and show that the basic results of our formalism can be, in principle, checked experimentally.
A propagator for the one dimensional time-dependent Schrödinger equation with an asymmetric rectangular potential is obtained using the multiple-scattering theory approach. It allows for the consideration of the reflection and transmission processes as the particle scattering at the potential jump (in contrast to the conventional wave-like picture) and for accounting for the nonclassical counterintuitive contribution of the backward-moving component of the wave packet attributed to the particle. This propagator completely resolves the corresponding time-dependent Schrödinger equation (defines the wave function ψ(x,t)) and allows for considering the quantum mechanical effects of a particle reflection from the potential downward step/well and a particle tunneling through the potential barrier as a function of time. These results are related to fundamental issues such as measuring time in quantum mechanics (tunneling time, time of arrival, dwell time). For imaginary time, which represents an inverse temperature (t→−iℏ/kBT), the obtained propagator is equivalent to the density matrix for a particle that is in a heat bath and is subject to a rectangular potential. If one shifts to imaginary time (t→−it), the matrix element of the calculated propagator in the spatial basis provides a solution to the diffusion-like equation with a rectangular potential. The obtained exact results are presented as the integrals from elementary functions and thus allow for a numerical visualization of the probability density ∣ψ(x,t)∣2, the density matrix and the solution of the diffusion-like equation. The results obtained may also be useful for spintronics applications due to the fact that the asymmetric (spin-dependent) rectangular potential can model the potential profile in layered magnetic nanostructures.