Abstract In this chapter, we familiarize ourselves with certain aspects of quantum weirdness, namely energy quantization, quantum tunneling, and quantum superposition. To this end, we consider three didactic examples of quantum systems, solve the respective scenario specific Schrödinger equations, and (mathematically and graphically) analyze and interpret the results we obtain therefrom. Despite of the utter simplicity of our scenarios, two of them already defy analytic solutions. Since this is not uncommon when trying to solve Schrödinger equations for specific settings, we also discuss simple numerical methods for Schrödinger equation solving and present code examples which implement those.
Abstract In this chapter, we familiarize ourselves with certain aspects of quantum weirdness, namely energy quantization, quantum tunneling, and quantum superposition. To this end, we consider three didactic examples of quantum systems, solve the respective scenario specific Schrödinger equations, and (mathematically and graphically) analyze and interpret the results we obtain therefrom. Despite of the utter simplicity of our scenarios, two of them already defy analytic solutions. Since this is not uncommon when trying to solve Schrödinger equations for specific settings, we also discuss simple numerical methods for Schrödinger equation solving and present code examples which implement those.
This chapter forms a capstone chapter for this book; in our discussion of complex numbers, we will be using principles we covered when exploring vectors (Chapter 6) and trigonometry (Chapter 5) and when considering exponential functions (Chapter 1). Additionally, we will be showing how a complex number can be treated in the same way as any other number, subject to one simple additional consideration. Despite their name, ‘complex’ numbers are not difficult to understand, and their use makes solving a range of chemical problems considerably more simple.
Chapter 2 begins with a discussion of the de Broglie wave concept that is the foundation of quantum mechanics. The idea that particles can exhibit wave-like behavior is an important part of the explanation of why atoms have discrete energy levels and make transitions in which electromagnetic radiation is absorbed or emitted at specific frequencies. Important aspects of how quantum systems may be observed and how they develop in time are presented. The Schrödinger equation is introduced and the importance of the wavefunction covered. Mathematical simplifications that arise from considering symmetry are covered. Several examples of simple quantum systems are presented in which the calculation of electronic energy structure based on boundary conditions is illustrated. Sections on wave–particle duality and quantum observables are followed by others on the dynamics of two-level systems, mathematically complete representations of arbitrary states, and standard approaches for handling the temporal development of wavefunctions.
In the first two chapters we have examined the basic principles – superposition (p. 18), complementarity (p. 19), quantization (p. 44), statistical algorithm (p. 57), and correspondence (p. 72) (see also Subsec. 2.3.4) – and the basic entities, observables and states, of quantum mechanics, as well as the main differences with respect to classical mechanics. While what we have discussed so far is rather a static picture of observables and states, in this chapter we shall deal with quantum dynamics, i.e. with the time evolution of quantum-mechanical systems. Historically, after Bohr had provided a quantized description of the atom (see Subsec. 1.5.4), Einstein showed the quantized nature of photons (see Subsec. 1.2.1), and de Broglie hypothized the wave-like nature of matter (see Subsec. 1.5.5), the first building block of quantum mechanics was provided by the commutation relations, proposed by Heisenberg in 1925, whose consequence is represented by the uncertainty relation (see Subsec. 2.2.7 and Sec. 2.3). This was the subject of the previous chapters. The dynamical part of the theory was proposed by Schrödinger in 1926, and is known as the Schrödinger equation. It is also known as wave mechanics (see Subsec. 1.5.7). In this chapter we shall show that Heisenberg's and Schrödinger's formulations are only two different aspects of the same theory. We shall also come back to this point in Sec. 8.1.1. Here, first we shall derive the fundamental equation which rules quantum dynamics (Sec. 3.1), and, in Sec. 3.2, we shall summarize the main properties of the Schrödinger equation.
Quantum mechanics allows a remarkably accurate description of nature and powerful predictive capabilities. The analyses of quantum systems and their interpretation lead to many surprises, for example, the ability to detect the characteristics of an object without ever touching it in any way, via "interaction-free measurement," or the teleportation of an atomic state over large distances. The results can become downright bizarre. Quantum mechanics is a subtle subject that usually involves complicated mathematics -- calculus, partial differential equations, etc., for complete understanding. Most texts for general audiences avoid all mathematics. The result is that the reader misses almost all deep understanding of the subject, much of which can be probed with just high-school level algebra and trigonometry. Thus, readers with that level of mathematics can learn so much more about this fundamental science. The book starts with a discussion of the basic physics of waves (an appendix reviews some necessary classical physics concepts) and then introduces the fundamentals of quantum mechanics, including the wave function, superposition, entanglement, Bell's theorem, etc., and applications to Bose--Einstein condensation, quantum computing, and much more. The interpretation of the mathematics of quantum mechanics into a world view has been the subject of much controversy. The result is a variety of conflicting interpretations, from the famous Copenhagen view of Bohr to the multiple universes of Everett. We discuss these interpretations in the chapter "What is a wave function?" and include some very recent advances, for example, quantum Bayesianism, and measurements of the reality of the wave function.
This article explores methodological aspects of teaching quantum mechanics in higher education within the framework of physics and mathematics programs. Particular attention is given to the challenge’s students face in mastering fundamental concepts due to the high level of abstraction inherent in the subject. The hydrogen atom model is considered as a focal example – being both conceptually significant and visually illustrative in demonstrating the principles of quantum theory. The core emphasis is placed on the interpretation of the wave function and its physical meaning through the concept of probability density. Methods for visualizing electron wave states are discussed, alongside graphical representations of probability densities corresponding to various quantum numbers. The relationship between the analytical solutions of the Schrodinger equation and the physical interpretation of these results is substantiated. Special attention is also devoted to developing students’ understanding of the probabilistic nature of quantum systems, as well as their ability to apply mathematical tools for modeling and interpreting quantum states. Didactic approaches are proposed to enhance students’ abstract thinking and intuitive grasp of quantum principles.
In the previous chapters, we have shown how to solve the Schrodinger equation for several systems as a particle in an infinite and finite potential well, scattering, harmonic oscillator, and hydrogen atom. For all these systems, we were able to solve Schrodinger's equation exactly. However, there are complicated potentials for which Schrodinger's equation cannot be solved exactly. For such situations, we resort to approximation methods for finding approximate solutions to the Schrodinger equation. In this chapter, we discuss several approximate methods for solving Schrodinger's equation.