An Invitation to Algebraic Methods in Quantum Theory

Abstract

In this paper, we present various well-studied examples of quantum systems, and discuss how they might be analysed algebraically. We analyse the harmonic oscillator, hydrogenic atom, optical components, and particle spin using multiple algebraic methods, and highlight the central importance of algebraic relationships between operators in determining the physical character of the system. In particular, we show: the ubiquity of the Lie algebra $\mathfrak{so}(2,1)\cong\mathfrak{su}(1,1)$ as the ``spectrum generating algebra''; the role of $\mathfrak{su}(2)$ and $\mathfrak{su}(1,1)$ in determining the action of optical components; that an elementary algebraic approach to particle spin offers novel insights into its nature versus the usual approaches; and how understanding the full (often hidden) symmetry of a problem enables it to be solved immediately without the need to solve differential equations. We hope this work will serve as a gentle introduction to algebraic methods in quantum mechanics for the interested reader --- we therefore signpost active areas of research within the community.