Chapter 1 Introduction

One normally makes a distinction between quantum mechanics and quantum physics. Quantum physics is concerned with those processes that involve discrete energies, and quanta (such as photons). Quantum Mechanics concerns the study of a speciﬁc part of quantum physics, those quantum phenomena described by Schrödinger’s equation.

Quantum physics plays a rôle on small (atomic and subatomic) scales (say length scales of the order of $1{0}^{-9}m$) and below. You can see whether an expression has a quantum-physical origin as soon as it contains Planck’s constant in one of its two guises

$\begin{array}{rcll}h& =& 6.626\cdot 1{0}^{-34}Js,& \text{}\\ \hslash & =& h∕2\pi =1.055\cdot 1{0}^{-34}Js.& \text{(1.1)}\text{}\text{}\end{array}$

Here we shall shortly review some of the standard examples for the break-down classical physics, which can be described by introducing quantum principles.