Contents

# Contents

## Idea

In quantum theory the state of a physical system is given by a vector in a complex vector space (usually a Hilbert space). This means that given any two states $\psi_1$ and $\psi_2$, also their sum as vectors $\psi_1 + \psi_2$ is represents a state. This is called the quantum superposition of the two states.

Since/if these quantum states are thought of as wavefunctions solving linear differential equations such as the Schroedinger equation, Dirac equation, Klein-Gordon equation or Tomonaga-Schwinger equation, their quantum superposition is an example of the general principle of superposition of solutions to linear differential equations.

The concept of quantum superposition is at the heart of what makes quantum physics peculiar, notably via the phenomenon of entanglement.