Summary

In this chapter, we developed the tools to describe a qubit. We changed a qubit’s state by sending the qubit through a quantum gate. In mathematical terms, the gate applies an operator to the qubit – an operator that we represent using a matrix.

In classical computing, things start to become interesting when we execute statements conditionally. Most languages have if statements for conditional execution. To perform conditional execution at the quantum level, we need some kind of qubit-to-qubit interaction. One qubit changes if some other qubit’s state is |1⟩.

To achieve this interaction, we need some new operators. Each such operator acts on more than one qubit at a time. We use matrices to represent these operators. When we do, we discover some bizarre effects. That’s what the next chapter is all about.