Quantum Computing Algorithms

2

What Is a Qubit?

“A qubit is a quantum bit.” That’s a nice soundbite, but what does it mean? In this chapter, we’ll do our best to answer that question.

To describe a qubit, we’ll start with a rough analogy. We’ll rely on some very informal (maybe even heretical) terminology and work our way to a more precise description.

Our description will take several forms. We’ll start by drawing a sharp distinction between qubits and classical bits. We’ll assert that a qubit’s value isn’t necessarily 0 or 1. Instead, a qubit’s value can be a number (of some kind) that’s between 0 and 1. To make this assertion more believable, we’ll explain how to implement qubits in a laboratory using elementary particles such as electrons and photons.

A bit can sit ...