A qubit’s values between 0 and 1
A bit’s value is either 0 or 1. In contrast, a qubit’s value can be |0⟩, |1⟩, or anything in between |0⟩ and |1⟩. But that’s not the whole story. Imagine a qubit that (in some way or other) is halfway between |0⟩ and |1⟩. This qubit has infinitely many different ways of being between |0⟩ and |1⟩. To understand this infinite number of ways, we need some visual aids.
Pictorially, each bit is on one of two points. Figure 2.1 shows these points:
Figure 2.1 – A bit’s value is either 0 or 1
In contrast, we can think of a qubit as being somewhere on the surface of a sphere. We call it a Bloch sphere. Here are some facts about the Bloch sphere:
- A qubit on the Bloch sphere’s north pole has a value of |0⟩. Figure 2.2 shows this sphere:
Figure 2.2 – A |0⟩ qubit
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