The Qubit

Superposition and measurement

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• A qubit is $\alpha|0\rangle + \beta|1\rangle$, with $|\alpha|^2 + |\beta|^2 = 1$.
• Measurement gives 0 or 1 with probabilities equal to the squared amplitudes.
• Amplitudes can be negative; signs don’t change probabilities directly.

Steps

1. More than a bit
2. Measuring
3. The qubit circle
4. Measuring many copies
5. Amplitudes for ten qubits
6. Measure twice