4. The Qubit: Superposition

Superposition

Let's upgrade our analogy.

• Classical Bit: A coin flat on the table. It is definitely Heads OR Tails.
• Qubit: A coin spinning on the table. Is it Heads or Tails? It’s both and neither at the same time.

This state is called Superposition. The coin keeps spinning until you slap your hand down on it—this is measurement. Only then does it force itself to be Heads or Tails.

Interactive Task: Drag an H (Hadamard) gate to the circuit and run it. You'll see a 50/50 chance of measuring 0 or 1. Look at the Bloch Sphere below the results—the arrow points to the equator, representing the superposition state!