Beginner10 min read
Interference: Where the Power Comes From
Not "it tries every answer at once" — but "it arranges for the wrong answers to cancel".
Before this: Superposition & Measurement
In this lesson you’ll learn
- Show that applying H twice returns |0⟩ exactly, and explain why no coin can do that
- Trace how negative amplitudes cancel to make an outcome impossible
- Recognise the double slit and quantum algorithms as the same phenomenon
Predict before you read on
The Hadamard gate H turns |0⟩ into an even superposition: measure right after one H and you get 0 or 1, 50/50 — statistically a fair coin flip. Now start in |0⟩, apply H twice without measuring in between, then measure. What do you see?
Commit to an answer — the next section is the payoff.