Lesson 8 · 11 min
Waves That Cancel
The trick is not trying everything. It is cancelling the wrong answers.
Drop two stones in a pond. Where two crests meet, the wave gets taller. Where a crest meets a trough, the water goes flat. Qubits do this too — and it is the whole trick.
- Two ways of getting the same answer can add up, making that answer more likely.
- Or they can cancel out completely, making that answer impossible.
- A quantum computer does not check every answer. It arranges for the wrong ones to cancel.
- That is why negative tilts mattered. Without them nothing could ever cancel.
Try it
Two paths meeting
Spin it, maybe flip the hidden sign, then spin it again. The middle looks the same either way — the ending does not.
Halfway — always the same
050%
150%
After the second spin
0100%
10%
Always 0. The other answer cancelled itself out completely.
Quick check
0/31. What happens when a crest meets a trough?
2. How does a quantum computer find the right answer?
3. What do you get if you apply H twice to |0>?