Lesson 7 · 10 min
Moves You Can Make
Every quantum move can be undone. That is the rule.
A gate is a move you make on a qubit. Flip it. Put it in a spin. Nudge its tilt. There are only a few basic moves, and everything else is made of them.
- X is the flip: 0 becomes 1, 1 becomes 0. The same move a plain computer makes.
- H is the spinner: it takes a settled qubit and puts it exactly half and half.
- Z leaves the odds alone and changes the hidden sign — which sounds useless until two paths meet.
- Every quantum move can be run backwards to undo it. There is no quantum move that forgets.
Try it
Try the moves
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X flips · H spins · Z changes the hidden sign
Quick check
0/31. What does the X gate do to |0>?
2. What does H do to a settled qubit?
3. Why can every quantum gate be undone?