Superposition, Carefully
A superposition is one definite quantum state whose amplitudes are spread over more than one outcome. It is not "0 and 1 at the same time," and it is not a hidden coin that already landed. You can prove the difference: a superposition can be turned back into a certain answer by interference, while a random coin cannot.
Why is superposition so often explained wrong?
You may have read that a qubit "is 0 and 1 at the same time." Or that a quantum computer "tries every answer at once." Both sound exciting. Both are wrong, and they lead people to wrong ideas about what quantum computers can do.
This chapter gives you the careful version. It is still simple. You will also run a test that tells a true superposition apart from a coin that is just unknown.
- What is a superposition, in plain words?
- Isn't a superposition just a coin we haven't looked at yet?
- Worked example: superposition vs hidden coin
- Run it: make the |+⟩ stateINTERACTIVE
- Try this: the superposition testINTERACTIVE
- Try this: a different superposition with the same countsINTERACTIVE
- Is a superposition special, or does it depend on how you ask?
- What about Schrödinger's cat?
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