- Prepare the same state
- Measure once
- Record 0 or 1; repeat
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State and observation are different
A qubit can be prepared in a superposition of the states labeled 0 and 1. Its amplitudes determine the probabilities for a chosen measurement. Measuring in the computational basis gives one bit: 0 or 1. You do not get a list of all possible answers.
Sources: IBM Quantum Learning
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Repeat the preparation
Prepare an ideal equal superposition and measure it repeatedly, starting afresh each time. Roughly half the outcomes are 0 and half are 1 across many trials; a short run need not split evenly. Reading one trial does not reveal the full state.
Sources: IBM Quantum Learning
Check your understanding
Does one measurement reveal both possible answers?
Reveal the answer
No. One computational-basis measurement produces one outcome. Repeated preparations let you estimate outcome probabilities.
Sources and review scope
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