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What is quantum measurement?
Quantum measurement ends a qubit’s superposition and returns 0 or 1, with the result chosen at random according to the amplitudes.
When a qubit is measured its superposition ends and it moves to the state matching the result. Running the same circuit again and again gives results spread according to the probabilities set by the amplitudes; that is why quantum programs are usually run hundreds or thousands of times (shots).
Measurement cannot be undone: a measured qubit loses its previous amplitudes. Quantum algorithms therefore leave measurement to the end and try to raise the probability of the right answer before measuring.
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Related packages
Related concepts
- Qubit · A qubit is the basic unit of information in a quantum computer: measured, it gives 0 or 1, but before measurement it can be in a superposition of both.
- Superposition · Superposition is the quantum state in which a qubit, before it is measured, holds the states 0 and 1 together with definite amplitudes.
- Decoherence · Decoherence is a qubit gradually losing its superposition and entanglement, its quantum properties, through unwanted interaction with its environment.