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Glossary

Quantum glossary

Superposition

A quantum state that is a weighted combination of basis states, with complex amplitudes.

It is not “being in both states at once” in the everyday sense, and not ignorance of a hidden answer. It is a single, definite state — one that simply is not one of the basis states you chose to measure in.

|ψ⟩ = Σₓ αₓ|x⟩

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Related terms

  • Amplitude — The complex number attached to each possible outcome of a quantum state; its squared magnitude is that outcome’s probability.
  • Interference — Amplitudes for the same outcome adding up (constructive) or cancelling (destructive).
  • Measurement — Reading out a qubit, which returns a classical bit sampled by the Born rule and leaves the qubit in the state matching it.