State Collapse

When a quantum system in a superposition is measured, the measurement produces one of the possible outcomes, and the system is projected onto the corresponding measurement state. As a result, the original superposition is no longer available in that measurement basis.

For example, if a qubit is in the state

∣ψ⟩=α∣0⟩+β∣1⟩,

a measurement in the computational basis produces:

This process is commonly called wave-function collapse or state collapse. More precisely, the state is updated according to the measurement outcome and the basis in which the measurement is performed.