The Born Rule | Quantum Measurement Probabilities & State Collapse
Quick Technical Answer:
Formulated by Max Born in 1926, the Born rule states that the probability of obtaining measurement outcome |i⟩ from a quantum state |ψ⟩ = ∑ c_i |i⟩ equals the absolute square of its complex probability amplitude: P(i) = |c_i|².
Formula / Unitary:
P(i) = |\langle i | \psi \rangle|^2 = |c_i|^2, \quad \sum_i P(i) = 1
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Frequently Asked Questions
What happens to the relative phase of a quantum state after measurement?
Upon measurement, the state collapses irreversibly into an eigenstate corresponding to the observed outcome, erasing all relative phase information between superposition components.