Ideal projective measurement
Projectors determine outcome probabilities and conditional states.
Key knowledge
For orthogonal projectors P_r summing to identity, an ideal projective measurement in normalized state ψ gives p_r = ⟨ψ|P_r|ψ⟩ and, for p_r > 0, conditional state P_rψ/√p_r.
Values and equations
P_rP_s = δ_rs P_r; Σ_r P_r = I; p_r = ⟨ψ|P_r|ψ⟩; ψ_r = P_rψ/√p_r (p_r > 0)
- P_r
- Orthogonal outcome projector
- I
- Identity operator
- δ_rs
- Kronecker delta
- p_r
- Outcome probability
- ψ, ψ_r
- Initial and conditional normalized states
Conditions and scope
- This is the ideal Lüders projective model, including degenerate outcome subspaces.
- General measurement devices may require broader measurement operators; an outcome of zero probability has no defined conditional state here.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Measurement-operator probability, completeness and normalization rules, restricted here to orthogonal projectors.
2026-10-10 · Pure-state ideal projective rule only; arbitrary device dynamics and general POVMs excluded.
Entry details
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- physics-projective-measurement
- Revision
- university-reference.1
- Structured reference record
- University reference · University core expansion