FA-90915 / Quantum circuit simulation / Member archive

Collapse renormalizes by probability instead of its square root · case 05

After measuring |+> the post-measurement amplitude is 1.414 instead of 1.0.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

Case contract

Input [n, amps, q, outcome]; measure qubit q (0 = LSB) of the possibly unnormalized state. Return {"probability": p, "state": post} with p normalized by the total squared norm and the post-measurement state renormalized to unit norm with the other branch zeroed; values rounded to 6 decimals. Return "impossible" when p < 1e-12.

Why this case matters

Mid-circuit measurement and collapse drive dynamic circuits; wrong renormalization breaks every later probability.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression: random collapse 11	`{"probability": 0.34182, "state": [[0.0, 0.0], [-1.546542, -0.90329], [0.0, 0.0], [-0.420851, 0.191607]]}`	`{"probability": 0.34182, "state": [[0.0, 0.0], [-0.836084, -0.488332], [0.0, 0.0], [-0.227518, 0.103586]]}`	Failed

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