FA-90907 / Quantum circuit simulation / Member archive

Collapse outcome test drops parentheses around the bit extraction · case 02

Projecting qubit 1 onto outcome 1 reports "impossible" even when that qubit is certainly excited.

Member previewVariant 2 · 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 38	`"impossible"`	`{"probability": 0.475302, "state": [[0.0, 0.0], [0.0, 0.0], [-0.440491, 0.425233], [0.059042, 0.472334], [0.0, 0.0], [0.0, 0.0], [0.084914, 0.000663], [0.508157, 0.364864]]}`	Failed

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