FA-91085 / Quantum circuit simulation / Member archive

Bloch vector omits the factor 2 on coherences · case 05

|+> is reported at x = 0.5, inside the sphere, although it is a pure state.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

Case contract

Input [[ar, ai], [br, bi]] for a|0> + b|1> (possibly unnormalized). Return the Bloch vector [2Re(conj(a) b), 2Im(conj(a) b), |a|^2 - |b|^2] divided by |a|^2 + |b|^2, rounded to 6 decimals, or "zero-state" when the squared norm is below 1e-12.

Why this case matters

Bloch coordinates feed visualizers and single-qubit tomography checks; sign or scale slips put states on the wrong axis.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression: random qubit 8	`[-0.219366, 0.436605, 0.212174]`	`[-0.438732, 0.873211, 0.212174]`	Failed

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This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

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