FA-91094 / Quantum circuit simulation / Member archive

Bloch vector only rejects an exactly zero state · case 04

Amplitudes of order 1e-7 (numerical noise) are blown up into a unit Bloch vector instead of "zero-state".

Member previewVariant 4 · 3 implementations · 6 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: noise on one amplitude	`[0.0, 0.0, 1.0]`	`"zero-state"`	Failed

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

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