FA-90859 / Quantum circuit simulation / Member archive

Statevector S-dagger rotates the wrong way · case 04

H followed by Sdg yields the |+i> state instead of |-i>, so a subsequent measurement basis change reports the wrong eigenstate.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

Input [n, gates]; start in |0...0>, apply gates h,x,y,z,s,sdg,t (["g", q]) and cx,cz,swap (["g", a, b]) with qubit 0 as the least significant bit of the basis index; return the statevector as [re, im] pairs rounded to 6 decimals.

Why this case matters

Statevector simulators underpin circuit unit tests; a gate-kernel slip silently corrupts every downstream amplitude.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression: random circuit 32	`[[0.0, 0.0], [-1.0, 0.0]]`	`[[0.0, 0.0], [1.0, 0.0]]`	Failed

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