FA-90934 / Quantum circuit simulation / Member archive

Pauli expectation maps the leftmost character to qubit 0 · case 04

<ZI> on |01> (qubit 0 excited) evaluates to -1 instead of +1.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

Input [n, amps, pauli]; pauli is an n-character string over I,X,Y,Z whose rightmost character acts on qubit 0 (LSB). Return the real expectation <psi|P|psi>/<psi|psi> rounded to 6 decimals. Errors: "length-mismatch", "bad-pauli" (any character outside uppercase IXYZ).

Why this case matters

Pauli expectation values are the observable layer of variational algorithms; string-order or phase slips bias every energy estimate.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression: random expectation 19	`-0.233747`	`-0.70921`	Failed

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