FA-91294 / Quantum circuit simulation / Member archive

Rotation merger cancels X gates on different qubits · case 04

x on qubit 0 followed by x on qubit 1 cancels both.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

Input a gate list: ["rz", q, angle] (angle in units of pi as a fraction string), ["x", q], ["h", q], ["cx", c, t]. Scan left to right; a new gate looks back to the last op touching its qubit, except that rz may look past a cx whose control is that qubit. rz merges into a found rz, angles normalized to (-1, 1] and zero rotations dropped; x or h cancels a found identical gate. Return the optimized list with angles as fraction strings.

Why this case matters

Rotation merging and cancellation are the cheapest transpiler wins; commutation or normalization slips change circuit semantics.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression: random peephole 27	`[["x", 2], ["cx", 0, 1], ["rz", 0, "-3/4"], ["h", 0], ["x", 2]]`	`[["cx", 0, 1], ["rz", 0, "-3/4"], ["h", 0]]`	Failed

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