Retromorphic Testing of Quantum Compiler Passes
Retromorphic Testing of Quantum Compiler Passes
RetroQ combines retromorphic testing and Hadamard-test ideas to check semantic preservation and intended structural changes in quantum compiler passes.
Paper (2026-10-08, arXiv:2610.11195) — Mushahid Khan and Olivia Di Matteo. Paper
What it does
Quantum compiler passes are difficult to validate because the expected output of large entangled circuits is often hard to compute. The authors analyze unit tests in PennyLane, Qiskit, Cirq, and pytket, finding that tests mainly use program-content and circuit-metric assertions and are usually small and shallow.
They propose a pass-specific retromorphic testing method and implement RetroQ. Given a pass, a test circuit, and expected pass behavior, the method checks semantic preservation and intended structural changes, using ideas related to the Hadamard test. Experiments on PennyLane and Qiskit reproduce known bugs and find defects in symbolic parameters, commutation, self-adjoint gate recognition, and runtime behavior.
Contributions
- A survey of existing quantum compiler-pass testing practices.
- A method that combines semantic and structural checks for transformed circuits.
- A working framework that discovers defects in real quantum software stacks.
Limits
Testing depends on selected circuits, expected behavior, and numerical thresholds; it does not prove correctness for every circuit. The experiments cover selected passes in two frameworks, and Hadamard-test checks may add execution cost.
Connections
RetroQ complements symbolic equivalence checking described in Verification Methods and Tools. Unlike QTestBench, it targets compiler transformations rather than LLM-generated test suites.
Reference
Khan and Di Matteo, Retromorphic Testing of Quantum Compiler Passes, arXiv:2610.11195, 2026.