Giallar: Push-Button Verification for the Qiskit Quantum Compiler

TL;DR

Giallar is an automated, specification-free verification toolkit for quantum compiler passes, capable of handling complex semantics and unbounded loops, demonstrated on Qiskit with effective bug detection and minimal performance impact.

Contribution

Giallar introduces a novel automated verification approach for quantum compilers that requires no manual invariants or proofs, handling unbounded loops and complex semantics.

Findings

Verified 44 out of 56 Qiskit compiler passes

Detected and confirmed 3 bugs in Qiskit

Most passes verified within seconds with modest overhead

Abstract

This paper presents Giallar, a fully-automated verification toolkit for quantum compilers. Giallar requires no manual specifications, invariants, or proofs, and can automatically verify that a compiler pass preserves the semantics of quantum circuits. To deal with unbounded loops in quantum compilers, Giallar abstracts three loop templates, whose loop invariants can be automatically inferred. To efficiently check the equivalence of arbitrary input and output circuits that have complicated matrix semantics representation, Giallar introduces a symbolic representation for quantum circuits and a set of rewrite rules for showing the equivalence of symbolic quantum circuits. With Giallar, we implemented and verified 44 (out of 56) compiler passes in 13 versions of the Qiskit compiler, the open-source quantum compiler standard, during which three bugs were detected in and confirmed by Qiskit. Our evaluation shows that most of Qiskit compiler passes can be automatically verified in seconds and verification imposes only a modest overhead to compilation performance.