Verifying Results of the IBM Qiskit Quantum Circuit Compilation Flow

TL;DR

This paper introduces an efficient method for verifying the correctness of quantum circuit transformations in IBM Qiskit, significantly reducing verification time for large circuits compared to existing techniques.

Contribution

It presents a novel quantum circuit equivalence checking scheme tailored for IBM Qiskit, leveraging quantum properties and compilation knowledge for fast verification.

Findings

Can verify large circuits with tens of thousands of operations within seconds

Outperforms state-of-the-art techniques in runtime efficiency

Open source implementation available at GitHub

Abstract

Realizing a conceptual quantum algorithm on an actual physical device necessitates the algorithm's quantum circuit description to undergo certain transformations in order to adhere to all constraints imposed by the hardware. In this regard, the individual high-level circuit components are first synthesized to the supported low-level gate-set of the quantum computer, before being mapped to the target's architecture---utilizing several optimizations in order to improve the compilation result. Specialized tools for this complex task exist, e.g., IBM's Qiskit, Google's Cirq, Microsoft's QDK, or Rigetti's Forest. However, to date, the circuits resulting from these tools are hardly verified, which is mainly due to the immense complexity of checking if two quantum circuits indeed realize the same functionality. In this paper, we propose an efficient scheme for quantum circuit equivalence checking---specialized for verifying results of the IBM Qiskit quantum circuit compilation flow. To this end, we combine characteristics unique to quantum computing, e.g., its inherent reversibility, and certain knowledge about the compilation flow into a dedicated equivalence checking strategy. Experimental evaluations confirm that the proposed scheme allows to verify even large circuit instances with tens of thousands of operations within seconds or even less, whereas state-of-the-art techniques frequently time-out or require substantially more runtime. A corresponding open source implementation of the proposed method is publicly available at https://github.com/iic-jku/qcec.