Full Quantum Process Tomography of a Universal Entangling Gate on an IBM’s Quantum Computer

Abstract

Characterizing quantum dynamics is critical in quantum physics, quantum information science, and computation, where the precision of quantum gates plays a key role. We present a comprehensive experimental analysis of the SQSCZ gate–a novel universal two-qubit entangling gate combining SWAP\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sqrt{\text {SWAP}}$$\end{document} and CZ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sqrt{\text {CZ}}$$\end{document} operations–on superconducting quantum hardware. Leveraging quantum process tomography via the Choi-Jamiołkowski isomorphism, we benchmark the gate’s performance across different noise environments. Experimental results demonstrate high process fidelities of 97.27%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$97.27\%$$\end{document} (quantum simulator) and 88.99%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$88.99\%$$\end{document} (quantum hardware), revealing remarkable noise resilience. Owing to its hybrid architecture, circuit depth reduction capabilities, and hardware-efficient decomposition into only two CNOT gates, the SQSCZ gate holds strong potential for near-term quantum applications, including the Quantum Fourier Transform and Variational Quantum Eigensolvers for molecular simulations. These findings establish the SQSCZ gate as a promising primitive for NISQ-era quantum algorithms, while providing key insights into gate-level error processes in superconducting quantum processors.