Full Quantum Process Tomography of a Universal Entangling Gate on an IBM’s Quantum Computer
M. AbuGhanem
Abstract
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 $$\sqrt{\text {SWAP}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mtext>SWAP</mml:mtext> </mml:msqrt> </mml:math> and $$\sqrt{\text {CZ}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mtext>CZ</mml:mtext> </mml:msqrt> </mml:math> 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 $$97.27\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>97.27</mml:mn> <mml:mo>%</mml:mo> </mml:mrow> </mml:math> (quantum simulator) and $$88.99\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>88.99</mml:mn> <mml:mo>%</mml:mo> </mml:mrow> </mml:math> (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.