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Title: Calibrating a 99.9% Fidelity CZ Gate on a Superconducting Quantum Processor<\/p>\n
Abstract: As superconducting Quantum Processing Units (QPU)\u00a0grow larger, automated and reliable calibration of high-fidelity two-qubit remains one of the main challenges. We introduce a novel gate error characterization method, which we call the Phase-Averaged Leakage Error Amplification (PALEA) protocol, building on Floquet Calibration and Matrix Element Amplification with Dynamical Decoupling (MEADD) protocols. This method is specifically designed to coherently amplify CZ gate errors, especially their associated population leakage to the second excited state of the higher frequency qubit, while remaining robust against other leakage processes. Together with the qubit-coupler coupling optimization, we use it to achieve a CZ gate fidelity of 99.93%, stable over a 40h period, without sacrificing the quality of other operations \u2013 we reach simultaneous single-qubit gate fidelities of 99.98%, and readout fidelities over 99.94 % in a single device.<\/p>\n