Automatic Two-qubit Gate Calibration with QubiC*

Two-qubit gate calibration is a complex and time-consuming task. We developed an efficient and systematic method to automatically tune up a CNOT gate with QubiC - a customized FPGA-based Qubit Control system at LBNL. The native cross-resonance (CR) gate time and amplitude were identified by stacking multiple CR pulses. We applied a virtual Z gate on a degenerate prepared state, followed by an X90 gate. By scanning the Z gate phase, we projected the state to any angle in the XY-plane, and spread out the noise among different angles, which enabled us to extract the CNOT parameters from curve fitting. The CNOT finder yielded two sets of parameters for the gate, with a global phase of 90 degrees between them. The CNOT gate found by this method was validated by two-qubit randomized benchmarking (RB).