Experimental demonstrations of broadband quantum control of superconducting qubits with QuBE (Qubit-controller with Broadband Electronics)

We have developed a scalable qubit controller using broadband electronics that meets the stringent requirements for superconducting quantum processors. We demonstrate broadband control of fixed-frequency superconducting transmon qubits in a two-dimensional array. Utilizing both the inversion recovery and spin-echo methods implemented with the qubit controller, we achieved T₁ and T₂ of more than 60 μs. Applying the DRAG pulses synthesized, we obtained a single-qubit gate fidelity of more than 99.9%. The broadband electronics enable the execution of sequences involving multiple pulses separated in frequency by more than 1 GHz. With this capability, we achieved unconditional state cooling via driving the f0-g1 transition. We also implemented cross-resonance (CR) gates by applying the CR and single-qubit drives separated by a frequency exceeding 1 GHz through the same control ports.