Tunable on-chip filter for qubit control and reset

Qubit control and reset are essential operations for quantum information processing. Current approach requires different circuit elements to address these operations individually. In our work, we designed a tunable on-chip filter for the qubit drive that enables simultaneous fast control and suppressed decay to the drive line, and allows rapid reset of the qubit to its ground state. Based on our previous work, this filter acts as a stopband at the qubit frequency but couples strongly at one-third of that frequency. This design decouples the qubit from the drive line at the qubit frequency, while allowing control through subharmonic resonance drive.

We extend this approach by making the filter frequency-tunable, offering advantages over the fixed-frequency design: (a) by maintaining long coherence times without the need to tune the qubit away from its zero-bias sweet spot to match the filter stopband; and (b) faster qubit reset by shifting the stopband away from the qubit frequency to enhance spontaneous decay. Experimentally, we achieve over 1 GHz of tunability, providing flexibility to match the stopband across various qubit frequencies due to uncertainty in fabrication. We also present single-qubit gate benchmarking and single-shot readout fidelity to evaluate the filter’s performance.