Work

Cryogenic high-Q passive hanger type drive-line notch filtering for leakage-resilient qubit control

Year: 2026

Type: article

Abstract: Short control pulses broaden spectrally and drive unwanted ∣1⟩↔∣2⟩ transitions in weakly anharmonic qubits. We introduce a passive hardware mitigation: a capacitively coupled λ/4 hanger resonator on the qubit drive line, creating a notch at f 12 while leaving f 01 largely unaffected. Implemented as a superconducting device at millikelvin temperature, the filter exhibits high Q i and a sharply localized, low-loss stopband. The coupling capacitance sets Q c , enabling lithographic tuning of notch depth and linewidth. Simulations and cryogenic S 21 measurements confirm a well-defined minimum with minimal off-resonant distortion. Integrated in a qubit setup, the filter suppresses short-pulse leakage: spectroscopy reduces the f 12 feature and IQ-plane data show a stable ∣e⟩ cluster; at l = 6 ns the f 12 peak-height ratio drops by ~ 7 dB. The approach is fully passive, wiring-free, and scalable, and complements DRAG by allowing shorter envelopes or smaller DRAG weights.

Source: EPJ Quantum Technology

DOI: 10.1140/epjqt/s40507-026-00508-9