Co-designed reflective and leaky-waveguide low-pass filter for superconducting circuits

The High-Energy Radiation Drain (HERD) filter is an ultra-low-loss filtering technique that uses leaky waveguides to absorb high-frequency radiation harmful to superconducting qubits. In this work, we extend the concept by leveraging the parasitic impedance of the leaky-waveguide structure and integrating it into a stepped-impedance low-pass filter. The result is a compact HERD filter with sharp roll-off and strong suppression of unwanted high-frequency signals.