Passive filters.
Measurable gains.
A patented filter that removes Cooper-pair-breaking radiation
from cryostat wiring, leaving microwave signals untouched.
Breaking the IR trade-off
Coaxial cryostat wiring channels infrared photons into the millikelvin environment. At energies above the ~80 GHz Cooper-pair breaking threshold, these photons generate quasiparticles, one of the dominant decoherence mechanisms in state-of-the-art superconducting processors.
Conventional absorptive filters block infrared radiation but introduce severe insertion loss across the 4-8 GHz passband used for qubit control and readout. Protecting the qubit and preserving the signal have, until now, been mutually exclusive.
HERD resolves this by exploiting a leaky coaxial waveguide geometry that is selectively lossy above its cutoff frequency. Below 14 GHz, the signal passes with less than 0.15 dB loss. Above 70 GHz, radiation couples out through deliberate leakage paths, achieving greater than 60 dB attenuation validated to 145 GHz.
The science behind HERD
The original physics paper and engineering integration guide for teams deploying HERD in cryogenic quantum setups.
Engineering Integration
HERD Family Application Note
Practical guidance on integrating HERD filters into dilution refrigerator wiring. Covers placement, thermal anchoring, connector configurations, and real-world performance data.
Download PDF
Peer-Reviewed Paper, 2022
Low-pass filter with ultra-wide stopband for quantum computing applications
By Robert Rehammar and Simone Gasparinetti. Describes the leaky waveguide mechanism with measurements from DC to 145 GHz.
Read on arXivValidation from the field
HERD filters are used in state-of-the-art experiments on superconducting qubits, including work on quasiparticle tunneling, coherence and high-fidelity readout.
Raising the Cavity Frequency in cQED
Demonstrates raising cavity frequency to 21 GHz while maintaining a standard 5 GHz transmon qubit. Achieves 8% quantum efficiency readout, qubit quality factor exceeding 10⁷, and coherence times reproducibly exceeding 100 μs.
A transmon qubit realized by exploiting the superconductor-insulator transition
Demonstrates a transmon-type qubit made from an NbN thin film weak link created by tuning near the superconductor–insulator transition. The junction-less design avoids oxide barriers and parasitic capacitance, showing feasibility of planar, high-gap superconducting qubits.
Co-designed reflective and leaky-waveguide low-pass filter for superconducting circuits
Presents a stepped-impedance low-pass filter with integrated hollow waveguide absorbers. Achieves 3 dB cutoff at 13.5 GHz, insertion loss below 0.45 dB under 8 GHz, and more than 52.7 dB rejection above 17.3 GHz.
Recovery dynamics of a gap-engineered transmon after a quasiparticle burst
Gap-engineered transmons show reduced sensitivity to quasiparticle bursts. Burst rates drop by a factor of a few, but elevated substrate temperature during radiation impacts lets quasiparticles overcome the engineered gap. Relaxation recovers in ~0.7 ms, while chip heating persists for several milliseconds, revealing limits of gap engineering without improved phonon evacuation.
Lumped-element broadband SNAIL parametric amplifier with on-chip pump filter for multiplexed readout
Describes a broadband SNAIL amplifier with integrated matching network and on-chip pump filtering, enabling wideband multiplexed qubit readout with improved isolation.
2D transmons with lifetimes and coherence times exceeding 1 millisecond
Tantalum transmons on high-resistivity silicon achieve 2D qubit lifetimes up to ~1.7 ms and echo coherence exceeding T₁, while supporting 99.994% single-qubit gate fidelity on a wafer-scalable platform.
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