Passive filters.
Measurable gains.

HERD is a patented infrared-blocking filter for superconducting quantum processors. It removes high-energy radiation that breaks Cooper pairs while leaving your microwave signals essentially untouched, improving qubit coherence and readout without redesigning your stack.

Application noteOriginal paper

Break the IR trade-off

HERD filters provide more than 60 dB attenuation above typical Cooper-pair breaking frequencies while keeping in-band insertion loss below a few tenths of a decibel. You no longer have to choose between low-insertion loss and high-frequency absorption.

Protect coherence and readout

By draining high-energy radiation before it reaches the qubit chip, HERD reduces quasiparticle-inducing noise that limits coherence. Experiments using HERD-2 report sub-Hz quasiparticle tunneling rates, state-of-the-art coherence and QND readout fidelities around 99.93% in superconducting circuits.

Built for cryostats

HERD-2 is a compact, non-magnetic, SMA inline component designed for high-density cryostats. Performance is validated up to 145 GHz and has exceptionally low unit-to-unit performance variation and reliable cool-down behavior.

Research

Validation 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.

2025
Yale University
Quasiparticle bursts

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.
https://doi.org/10.48550/arXiv.2505.08104
2025
Yale University
NbN junctions

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.
https://doi.org/10.48550/arXiv.2510.19983
2025
Yale University
Qubit readout

Benchmarking the readout of a superconducting qubit for repeated measurements

Introduces a benchmarking protocol that directly measures readout-induced leakage in superconducting qubits, showing that leakage can vary from ~0.1% to ~8% at fixed high assignment fidelity.
https://doi.org/10.1103/PhysRevLett.134.100601
2025
University of Cologne
Vortex states, superconductivity

Quantum Coherence in Superconducting Vortex States

Demonstrates coherent quantum dynamics associated with Abrikosov vortices and investigates how vortex physics impacts superconducting devices.
https://doi.org/10.48550/arXiv.2510.19769
2025
Chalmers University of Technology
Quantum thermodynamics, qubit reset

Thermally driven quantum refrigerator autonomously resets a superconducting qubit

Autonomous quantum absorption refrigerator built from superconducting circuits that cools a transmon below the temperature of any individual bath and achieves record-low effective qubit temperature for reset.
10.1038/s41567-024-02708-5
2025
Yale University
Parametric amplifiers, readout

Lumped-element broadband SNAIL parametric amplifier with on-chip pump filter for multiplexed readout

SNAIL-based broadband parametric amplifier with integrated matching network and on-chip pump filter enabling wideband, high-gain, pump-isolated multiplexed readout.
10.1103/PhysRevApplied.23.024034
2025
EPFL
Cavity design

Raising the Cavity Frequency in cQED

Studies how raising cavity frequencies in circuit-QED modifies coupling, decoherence channels, and design trade-offs for superconducting qubit architectures.
10.48550/arXiv.2501.01002
2025
Yale University
Qubit readout

High-frequency readout free from transmon multi-excitation resonances

Demonstrates high-frequency off-resonant readout where the resonator is detuned far above the transmon, suppressing multi-excitation resonances and achieving ~99.93% QND fidelity with negligible leakage.
https://doi.org/10.48550/arXiv.2501.09161

Questions

Find answers to common questions about HERD and how it works.

On which lines should I use HERD?

Start with readout and drive lines where you care most about coherence, QND fidelity, and minimizing loss between the qubit and first amplifier stage. HERD is particularly valuable on lines where conventional absorptive IR filters would add unacceptable in-band loss or dispersion.

How does HERD compare to absorptive IR filters or multi-stage LC filters?

Absorptive filters (Eccosorb, copper-powder) provide strong IR attenuation but always introduce in-band loss and dispersion. LC / resonant filters are flatter in-band but leak at very high frequencies and often have parasitic paths. HERD is designed to combine the good parts of both: near-ideal low-loss transmission in the qubit band with stop-band attenuation exceeding 60 dB at high frequencies, and no obvious parasitic leakage paths.

At which temperature stage should HERD sit?

Most partners place HERD at or near the mixing-chamber stage, often as close to the sample package as mechanical constraints allow. Some setups also use HERD at higher stages as part of a multi-stage shielding strategy. The optimal choice depends on your attenuator distribution and shielding; we can review this together before shipment.

What about magnetic materials and cryogenic reliability?

HERD hardware uses carefully selected non-magnetic materials and platings, with repeated thermal cycling and cryogenic tests as part of the qualification process. Unit-to-unit variations are controlled in production, which is not the case for many “home-built” absorptive filters.

Need more information?

Contact