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SQUAT/QPD Workshop Summary

Plus Unsolicited Thoughts

Noah Kurinsky

October 29, 2025

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Questions We Had in 2018

  • Is this the best architecture…
    • For photon sensing
    • Can we also see phonons with this method?

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  • Can we use low-Tc junctions to improve signal amplification?
    • Can this be made spectroscopic?

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  • How would one apply this to different types of discovery experiments?

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�There are a lot of people involved now!

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What we know now: SQUATs Work (readout only)

  • Readout resonators are not strictly needed (SQUATs) but there are readout tradeoffs - background rates are similar to QCDs and qubits so techniques can be swapped readily

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What we know now: QPDs Work (readout only)

  • QCDs can be converted to QPDs by complete re-design of the island to have a large capture volume�
  • SQUAT vs QPD architectures are easily interchangeable in that the SQUAT + resonator is an OCS transmon

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What we know now: Measurement Techniques

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Commercial

QICK

SMuRF

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Readout Developments

  • Readout options abound!
    • QICK
    • SMuRF
    • Commercial Options

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  • We have a variety of platforms to test many of these new readout schemes - but work is needed!

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Tracking On

Legacy SMuRF system

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Packaging Developments

  • Enclosure designs are improving rapidly with better models of mm-wave propagation
  • Many stages of pair-breaking radiation mitigation are needed!

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Packaging Developments: We will keep iterating

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Vibration Isolation is Hard

Some progress can be made with commercial solutions

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The low-vibration fridges really are good

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SQUATs seem to care! Qubits do too but more is not always better.

Noise PSD for HVeV detector mounted on vibration stage at SLAC vs. HVeV installed at CUTE

Olaf Run 17

CVIP3 vibration isolation stage

SPLENDOR payload

Cryoperm magnetic shielding + HVeV payload (hidden)

Oxford Proteox mixing chamber plate

CVIP3 vibration isolation stage

HVeV detector stack

Cryoperm magnetic shielding

Oxford Proteox mixing chamber plate

Olaf Run 15

Cryoperm magnetic shielding (installed after image taken)

No isolation

No isolation

w/ isolation

w/ isolation

PT on

PT off

PT on

PT off

TAMU HVeV detectors noise PSDs

NFC1 No isolation PT on

NFC1 No isolation PT off

NFC3 w/ isolation PT on

NFC3 w/ isolation PT off

SiC NFC HVeV detectors noise PSDs

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There’s a lot of awesome design work going on!

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And Simulations Too!

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Fab has Picked Up Substantially

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Calibration Options are Rapidly Advancing

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Quantum-Limited Readout is Here and Improving

Floquet J-TWPA(MIT)

KI-TWPA(JPL)

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A Snapshot of Where We Are

  • We have working architectures
  • We have realistic packaging plans
  • Our backgrounds are reducing
  • Our readout is maturing
  • Quantum limited readout will happen
  • Low-Tc junctions are becoming a reality
  • Calibration options are increasing and maturing

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We have a real collaboration and it’s working

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Let’s put all of this together and go do some science!

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Give Us Feedback!

Let us know what you liked and what you didn’t!

  • Was this useful for your work?
  • Was the level of detail right?
  • Do you want more workshops?
  • Do you like us?
  • Do you have a logo idea?
  • What are we doing wrong?
  • What physics haven’t we considered?

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