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Operation of Unshielded Kinetic-Inductance Traveling-Wave Parametric Amplifiers in Multi-Tesla Fields
Christian Boutan, Erik Lentz, Corwin Shiu, Deniz Erdag, Stephen Jones, Joseph Van Vlack, Logan Howe, Andrea Giachero, Paul Szypryt, Michael Vissers, Jason Austermann, Johannes Hubmayr, Stefan Knirck, Douglas Bennett, Joel Ullom
TL;DR
Existing Josephson parametric amplifiers are sensitive to magnetic fields, motivating alternatives for quantum-limited RF measurements near strong-field environments. This paper tests KTWPAs across magnetic-field strength, orientation, bias, and pump conditions, finding they retain roughly 10 dB gain under 1 T when oriented parallel to the device plane.
Problem
Josephson parametric amplifiers offer near-quantum-limited amplification but are sensitive to O(mT) magnetic fields and have limited instantaneous bandwidth.
Method
The authors characterize two KTWPAs from 4–10 GHz under 0–1.5 T fields while varying orientation, bias current, and pump conditions.
Results
~10 dB gain persists under 1 T applied field for parallel orientation, whereas perpendicular devices produce no net gain by 20 mT.
Takeaways & Limitations
KTWPAs show magnetic-field-resilient gain that supports their potential use for quantum-limited RF measurements near Tesla-scale fields.
Takeaways & Limitations
A follow-up study is still needed to assess these KTWPAs’ effectiveness in axion haloscope searches, including system gain and noise over multiple magnet ramps and quenches.
Abstract
from arXiv · showhide
Cryogenic parametric amplifiers are used to amplify radio-frequency signals for a range of applications in basic and applied science. Both Josephson Parametric Amplifiers and Josephson Traveling-Wave Parametric Amplifiers have been used as first-stage amplifiers enabling readout chains operating within a few quanta of the quantum limit. However, these devices are highly sensitive to magnetic fields, having critical current suppressed by the Fraunhofer effect, requiring substantial field-free zones. In a dark matter axion search experiment, axions convert to detectable microwave photons in the presence of a strong magnetic field, necessitating amplifiers that can reliably operate close to these environments. Kinetic-inductance Traveling-Wave Parametric Amplifiers (KTWPAs) may be the ideal candidate for this type of application having high critical magnetic field of the materials used throughout their construction. In this letter we demonstrate that KTWPAs can provide high gain (>20dB) over a multi-GHz bandwidth in spite of from multiple exposures to multi-Tesla fields. Further, we explore operational characteristics of these devices under harsh conditions as a function of overall field strength, device orientation within the field, applied bias current, and pump power & frequency. In so doing, we find KTWPA gain vanishes in devices oriented perpendicularly to a field of 0.02T, but gain values >10dB are achievable in fields over 1T when oriented near~parallel to the device plane, with peak gain achieved with an applied 0.25T to 0.5T field. It is our expectation that KTWPAs will expand the accessibility of quantum-limited RF measurements in the presence of Tesla-scale fields.
Appendix A: Supplementary Information: Experimental Setup
The experiments were conducted at PNNL with two KTWPAs installed near the center of a dilution-refrigerator magnet bore. The setup supported perpendicular and parallel device orientations, cryogenic RF conditioning, combined pump and bias delivery, and transmission measurements.
- Cryogenic and magnet setup: Two KTWPAs were mounted near the magnet-bore center of a BlueFors LD400 dilution refrigerator at PNNL.They were attached to an OFHC copper manifold and gold-plated copper cold finger at the dilution refrigerator mixing-chamber plate.
- Cryogenic and magnet setup: The manifold placed one device perpendicular and the other parallel to the bore’s vertical magnetic field, designated KTWPA⊥ and KTWPA∥.These orientations enabled comparison of device response relative to the applied field direction.
- RF chain and thermalization: The RF chain used 40 dB input attenuation, multistage thermal sinking, low-pass filtering, bias-tees, pump injection, and output isolation.The cryostat stages included 50 K, 4 K, 1 K, 100 mK, and 10 mK, with the MXC reaching up to 90 mK during measurements.
- Room-temperature instrumentation: A Yokogawa GS210 current source, SignalCore SC5511A tone generator, and S5180B Copper Mountain VNA supplied bias, pump, and RF transmission measurements.The VNA tested transmission properties across the KTWPAs’ input and output lines.