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Assessing the operating characteristics of an ion-milled phonon-mediated quantum parity detector

Brandon J. Sandoval, Andrew D. Beyer, Pierre M. Echternach, Sunil R. Golwala, William D. Ho, Lanqing Yuan, Karthik Ramanathan·September 23, 2025
physics.ins-detastro-ph.IMhep-exQuantum Physics

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Abstract

Phonon sensitive superconducting qubits promise to provide sub-eV energy deposit thresholds, useful for future rare-event experiments looking for interactions from dark matter and neutrinos. We detail here engineering results from a Quantum Parity Detector (QPDs), one of a class of phonon sensitive qubits, and, as a first measurement, show that this device has a quiescent quasiparticle density of $1.8 \pm 0.8 μ\mathrm{m}^{-3}$, in line with expectation. We also outline an argon ion-mill process for multi-step Josephson Junction fabrication, expanding the sparse literature on this topic, which proves useful in avoiding secondary parasitic junctions.

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