Development Status of the KIPM Detector Consortium

TL;DR

This work presents the development of Kinetic Inductance Phonon-Mediated (KIPM) detectors within a multi-institutional consortium aimed at achieving sub-eV energy thresholds for substrate energy deposition, enabling light dark matter and low-energy neutrino searches. It documents current performance of the baseline KIPM architecture, identifying phonon-collection efficiency, TLS noise, and phonon dynamics as key bottlenecks, and outlines near-term and long-term strategies including multi-resonator designs, low-$T_c$ resonators, and the Phonon-Absorber-Assisted (PAA) architecture to decouple volume and efficiency. The paper details concrete progress toward improved energy resolution, with a current sensor-absorber plan achieving $\sigma_{E_\text{abs}} = 2.1$ eV and a substrate-resolution goal near $\sigma_{E_\text{dep}}$ of a few eV via enhanced $\eta$; it also introduces PAA-KIPM projections reaching $\mathscr{O}(1~\text{meV})$ in optimized geometries. The consortium’s capabilities span six fabrication facilities and multiple low-temperature testbeds, enabling rapid prototyping, broadband optical and nuclear-calibration tests, and cross-facility validation. Collectively, these efforts position KIPM detectors as a competitive platform for sub-GeV dark matter searches and neutrino-interaction studies, with scalable architectures and calibrated pathways to meV-scale energy sensitivity.

Abstract

A Kinetic Inductance Phonon-Mediated Detector is a calorimeter that uses kinetic inductance detectors to read out phonon signals from the device substrate. We have established a consortium comprising university and national lab groups dedicated to advancing the state of the art in these detectors, with the ultimate goal of designing a detector sub-eV threshold on energy deposited in the substrate, enabling searches for both light dark matter and low-energy neutrino interactions. This consortium brings together experts in kinetic inductance detector design, phonon and quasiparticle dynamics, and noise modeling, along with specialized fabrication facilities, test platforms, and unique calibration capabilities. Recently, our consortium has demonstrated a resolution on energy absorbed by the sensor of 2.1 eV, the current record for such devices. The current focus of the consortium is modeling and improving the phonon collection efficiency and implementing low-$\boldsymbol{T_c}$ superconductors, both of which serve to improve the overall energy resolution and threshold of the detectors.

Figures (5)

• Figure 1: Working principle for the KIPM detector, in which a particle scattering event produces athermal phonons that are either absorbed by the sensitive superconducting element (the inductor) or lost to other superconducting structures, device mounts, or to downconversion.
• Figure 2: Three KIPM detector design masks (labeled A, B, and C) and device names studied within our consortium, all of which feature a (2.2 cm)$^2$ silicon substrate. Orange is "dead" (insensitive) Al, green is Nb, and blue shows the sensitive Al element for which $\eta$ is evaluated. Adapted from Wen2025.
• Figure 3: The simulated phonon collection efficiency $\eta^\mathrm{sim}(x,y)$ as a function of position across a KIPM detector with design Mask B is shown by the color scale. The white outline indicates the location of the superconducting features.
• Figure 4: Comparison of best-fit pulse model parameters as a function of device temperature between the OW200127 (Mask B, left) and OW230426 (Mask C, middle & right) devices. The data for OW200127 (reproduced from Temples2024) are the best-fit fall-time constants for the two-component pulse shape model. The OW230426 plots contain both On-KID data, fit to the two-component model (solid circles), and Off-KID data which are well described by a pulse with a single exponential fall-time (open triangles), except for the two lowest temperatures which are omitted from this plot. Where not visible, the On-KID $\tau_\mathrm{p}$ points fall behind the On-KID $\kappa_\mathrm{d}$ points, highly suggestive of phonon recycling. (Right) Best-fit pulse amplitudes for the OW230426 device for the on-KID two-component model (solid circles) and off-KID one-component model (open triangles).
• Figure 5: Histogram of phonon energies binned by arrival times on the inductor for the Mask C design. The colors indicate the time distribution of phonons that have undergone a specified number of reflections before being absorbed by the inductor. The total absorbed energy (per $\mu$s) for phonons of undergoing any number of reflections is shown by the black line. The top row shows the distributions of arrival times for phonons that have reflected fewer than five times, while the bottom row is for phonons that have reflected five or more times. (Left column) "On-KID" arrival times in the first 10 $\mu$s of the event. (Middle column) "On-KID" arrival times up to 800 $\mu$s. (Right column) "Off-KID" arrival times up to 800 $\mu$s. The disparity in timescale for on- and off-KID distributions demonstrates the dominance of the delayed component for events far from the inductor, as well as the dominance of the prompt component for events originating near the inductor. Note that despite the different binning of the left column, the units of the vertical axis has been scaled to match that of the other two.