In Situ Interferometric Spatial Mapping Of A Microwave Kinetic Inductance Detector Array

TL;DR

The paper introduces a cryogenic interferometric method for spatially mapping MKID arrays, enabling precise localization of superconducting resonators in dense configurations for astrophysical applications.

Contribution

A novel in situ interferometric technique using a superconducting transmission line for accurate spatial mapping of MKID arrays in cryogenic environments.

Findings

Successfully mapped a 44 pixel MKID array with 900 μm spacing.

Demonstrated phase measurement correlates with physical positions of MKIDs.

Method suitable for dense, kilopixel MKID arrays in astrophysics instruments.

Abstract

We present a method of spatially mapping microwave kinetic inductance detector (MKID) arrays, in a dark setup. MKIDs are superconducting natively multiplexed resonators which enable kilopixel arrays, such as for the proposed Probe far-Infrared Mission for Astrophysics (PRIMA). In such telescope applications one must map the spatial location of each MKID with their individual resonance frequencies. Traditional LED arrays or beam-mapping methods become increasingly difficult as pixel spacing decreases, e.g., 900 {\mu}m separated MKIDs in the spectrometer module of PRIMA. Our new mapping technique uses a cryogenic interferometer in reflection mode. As on-resonance signals reflect from an MKID, they accrue a phase proportional to the path-length, exactly corresponding to their physical distance on the feedline. Specifically, we use a superconducting transmission line that has nonlinear kinetic inductance. The slow-wave structure of this nonlinear device is designed to have a signal speed of 0.64% the speed of light, enabling a compact system. Current biasing this line allows for varying the wave speed and ensuring that the phase measured is periodic within a nulling interferometric mode. Using this setup, we measure a length ordering that reflects the bimodal MKID distribution of a 44 pixel array of MKIDs designed for PRIMA which contains the same spacing as the final kilopixel array design.