Development of an MKID frequency-to-pixel LED mapper for SPT-3G+

TL;DR

This paper introduces a cryogenic LED system integrated with readout electronics for optical mapping of MKID resonator frequencies in the SPT-3G+ detector array, aiming to improve detector yield by identifying frequency defects.

Contribution

It presents a novel cryogenic LED apparatus and its integration with readout electronics for optical mapping of MKID resonators in the SPT-3G+ camera.

Findings

Successful operation of the cryogenic LED at 300 mK

Effective integration with GHz readout electronics

Potential to enhance detector yield by defect characterization

Abstract

SPT-3G+ is the next-generation camera for the South Pole Telescope (SPT). SPT is designed to measure the cosmic microwave background (CMB) and the mm/sub-mm sky. The planned focal plane consists of 34,000 microwave kinetic inductance detectors (MKIDs), divided among three observing bands centered at 220, 285, and 345 GHz. Each readout line is designed to measure 800 MKIDs over a 500 MHz bandwidth, which places stringent constraints on the accuracy of the frequency placement required to limit resonator collisions that reduce the overall detector yield. To meet this constraint, we are developing a two-step process that first optically maps the resonance to a physical pixel location, and then next trims the interdigitated capacitor (IDC) to adjust the resonator frequency. We present a cryogenic LED apparatus operable at 300 mK for the optical illumination of SPT-3G+ detector arrays. We demonstrate integration of the LED controls with the GHz readout electronics (RF-ICE) to take data on an array of prototype SPT-3G+ detectors. We show that this technique is useful for characterizing defects in the resonator frequency across the detector array and will allow for improvements in the detector yield.