# Mitigation of Cosmic Ray Effect on Microwave Kinetic Inductance Detector Arrays

## TL;DR

This study systematically tests various mitigation techniques on MKID arrays to significantly reduce cosmic ray-induced dead time, demonstrating potential for space observatories and quantum computing applications.

## Contribution

It introduces and evaluates novel mitigation strategies, including low T_c phonon absorbers and membranes, to minimize cosmic ray effects on large MKID arrays.

## Key findings

- Dead time reduced up to 40 times compared to reference.
- Simulations show dead time below 1% in space conditions.
- Mitigation techniques are applicable to quantum computing arrays.

## Abstract

For space observatories, the glitches caused by high energy phonons created by the interaction of cosmic ray particles with the detector substrate lead to dead time during observation. Mitigating the impact of cosmic rays is therefore an important requirement for detectors to be used in future space missions. In order to investigate possible solutions, we carry out a systematic study by testing four large arrays of Microwave Kinetic Inductance Detectors (MKIDs), each consisting of $\sim$960 pixels and fabricated on monolithic 55 mm $\times$ 55 mm $\times$ 0.35 mm Si substrates. We compare the response to cosmic ray interactions in our laboratory for different detector arrays: A standard array with only the MKID array as reference; an array with a low $T_c$ superconducting film as phonon absorber on the opposite side of the substrate; and arrays with MKIDs on membranes. The idea is that the low $T_c$ layer down-converts the phonon energy to values below the pair breaking threshold of the MKIDs, and the membranes isolate the sensitive part of the MKIDs from phonons created in the substrate. We find that the dead time can be reduced up to a factor of 40 when compared to the reference array. Simulations show that the dead time can be reduced to below 1 % for the tested detector arrays when operated in a spacecraft in an L2 or a similar far-Earth orbit. The technique described here is also applicable and important for large superconducting qubit arrays for future quantum computers.