# Impurities in cryogenic solids: a new platform for hybrid quantum systems

## TL;DR

This paper introduces a new hybrid quantum platform using noble gas crystals doped with spin impurities on superconducting resonators, enabling strong coupling and coherence measurements at cryogenic temperatures for quantum research and technology development.

## Contribution

The authors develop a novel hybrid quantum system combining noble gas crystals with spin impurities and superconducting resonators, demonstrating strong coupling and coherence at millikelvin temperatures.

## Key findings

- Achieved strong coupling between impurity ensemble and resonator.
- Measured coherence times of the impurity spins.
- Demonstrated potential for exploring quantum phenomena and technologies.

## Abstract

Hybrid quantum systems offer a promising platform for studying quantum phenomena and developing applied technologies, benefiting from the individual strengths of their components. Here, we present a novel hybrid quantum platform composed of solid noble gas crystals doped with spin impurities atop superconducting resonators. The noble gas crystals provide a soft, inert, predominantly spin-0 host matrix for the atomic impurities, while the alkali atoms have addressable and long-lived hyperfine transitions in the GHz regime. We demonstrate the ability to reach the strong coupling regime between the atomic impurity ensemble and the superconducting resonator at mK temperatures, and perform coherence time measurements. Our proof-of-principle measurements show that this platform offers a unique architecture for exploring fundamental quantum effects and new quantum technologies.