# Low-Temperature Microwave Properties of Biaxial YAlO3

## TL;DR

This study characterizes the microwave dielectric properties and spin interactions of YAlO3 crystals at cryogenic temperatures, revealing their potential for quantum hybrid systems through detailed permittivity tensor measurements and electron spin resonance spectroscopy.

## Contribution

It provides the first detailed temperature-dependent permittivity tensor of YAlO3 and identifies new ESR transitions, advancing understanding of its suitability for quantum applications.

## Key findings

- YAlO3 is biaxial with permittivity tensor characterized below 0.26% uncertainty.
- New ESR transitions with zero-field splittings of 16.72 and 9.92 GHz were discovered.
- Spin-photon couplings of 4.2 and 8.4 MHz were observed, exceeding cavity linewidths.

## Abstract

Low-loss crystals with defects due to paramagnetic or rare earth impurity ions is a major area of investigation for quantum hybrid systems at both optical and microwave frequencies. In this work we examine the single crystal yttrium aluminium perovskite, YAlO$_3$ using the Whispering Gallery Mode Technique. Multiple resonant microwave modes were measured from room temperature to 20 mK allowing precise characterization of the permittivity tensor at microwave frequencies. We show that it is biaxial and characterize the tensor as a function of temperature with estimated uncertainties below 0.26%. Electron spin resonance spectroscopy was also performed at 20 mK, with new transitions identified with Zero-Field splittings of 16.72 and 9.92 GHz. Spin-photon couplings of order 4.2 and 8.4 MHz were observed for residual levels of concentration, which are stronger than the photon cavity linewidths of 116 kHz but the same order of the linewidths of the discovered spin transitions.