Multi-mode technique for the determination of the biaxial Y2SiO5 permittivity tensor from 300 to 6 Kelvin

TL;DR

This study introduces a multi-mode microwave measurement technique to determine the biaxial permittivity tensor of Y2SiO5 across a temperature range from 300 to 6 Kelvin, providing essential data for quantum device applications.

Contribution

The paper presents the first microwave characterization of Y2SiO5's permittivity tensor and a novel multi-mode method for its measurement at cryogenic temperatures.

Findings

Permittivity tensor components were accurately measured with uncertainties below 0.26%.

The temperature dependence of the tensor components was characterized from 296 K to 6 K.

Electrical Q-factors of modes provided insights into crystal losses at low temperatures.

Abstract

The Y2SiO5 (YSO) crystal is a dielectric material with biaxial anisotropy with known values of refractive index at optical frequencies. It is a well-known rare-earth (RE) host material for optical research and more recently has shown promising performance for quantum-engineered devices. In this paper, we report the first microwave characterization of the real permittivity tensor of a bulk YSO sample, as well as an investigation of the temperature dependence of the tensor components from 296 K down to 6 K. Estimated uncertainties were below 0.26%, limited by the precision of machining the cylindrical dielectric. Also, the electrical Q-factors of a few electromagnetic modes were recorded as a way to provide some information about the crystal losses over the temperature range. To solve the tensor components necessary for a biaxial crystal, we developed the multi-mode technique, which uses simultaneous measurement of low order Whispering Gallery Modes. Knowledge of the permittivity tensor offers important data, essential for the design of technologies involving YSO, such as microwave coupling to electron and hyperfine transitions in RE doped samples at low temperatures.