Polarisation and Temperature Dependence of Er$^{3+}$:CaWO$_4$ -- Towards a Solid-State Rare-Earth Ion-Doped Quantum Memory

TL;DR

This study explores how polarization and temperature affect the optical properties of Er$^{3+}$:CaWO$_4$, identifying a specific transition with optimal features for quantum memory use at cryogenic temperatures.

Contribution

It provides detailed analysis of polarization and temperature effects on Er$^{3+}$:CaWO$_4$ optical transitions, highlighting a transition ideal for quantum memory applications.

Findings

The $Z_1 o Y_1$ transition at 1532.6 nm is optimal at cryogenic temperatures.

The transition shows stable wavelength, narrow linewidth, and polarization independence.

It has a large absorption cross-section within the C-band.

Abstract

In the endeavour of developing quantum memories, Er$^{3+}$:CaWO$_4$ has emerged as a promising rare-earth ion-doped (REID) crystal platform due to its long optical coherence times and compatibility with the 1550 nm telecommunications band. This work investigates the effects of polarisation and temperature on the absorption strength, central wavelength, and linewidth of the $Z_1\to Y_1$ and $Z_1\to Y_2$ optical transitions, with light incident along the crystal $a$ and $c$ axes. It is found that the $Z_1\to Y_1$ transition at 1532.6 nm with the incident laser along the $c$-axis at cryogenic temperatures ($\sim$3 K) is particularly favourable. The transition exhibits a stable central wavelength, narrower linewidth, polarisation independence, larger absorption cross-section, and lies within the C-band -- attributes that make it highly suitable for quantum memory applications.