Optical coherence properties of Kramers' rare-earth ions at the nanoscale for quantum applications
Mohammed K. Alqedra, Chetan Deshmukh, Shuping Liu, Diana Serrano, Sebastian P. Horvath, Safi Rafie-Zinedine, Abdullah Abdelatief, Lars Rippe, Stefan Kröll, Bernardo Casabone, Alban Ferrier, Alexandre Tallaire, Philippe Goldner, Hugues de Riedmatten, Andreas Walther
Abstract
Rare Earth (RE) ion doped nanomaterials are promising candidates for a range of quantum technology applications. Among RE ions, the so-called Kramers' ions possess spin transitions in the GHz range at low magnetic fields, which allows for high-bandwidth multimode quantum storage, fast qubit operations as well as interfacing with superconducting circuits. They also present relevant optical transitions in the infrared. In particular, ${\mathrm{Er}}^{3+}$ has an optical transition in the telecom band, while ${\mathrm{Nd}}^{3+}$ presents a high-emission-rate transition close to 890 nm. In this paper, we measure spectroscopic properties that are of relevance to using these materials in quantum technology applications. We find the inhomogeneous linewidth to be 10.7 GHz for ${\mathrm{Er}}^{3+}$ and 8.2 GHz for ${\mathrm{Nd}}^{3+}$, and the excited state lifetime ${T}_{1}$ to be 13.68 ms for ${\mathrm{Er}}^{3+}$ and $540\phantom{\rule{0.16em}{0ex}}\textmu{}\mathrm{s}$ for ${\mathrm{Nd}}^{3+}$. We study the dependence of homogeneous linewidth on temperature for both samples, with the narrowest linewidth being 379 kHz (${T}_{2}=839$ ns) for ${\mathrm{Er}}^{3+}$ measured at 3 K, and 62 kHz (${T}_{2}=5.14\phantom{\rule{4pt}{0ex}}\textmu{}\mathrm{s}$) for ${\mathrm{Nd}}^{3+}$ measured at 1.6 K. Further, we investigate time-dependent homogeneous linewidth broadening due to spectral diffusion and the dependence of the homogeneous linewidth on magnetic field to get additional clarity of mechanisms that can influence the coherence time. In light of our results, we discuss two applications: single qubit-state readout and a Fourier-limited single photon source.