Properties of a rare-earth-ion-doped waveguide at sub-Kelvin temperatures for quantum signal processing

TL;DR

This study characterizes a rare-earth-ion-doped waveguide at sub-Kelvin temperatures, revealing enhanced coherence properties and demonstrating its potential for integrated quantum signal processing.

Contribution

It provides the first detailed characterization of Tm$^{3+}$:LiNbO$_{3}$ waveguides at sub-Kelvin temperatures, showing improved coherence times and suitability for quantum applications.

Findings

Coherence times up to 117 μs at 800 mK

Hyperfine population lifetimes up to 2.5 hours

Successful preparation of a 0.5 GHz atomic frequency comb

Abstract

We characterize the 795 nm $^3$H$_6$ to $^3$H$_4$ transition of Tm$^{3+}$ in a Ti$^{4+}$:LiNbO$_{3}$ waveguide at temperatures as low as 800 mK. Coherence and hyperfine population lifetimes -- up to 117 $\mu$s and 2.5 hours, respectively -- exceed those at 3 K at least ten-fold, and are equivalent to those observed in a bulk Tm$^{3+}$:LiNbO$_{3}$ crystal under similar conditions. We also find a transition dipole moment that is equivalent to that of the bulk. Finally, we prepare a 0.5 GHz-bandwidth atomic frequency comb of finesse $>$2 on a vanishing background. These results demonstrate the suitability of rare-earth-doped waveguides created using industry-standard Ti-indiffusion in LiNbO$_3$ for on-chip quantum applications.