Femtosecond Laser Writing of Er: LiNbO₃ Single Crystals for use as Photonic Quantum Memory

Sustaining quantum communication networks over large distances faces a significant challenge due to high loss. The quantum repeater solves this problem but requires a suitable quantum memory to function.

Using a fs pulsed laser, we have fabricated 3D LiNbO₃ single crystal architecture within a glass. Fabrication of Er doped crystals is achieved by introducing erbium to the glass composition. These crystals exhibit a unique rotating crystal lattice. The impact of such engineered crystal lattice on the structural environment of Er is determined. EBSD is used to characterize the lattice orientation, while EXAFS probes the local environment of erbium, as compared to stoichiometric and congruent Er:LiNbO₃.

The structural information is correlated with combined excitation emission spectroscopy to provide insight into the nature of the Er incorporation sites. Further, spectral hole burning and absorption measurements are used to understand how this structure affects relevant properties for a quantum memory. The potential for tuning laser processing parameters to optimize these properties is also discussed.