An atomic frequency comb memory in rare-earth doped thin-film lithium niobate

Atomic frequency comb memories that are compact and chip-integrated have broad applications in both classical and quantum information processing. Previously, atomic frequency comb memories have been achieved in rare-earth-doped ion diffused waveguides patterned in bulk lithium niobate. However, these devices have a large mode cross section which requires high optical power for coherent control and storage. Here we present a compact chip-integrated atomic frequency comb memory in rare-earth doped thin-film lithium niobate. We demonstrate both coherent control of the atomic ensemble and optical storage. Our optical memory exhibits a broad storage spectrum exceeding 100 MHz, and coherent optical storage time of over 250 ns. The strong light-matter interaction in our platform enables coherent rotations on the ions with a power that is three orders of magnitude smaller than previous results in large waveguides. We also take advantage of the thin film platform and fabricate impedance matched ring resonators using an optimized fabrication recipe to increase the storage efficiency. These results pave the way towards scalable, highly efficient, electro-optically tunable quantum photonic systems where one can store and manipulate light on chip with high bandwidth and low powers.