Cavity electro-optics in thin-film lithium niobate for microwave-to-optical transduction

Rare-earth ion-doped materials [1] with long optical coherence lifetimes can serve as frequency-multiplexed, long-lived optical quantum memories [2], which are of an essential requirement towards building frequency multiplexed quantum repeaters [3] for long-distance quantum communications. Towards this end, we investigate a thulium-doped crystal (Tm: YGG) [4, 5] at temperatures as low as 500 mK and low magnetic fields. This crystal offers an optical coherence lifetime exceeding one millisecond and a ground-state Zeeman level lifetime as long as tens of seconds. We take advantage of such exceptional features to show several key demonstrations; storage of optical pulses for up to 100 μs of optical storage time, frequency-multiplexed storage of 11 distinct frequency modes, a proof of principle demonstration of frequency-selective read-out of 3 distinct stored frequency modes. Our results suggest that Tm: YGG can be a potential candidate to be used as an optical quantum memory in frequency multiplexed quantum repeater architecture.