Quantum memories with long storage times are key elements in long-distance quantum networks. The atomic frequency comb (AFC) memory in particular has shown great promise to fulfill this role, having demonstrated multimode capacity and spin-photon quantum correlations. However, the memory storage times have so-far been limited to about one millisecond, realized in a Eu3+ doped Y2SiO5 crystal at zero applied magnetic field. Motivated by studies showing increased spin coherence times under applied magnetic field, we developed a AFC spin-wave memory utilizing a weak 15 mT magnetic field in a specific direction that allows efficient optical and spin manipulation for AFC memory operations. With this field configuration the AFC spin-wave storage time increased to 40 ms using a simple spin-echo sequence. Furthermore, by applying dynamical decoupling techniques the spin-wave coherence time reaches 530 ms, a 300-fold increase with respect to previous AFC spin-wave storage experiments. This result paves the way towards long duration storage of quantum information in solid-state ensemble memories.
@article{arxiv.1910.08009,
title = {Optical storage for 0.53 seconds in a solid-state atomic frequency comb memory using dynamical decoupling},
author = {Adrian Holzäpfel and Jean Etesse and Krzysztof T. Kaczmarek and Alexey Tiranov and Nicolas Gisin and Mikael Afzelius},
journal= {arXiv preprint arXiv:1910.08009},
year = {2021}
}