Coherent Optical Memory Based on a Laser-Written On-Chip Waveguide

Quantum memory is the core device for the construction of large-scale quantum networks. For scalable and convenient practical applications, integrated optical memories, especially on-chip optical memories, are crucial requirements because they can be easily integrated with other on-chip devices. Here, we report the coherent optical memory based on a type-IV waveguide fabricated on the surface of a rare-earth iondoped crystal (i.e., Eu3+:Y2SiO5). The properties of the optical transition (F-7(0) -> D-5(0)) of the Eu3+ ions inside the surface waveguide are well preserved compared to those of the bulk crystal. Spin-wave atomic frequency comb storage is demonstrated inside the type-IV waveguide. The reliability of this device is confirmed by the high interference visibility of 97 +/- 1% between the retrieval pulse and the reference pulse. The developed on-chip optical memory paves the way towards integrated quantum nodes.