Crystal-based waveguide quantum memories

Quantum memories are devices that can store photonic quantum information and release it after a controlled time. Quantum repeaters can be constructed based on optical quantum memories to overcome the exponential decay of the signal during transmission when the communication distance increases, thus realizing large-scale quantum networks. As a promising candidate for quantum memories, bulk rare-earth-ion-doped crystals have been widely utilized in quantum memory experiments. Similar to the course of development of classical memories, quantum memories are also heading towards miniaturization and integration. This paper will describe one of the most promising technical routes to construct crystal-based waveguide quantum memories in bulk rare-earth-doped crystal by using femtosecond laser micromachining techniques.