On-demand storing time-bin qubit states with optical quantum memory

Quantum memory, serving as a crucial device for storing and releasing quantum states, holds significant importance in long-distance quantum communications. To date, quantum memories have been realized in many different systems. However, most of them have complex structures and high cost. Besides, it is not easy to simultaneously achieve both high storage efficiency and fidelity. In this paper, we experimentally demonstrate a low-cost optical quantum memory with high efficiency and high fidelity, by utilizing a butterfly-shaped cavity consisting of one polarization beam splitter, two reflecting mirrors, and one pockels cell crystal. In order to quantify the quality of the quantum memory, we carry out tomography measurements on the time-bin qubits encoded with weak coherent states after storage for N rounds. The storage efficiency per round can reach up to 95.0%, and the overall state fidelity can exceed 99.1%. It thus seems very promising for practical implementation in quantum communication and networks.