Coupling of a quantum memory and telecommunication wavelength photons for high-rate entanglement distribution in quantum repeaters

    Kyoko Mannami, Takeshi Kondo, Tomoki Tsuno, Takuto Miyashita, Daisuke Yoshida, Ko Ito, Kazuya Niizeki, Ippei Nakamura, Feng-Lei Hong, and Tomoyuki Horikiri

    Optics Express, 29, 41522-41533 (2021).

    • Memory

    • Interface

    Quantum repeaters are indispensable tools for long-distance quantum communication. However, frequency matching between entangled photon sources and remote quantum memories (QMs) is difficult, which is an obstacle to the implementation of quantum repeaters. In this paper, we demonstrate a method to achieve the coupling of a Pr:YSO as a fixed-time QM with a single telecommunication-wavelength photon through frequency stabilization using an optical frequency comb over all applied laser wavelengths. The demonstrated method can lead to the implementation of a quantum repeater scheme enabling an improvement of the entanglement generation rate, paving the way for long-distance quantum communication.

    Offset-locking-based frequency stabilization of external cavity diode lasers for long-distance quantum communication

    Takuto Miyashita, Takeshi Kondo, Kohei Ikeda, Kazumichi Yoshii, Feng-Lei Hong and Tomoyuki Horikiri

    Japanese Journal of Applied Physics, 60, 122001 (2021).

    • Interface

    Quantum repeaters are required for long-distance quantum communication. For efficient coupling of quantum entangled photon sources with narrow-linewidth quantum memories, we performed the frequency stabilization of two lasers at 1514 and 1010 nm. The 1514 nm pump laser of the entangled photon source exhibited a frequency stability of  3.6 × 10–12(τ = 1 s).The 1010 nm pump laser of the wavelength conversion system exhibited a frequency stability of 3.4 × 10–12(τ = 1 s).The stabilities of both lasers were approximately two orders of magnitude smaller than the frequency width of 4 MHz of the Pr:YSO quantum memory. Such frequency-stabilized lasers can realize the remote coupling of a quantum memory and an entangled photon source in quantum repeaters.

    Entanglement distribution between quantum repeater nodes with an absorptive type memory

    Daisuke Yoshida, Kazuya Niizeki, Shuhei Tamura, and Tomoyuki Horikiri

    International Journal of Quantum Information,18, 2050026 (2020).

    • Memory

    Quantum repeaters, which are indispensable for long-distance quantum communication, are necessary for extending the entanglement from short distance to long distance; however, high-rate entanglement distribution, even between adjacent repeater nodes, has not been realized. In a recent work by [C. Jones et al., New J. Phys. 18 (2016) 083015], the entanglement distribution rate between adjacent repeater nodes was calculated for a plurality of quantum dots, nitrogen-vacancy centers in diamond, and trapped ions adopted as quantum memories inside the repeater nodes. Considering practical use, arranging a plurality of quantum memories becomes so difficult with the state-of-the art technology. It is desirable that high-rate entanglement distribution is realized with as few memory crystals as possible. Here, we propose new entanglement distribution scheme with one quantum memory based on the atomic frequency comb which enables temporal multimode operation with one crystal. The adopted absorptive-type quantum memory degrades the difficulty of multimode operation compared with the previously investigated quantum memories directly generating spin-photon entanglement. It is shown that this scheme improves the distribution rate by nearly two orders of magnitude compared with the result in [C. Jones et al., New J. Phys. 18(2016)083015] and the experimental implementation is close by utilizing state-of-the-art technology.