Cavity-enhanced two-photon source emitting narrow linewidth telecommunication wavelength photons for improved quantum memory-coupling efficiency enabling long-distance quantum communications

    Ryo Onozawa, Daisuke Yoshida, Kazuya Niizeki and Tomoyuki Horikiri

    Japanese Journal of Applied Physics, 61, 102008 (2022).

    • Photon source

    In long-distance quantum communication using quantum repeaters with quantum memories, entangled photons at telecommunication wavelengths that can be coupled to quantum memory with high efficiency are required. Typically, entangled photons are generated via spontaneous parametric down conversion (SPDC). However, the phase-matching bandwidth of SPDC is more than 100 GHz, which is much broader than the bandwidth of a Pr3+:Y2SiO5 quantum memory (with overall bandwidth of ∼10 GHz while the bandwidth of each frequency channel is ∼10 MHz) suitable for frequency-multiplexed quantum repeaters. In this study, nondegenerate SPDC (1550 nm and 995 nm) inside an optical cavity is used to obtain a narrow linewidth and cluster width of SPDC to match the Pr3+:Y2SiO5 bandwidth. We also developed a cavity control mechanism that can fulfill the doubly resonant condition. The developed two-photon source can maximize the coupling efficiency with Pr3+:Y2SiO5 by introducing wavelength conversion and is promising for use in a quantum repeater.

    Transfer of linewidth and frequency stability from an iodine-stabilized Nd: YAG laser to a quantum memory control laser through an optical frequency comb

    Takeshi Kondo, Seiho Shindo, Daisuke Yoshida, Yuma Goji, Mikitaka Nishihara, Taiki Aizawa, Feng-Lei Hong and Tomoyuki Horikiri

    Japanese Journal of Applied Physics, 61, 088003 (2022).

    • Interface

    To implement quantum repeaters for long-distance quantum communications, frequency stabilization is necessary for coupling telecommunication wavelength photons with quantum memories that operate in the visible region. Here, a narrow-linewidth optical frequency comb for frequency stabilization is developed through phase-locking to an iodine-stabilized Nd:YAG laser using high-speed servo control. Subsequently, we phase lock a Pr3+:Y2SiO5 (Pr:YSO) quantum memory control laser to the developed optical frequency comb for linewidth transfer. The obtained linewidth (3.1 kHz) and frequency stability (1.84 × 10−12 at an average time of 0.01 s) are sufficient for multimode storage in Pr:YSO quantum memory.

    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.