Single-shot high-resolution identification of discrete frequency modes of single-photon-level optical pulses

    Daisuke Yoshida, Mayuka Ichihara, Takeshi Kondo, Feng-Lei Hong, and Tomoyuki Horikiri

    Physical Review A, 106, 052602 (2022).

    • Interface

    • Memory

    Frequency-multiplexed quantum communication usually requires a single-shot identification of the frequency mode of a single photon. In this paper, we propose a scheme that can identify the frequency mode with high resolution even for spontaneously emitted photons whose generation time is unknown, by combining the time-to-space and frequency-to-time mode mapping. We also demonstrate the mapping of the frequency mode (100 MHz intervals) to the temporal mode (435 ns intervals) for weak coherent pulses using atomic frequency combs. This frequency interval is close to the minimum frequency mode interval of the atomic frequency comb quantum memory with the Pr3+-ion-doped Y2SiO5 crystal, and the proposed scheme has the potential to maximize the frequency multiplexing of the quantum repeater scheme with the memory.

    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.