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arXiv:2108.13130 · Japanese Journal of Applied Physics

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, Tomoyuki Horikiri

Published Oct 11, 2021• 13 citations
arXivHTMLPDF

Abstract

Abstract 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.

DOI
10.35848/1347-4065/ac2e67

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Abstract 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.
Abstract 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 Pr 3+ :Y 2 SiO 5 (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.
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. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
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.
Abstract 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 Pr 3+ :Y 2 SiO 5 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 Pr 3+ :Y 2 SiO 5 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 Pr 3+ :Y 2 SiO 5 by introducing wavelength conversion and is promising for use in a quantum repeater.
We developed a frequency-stable laser light source operating at 436 nm to produce entangled photon pairs at 606 nm and 1.5 µm via spontaneous parametric down conversion. This light source was produced via the sum frequency generation of two lasers operating at 852 and 895 nm, each stabilized to the D2 and D1 transitions of cesium atoms, respectively. We evaluated the frequency stability of the light source using heterodyne measurements between two identical setups. The developed light source can be used to generate frequency-stable photon pairs, a critical requirement for quantum repeaters using Pr:YSO quantum memories.
Abstract We propose a scheme to phase lock a quantum-memory control laser, frequency-conversion pump laser, and two-photon source over three octaves in frequency to operate a quantum memory. The absolute frequencies of the laser sources are determined based on a Doppler-free iodine hyperfine transition. The achieved relative frequency instability and uncertainty were ≤1 × 10–12 and 3 × 10–11, respectively, which are below the requirement for operating a Pr:YSO quantum memory. This scheme simplifies the instrumentation of laser sources in a quantum repeater, and increases the reliability of quantum communication systems.