LQUOM Inc. (Yokohama, Japan) recently submitted an academic article entitled “Space-division multiplexed phase compensation for quantum communication: concept and field demonstration” by Riku Maruyama et al. The manuscript is now available on arXiv.
[Title] Space-division multiplexed phase compensation for quantum communication: concept and field demonstration
[Authors] Riku Maruyama1,2, Daisuke Yoshida1,2, Koji Nagano1, Kouyou Kuramitani1, Hideyo Tsurusawa1, and Tomoyuki Horikiri1,2
[Affiliations] 1 LQUOM Inc., 2 Yokohama National University
Quantum communication is expected to realize unique applications of quantum cryptography, distributed quantum computation, and quantum sensor networks. Distance limitation remains a fundamental problem in quantum communication because a single photon is lost in a long-distance fiber channel. Phase-sensitive quantum communication with a single-photon interference scheme receives intensive attention for extending the quantum communication distance. A single-photon interference scheme measures the phase information of the photon after transmitting through an optical fiber channel. Thus, the phase drift in the fiber directly leads to a communication error. The phase compensation of the optical fiber remains a central problem in the field demonstration of quantum communication with a single-photon interference scheme.
Our article demonstrates “space-division” multiplexed phase compensation as a novel category of phase compensation techniques. We conceptualize our space-division multiplexed phase compensation by using two neighboring fibers, one for quantum communication and the other for real-time sensing and compensating for the phase drift. Our phase compensation scheme solely depends on the tight correlation of the phase drifts between the two fibers. However, little is known about the phase drift correlation between the two fibers in a field environment. Here, we demonstrate the space-division multiplexed phase compensation in the Osaka metropolitan area network.
We have measured the phase drifts of two neighboring fibers for over ten days. Our field investigation has confirmed the phase drift correlation between the two fibers. Thanks to this correlation, the differential between the fibers significantly reduces the phase drift in the field fibers. We evaluate the impact of our phase compensation on quantum communication by calculating the quantum bit error rate (QBER) from the experimental phase data. As expected, our space-division multiplexed phase compensation significantly improves the QBER. We have also tested the robustness of our phase compensation system in the field on a weekly scale. These results validate space-division multiplexed phase compensation in a field environment, even in a metropolitan area.
[Impacts of this study]
Our phase compensation scheme is compatible with any single-photon interference schemes, including twin-field quantum key distribution and a quantum repeater with the DLCZ scheme. In addition, our phase compensation system can be extended to the phase compensation of multiple fibers in parallel without multiplying the number of phase compensation systems. The system scalability is a unique advantage of our phase compensation scheme and will help the future commercial deployment of the quantum communication schemes with a single-photon interference. In conclusion, our present study has demonstrated space-division multiplexed phase compensation for quantum communication. Our space-division multiplexed scheme can be combined with the existing technologies of time- and wavelength-division multiplexed phase compensation. We expect that our technology will broaden the opportunities for the field deployment of long-distance quantum communication.
The authors thank Yoshitaro Tsuji, Motoki Tanaka, Soichiro Nishiuma, and Takaaki Yui (OPTAGE Inc.) for arranging the field fiber experiment and Mahoro Yoshida for supporting our project. This research was supported by Deep-Tech Startups Support Program (New Energy and Industrial Technology Development Organization, Japan).