Our research group is dedicated to establishing innovative device platform technologies that will enable future networks and next-generation computing. We also strive to develop and implement advanced applied technologies that drive the creation of new business opportunities in the fields of measurement, computation, and communications. Focusing on optical waveguide device technologies--particularly silica-based planar lightwave circuits (PLC) and periodically poled lithium niobate (PPLN) waveguides--we are advancing research and development aimed at surpassing conventional performance limitations. Through these efforts, we seek to achieve groundbreaking optical devices that bring transformative innovations to the information and communication technology (ICT) society.

・Optical devices for an ultra-fast optical quantum computer

【 Press Release 】
・October 1, 2015　 NOTICE REGARDING THE STATUS AND CONCLUSION OF STOCK REPURCHASES (UNDER THE PROVISIONS OF NTT'S ARTICLES OF INCORPORATION PURSUANT TO PARAGRAPH 2, ARTICLE 165 OF THE COMPANIES ACT OF JAPAN)
・November 5, 2019　 NTT and JAXA Launch Joint Research for Ultra‑High‑Speed, Large‑Capacity, and Secure Optical/Wireless Communication Infrastructure Seamlessly Connecting Earth and Space
・September 30, 2021　 100,000-spin coherent Ising machine ～High-speed solution search for large-scale combinatorial optimization problems enabled with a large-scale optical computer～
・December 22, 2021　 Realization of modularized quantum light source toward fault-tolerant large-scale universal optical quantum computers
・March 6, 2023　 43-GHz real-time optical quantum signal detection for ultrafast quantum computation Toward super quantum computers with optical high-speed communication technologies
・June 16, 2023.　 Successful Long‑Distance Lumped Optical Parametric Amplification Relay Transmission over the World's Largest 14.1 THz Bandwidth - Expected to Expand Wavelength Resources for All‑Photonic Networks in IOWN/6G
・September 3, 2024　 World's first long-haul optical inline-amplified transmission over 100 Tbit/s capacity using ultra long-wavelength band conversion Toward IOWN/6G, single-core optical fiber capacity more than three times larger than current technology
・November 8, 2024　 Realizing a New Paradigm in Quantum Computing - World's First General-Purpose Optical Quantum Computing Platform Launched
・April 25, 2025　 Successful Demonstration of Basic Technology Enabling On-Demand, Timely APN Connections from Any Location in IOWN APN

【 NTT Technical Review 】
・March 2019　 Ultra‑High‑Speed Communication Technology Supporting Future High‑Capacity Communication Infrastructure - Low‑Noise, High‑Power Parametric Amplification Relay Technology
・June 2022　 Device Technology Realizing Next-Generation Computing Using Light: Continuous-Wave, Broadband Squeezed Light Source for High-Speed Optical Quantum Computers
・January 2021　 Media Robotics as the Boundary Connecting Real Space and Cyberspace: Visible-Light Planar Lightwave Circuit Technology and Integrated Laser-Light-Source Module for Smart Glasses

・Technology

Optical quantum computers use the rules of quantum mechanics to perform calculations, with the potential to solve certain problems much faster than conventional computers. Because of this promise, research and development in this field is highly competitive around the world. Among various approaches to quantum computing, the method that uses photons--particles of light--has several important advantages. One key benefit of optical quantum computers is that they do not need special equipment like cryogenic (extremely cold) or vacuum systems, which are often required in other types of quantum computers. This makes it easier to construct system that are smaller and more practical. Also, by creating continuously generated entangled photons, it is possible to increase the number of qubits (quantum bits) without needing to add many more physical components. In addition, the wide bandwidth of light allows for very fast processing. This approach also works well with existing optical communication technologies, meaning that the low-loss optical fibers and advanced photonic devices used in telecommunications can also be used here. These features make optical quantum computers strong candidates for real-world use. However, there are still challenges. One major issue is the difficulty of generating squeezed light, which is an important quantum resource for optical quantum computers. So far, there are no high-performance, fiber-coupled quantum light sources that operate in the telecom wavelength range. Also, many high-speed optical communication devices cannot be used as-is in quantum systems. For example, regular fast photodetectors often cause too much optical loss, which destroys the fragile quantum states. Because of this, earlier systems had to use specially designed, low-loss detectors that were much slower, limiting the speed of the computer. To solve these problems, we are developing fiber-coupled quantum light sources that work at telecom wavelengths, and optical parametric amplifiers that can boost quantum signals without destroying them. With these technologies, we aim to bring ultra-fast optical communication techniques into the field of optical quantum computing.

・Features

In optical quantum computers, squeezed light plays a key role as a source of quantum properties. Squeezed light is a special state of light where the quantum uncertainty (or quantum noise) in one of a pair of non-commuting physical quantities is reduced below the standard quantum limit. It consists of even-numbered photon streams and has reduced quantum noise, making it an essential resource for generating entangled quantum states. This special property--called photon number parity--also enables quantum error correction. By taking advantage of the fact that the squeezed light consists of an even number of photons, certain types of errors can be detected and corrected. For this reason, squeezed light is also very important in the development of quantum error correction techniques. However, producing squeezed light is technically difficult, and the quantum state can easily degrade due to optical losses. So far, there has been no practical source of squeezed light that works in the telecom wavelength range, maintains the wide bandwidth of light, and achieves a high squeezing level. Our research focuses on solving this problem by using periodically poled lithium niobate (PPLN) waveguides. These waveguides offer strong nonlinear optical effects and low loss--both of which are essential for generating squeezed light efficiently. Utilizing these properties, we are developing high-performance quantum light sources that can meet the demands of future optical quantum technologies.

・Application

By using optical communication devices, it is possible to build a stable, maintenance-free, and closed system for optical quantum computing. This approach allows the development of practical-scale optical quantum computers and marks a major step toward achieving functional, real-world quantum machines. In the system shown in the diagram, the first module generates squeezed light, while the second module uses an optical parametric amplifier (OPA) to convert quantum information carried by light into classical optical signals. Unlike the conventional balanced homodyne detection method, this measurement technique can amplify and convert quantum signals directly into classical optical signals without destroying the light, making it possible to perform measurements at significantly higher speeds. This technology is also applicable to the development of future all-optical quantum computers, which operate entirely using light. It can contribute significantly to the realization of ultra-fast quantum computers running at terahertz clock frequencies, opening the path to a new era of high-speed quantum processing.