Researchers at Tohoku University have made significant strides toward realizing the quantum internet with the development of a groundbreaking photonic router. This new technology can direct single and entangled photons with exceptional efficiency, a crucial advancement for the future of quantum networks. The findings, published in the journal Advanced Quantum Technologies on September 2, 2025, herald a new era for quantum communication and computing.
The quantum internet offers the potential for enhanced speed and security compared to existing systems. Central to this vision are photons, the fundamental particles of light that enable a range of quantum applications, from secure communications to advanced quantum computing. For these technologies to become practical, photons must be routed swiftly and reliably, while preserving their delicate quantum states.
One of the key challenges in this field has been the effective routing of photons encoded with arbitrary polarization at telecom wavelengths. Polarization is a common method for encoding quantum information, but previous devices often struggled with issues such as high optical loss and inadequate fidelity. The research team, led by Professor Fumihiro Kaneda, has addressed these challenges by creating a novel electro-optic router.
Innovative Design Enhances Performance
The new router incorporates a unique design featuring a compact interferometer where the optical paths form a parallelogram. This configuration allows for polarization-maintaining operation of all optical components at nearly normal angles of incidence. According to Professor Kaneda, “It shouldn’t be like a game of broken telephone where information gets lost along the way. Essentially, our design makes it so that the signal received is as close as possible to the signal that was sent – photon polarization was preserved with over 99% fidelity.”
The router boasts an impressive performance, transmitting photons with only 0.06 dB of loss, which translates to approximately 1.3%. This remarkable efficiency operates at nanosecond speeds and is compatible with existing telecommunication networks, making it a practical solution for future quantum technologies. Professor Kaneda emphasized that these advancements lay a solid foundation for developing viable quantum network technologies.
In a world-first demonstration, the team successfully routed two-photon entangled states, which are essential for quantum sensing and networking. They achieved an interference visibility of about 97%, showcasing the router’s capability to manage not only individual quantum bits but also complex multiphoton entanglements. This feature is vital for scaling up quantum technologies.
Meeting the Demands of Future Technologies
The new device stands out compared to previous approaches that often faced significant limitations, such as high loss, noise, or distortion. By combining low loss, high speed, and noise-free operation with compatibility for existing telecom fiber networks, this router meets all the critical requirements necessary for practical applications.
The work of the Tohoku University team, including researchers Pengfei Wang, Soyoung Baek, Masahiro Yabuno, Shigehito Miki, and Hirotaka Terai, represents a pivotal step in the pursuit of quantum internet technologies. As the field of quantum optics continues to evolve, innovations like this photonic router may soon transform the way we connect and communicate online, paving the way for a more secure and efficient digital future.
