The quantum internet promises to revolutionize the way we communicate, compute, and secure data by harnessing the fundamental properties of light particles known as photons. Central to this ambitious vision is the ability to manipulate single photons and their delicate quantum states efficiently and reliably. Researchers at Tohoku University have made a groundbreaking advancement by developing a sophisticated photonic router capable of directing both individual and entangled photons with remarkable precision and minimal loss. This innovation draws us significantly closer to realizing practical quantum networks and next-generation photonic devices that could transform global communications infrastructure.
At the heart of the quantum internet’s potential is the photon, the elementary particle of light, which acts as a carrier of quantum information. Photons can encode quantum bits, or qubits, using their polarization—essentially the orientation of their electromagnetic waves. However, directing photons along a network without degrading their quantum information has been a persistent challenge. Previous devices struggled to maintain polarization integrity at the wavelengths commonly used in telecommunications, often introducing unacceptable loss or noise. The novel photonic router introduced by Professor Fumihiro Kaneda’s team addresses this problem head-on by offering a solution that preserves photon polarization with fidelity above 99%, all while operating with unprecedented low optical loss.
This quantum router utilizes an ingeniously redesigned interferometer, departing from conventional rectangular path designs in favor of a parallelogram arrangement. This subtle yet critical structural innovation allows optical components to preserve photon polarization by enabling operation at nearly normal angles of incidence. Such meticulous engineering minimizes detrimental effects like polarization rotation or decoherence that could otherwise disrupt the quantum signal. By maintaining strict polarization control, the router ensures that quantum information encoded in the photons remains intact during passage, a prerequisite for secure quantum communication and quantum computing networks.
The device excels not only in preserving polarization but also achieves extraordinary optical efficiency by minimizing the number of components in the signaling pathway. Every optical interface introduces some degree of loss, which, at the quantum scale, can critically limit performance. The Tohoku University team’s router transmits photons with a loss as small as 0.06 dB—equivalent to just a 1.3% loss rate. This figure places the technology in a league markedly superior to most existing photonic routing mechanisms. Such efficiency enables photon signal transmission at speeds measured in nanoseconds, suitable for real-time quantum data processing and compatible with current telecommunications infrastructure.
Crucially, this innovative device is engineered to function at telecom wavelengths, the standard spectral bands used in today’s fiber optic internet networks. Compatibility with existing infrastructure is paramount for the deployment of quantum communication technologies on a global scale. By aligning their design with these widely used wavelength bands, Kaneda’s photonic router offers a seamless upgrade pathway toward integrating quantum networks with the classical internet backbone, thereby facilitating scalable and practical quantum data transmission.
Beyond the routing of single photons, the researchers have demonstrated a world-first capability to route two-photon entangled states using the device. Quantum entanglement—the counterintuitive linkage between separate quantum particles—underpins many advanced quantum technologies, including quantum sensing and distributed quantum networks. Successfully routing entangled photons while maintaining interference visibility near 97% signals the device’s ability to handle complex quantum states without compromising entanglement quality, a major milestone for scalable quantum networks.
The precision and stability of the photonic router also reflect a reduction in noise and distortion, issues that plague many previous quantum photonic devices. The team’s approach optimizes the router’s internal architecture to mitigate spurious scattering and other disruptive phenomena that can degrade quantum signal coherence. Consequently, the system maintains not only the integrity of quantum information but also ensures rapid, noise-free operation, qualities essential for real-world quantum technologies.
This pioneering photonic router sets a new benchmark for quantum device performance by fulfilling all critical criteria—low loss, high speed, faithful polarization maintenance, and compatibility with telecom fibers—within a single compact and robust apparatus. Such multifunctional integration is rare in quantum photonics, where devices often excel in one area but compromise in others. The Tohoku University invention effectively bridges these gaps, enabling the practical deployment of quantum communication systems that can coexist with and enhance today’s internet infrastructure.
At a fundamental level, this achievement leverages electro-optic control techniques that can dynamically steer photons through different output ports with high precision. The electro-optic effect allows the device to manipulate the photon’s path in nanoseconds, facilitating fast, deterministic routing of quantum signals. This dynamic control capability is vital for future quantum networks where routing decisions must adapt rapidly to complex communication protocols or computational requirements.
The ramifications of this photonic router extend beyond communication, as efficient and reliable photon manipulation advances numerous fields reliant on photonic quantum technologies. This includes quantum computing architectures that utilize photonic qubits, quantum metrology systems benefiting from entanglement-enhanced measurements, and secure quantum cryptographic schemes demanding high-fidelity quantum state preservation during transmission.
Professor Kaneda underscores the significance of this advancement, emphasizing that the system avoids the pitfalls of degraded quantum signals—akin to a “broken telephone” scenario where information becomes distorted along the way. By ensuring that transmitted photon polarization matches the original signal with exceptional accuracy, the router instills confidence that quantum information will remain trustworthy and usable throughout intricate quantum networks.
In summary, the development of this low-loss, polarization-maintaining photonic router represents a pivotal step toward the materialization of the quantum internet. By meeting the stringent requirements for practical operation, including interfacing with existing telecommunication fibers, preserving quantum coherence, and enabling high-speed routing, this device lays the groundwork for the next era of quantum communication and quantum-enhanced technologies. Ongoing research and further optimization promise to push these boundaries even further, heralding a future where quantum networks become integral to everyday life.
Subject of Research: Quantum photonic routing and quantum communication technology
Article Title: Low-loss polarization-maintaining router for single and entangled photons at a telecom wavelength
News Publication Date: 2-Sep-2025
Web References:
http://dx.doi.org/10.1002/qute.202500355
Image Credits: ©Pengfei Wang et al.
Keywords
Photons, Computational science, Quantum computing, Computer science, Quantum mechanics, Quantum entanglement
