Professor Yeom Dong-il's Team Develops First Quantum Entangled Light Source In Optical Communication Band Based On 2D Material-Fiber Device

A research team led by Professor Dong-il Yeom (Department of Physics, Department of Energy Systems Engineering) at Ajou University, in collaboration with a research team from the Korea Research Institute of Standards and Science, has succeeded in developing a communication-band optical fiber quantum entanglement light source based on 2D van der Waals materials. The newly developed optical fiber-based quantum light source can be directly connected to existing optical communication networks, and is expected to become a core foundation for next-generation quantum communication, quantum sensors, and quantum computing technologies.

Quantum communication and quantum computing use 'photons' as the basic units for transmitting information. In particular, quantum entanglement, in which two photons share a single quantum state, is a key resource that enables quantum cryptography, which is fundamentally impossible to hack, and distributed quantum computing, which is necessary for heat generation and error correction.

Conventional quantum entanglement light sources have disadvantages such as being bulky, requiring very sensitive optical alignment, and having high coupling loss with optical fiber-based communication networks. Additionally, quantum entanglement light sources generated within the optical fiber itself have been proposed, but there have been practical limitations, such as the need for long optical fiber lengths and difficulties in securing high-quality, noise-free quantum states.

To overcome this, the research team proposed an optical device in which a novel van der Waals material (SnP₂S₆) with very strong second-order nonlinear optical properties is directly coupled to an optical fiber. The SnP₂S₆ material utilized by the researchers exhibits prominent near-infrared nonlinear optical signals even at a thickness of several micrometers (μm, 1/1000 mm), enabling the world's first report of entangled photon pairs in the commercial optical communication standard band (1,550 nanometers (nm)) using an optical fiber device coupled with this material. This is attracting attention for presenting the potential for next-generation optical fiber quantum devices that are easy to connect with existing optical communication networks and operate stably without the need for separate, complex optical alignment.

The developed device also demonstrated excellent performance in performance measurements. The 'CAR (Coincidence-to-Accidental Ratio)' value, which indicates the purity and quality of the generated photons, showed performance 100 times superior to existing 2D material-based light sources. In addition, through tomography technology to measure quantum states, the generated photons recorded a maximum 'Fidelity' and 'Purity' of 0.97 (closer to 1 indicates complete entanglement), verifying the formation of a high-quality polarization quantum entanglement state.

"Professor Yeom Dong-il stated, 'Research is underway to improve device performance so that it can be applied to various actual systems, and it is expected to be utilized in diverse quantum technology fields in the future, such as quantum cryptography, quantum sensors, and distributed quantum computers.'"

In this study, Professor Dong-il Yeom and Researcher Joong-seok Choi of Ajou University participated as the corresponding author and first author, respectively, while Dr. Sang-min Lee, Dr. Hee-soo Park, and Dr. Sung-joo Ha of the Korea Research Institute of Standards and Science participated as co-corresponding authors and co-first authors. The research was published online in July in 'Advanced Science,' a world-renowned journal in the field of materials science, and was supported by the National Research Foundation of Korea's Follow-up Program for Basic Research Laboratories, the Support Program for Mid-Career Researchers, and the Korea Institute of Information and Communication Technology Planning and Evaluation's Quantum Science & Technology Flagship Project.