In the development of quantum technologies, quantum light sources capable of emitting single photons on demand play a crucial role. The realization of quantum light sources that operate at room temperature and function in the telecommunications wavelength range is essential for practical quantum technology applications such as quantum communication, quantum computing, and quantum sensing. Single-walled carbon nanotubes have attracted significant attention as quantum light sources in the telecommunications wavelength range due to their one-dimensional structure and excellent optical properties. Previous methods have faced difficulties in precisely managing quantum defect formation, particularly in accurately determining the number and position of defects.

In this study, we have developed a novel technique for deterministic creation of single organic color centers using *in-situ* photochemical reactions. Through real-time monitoring of photoluminescence spectra, we observed discrete intensity changes corresponding to individual color center formation, and achieved precise fabrication of single color centers by stopping the reaction upon detecting these changes. This technique enables position-selective formation of color centers, which we demonstrated through photoluminescence imaging. We also confirmed single-photon emission from the formed color centers through photon correlation measurements, establishing the quantum nature of the defects created by this technique.

This deterministic functionalization technique offers the potential for on-demand utilization of quantum defects with desired emission energies and demonstrates the capability to cover broader spectral ranges through the choice of chirality and molecular precursors. This level of precision paves the way for the development of atomically defined, scalable quantum photonic circuits operating at room temperature in the telecommunications wavelength range. This achievement is expected to represent a significant advance toward the realization of practical quantum technologies.

To learn more about this work, please refer to
D. Kozawa, Y. Shiota, M. Wang, Y. K. Kato Deterministic formation of single organic color centers in single-walled carbon nanotubes Nano Lett. 25, 13103 (2025).