Optical spin readout of a silicon color center in the telecom L-band

Abstract: Silicon-based quantum technologies have gained increasing attention due to their potential for large-scale photonic integration, long spin coherence times, and compatibility with CMOS fabrication. Efficient spin-photon interfaces are crucial for quantum networks, enabling entanglement distribution and information transfer over long distances. While several optically active quantum emitters in silicon have been investigated, no spin-active defect with optical transitions in the telecom L-band-a key wavelength range for low-loss fiber-based communication-has been experimentally demonstrated. Here, we demonstrate the optical detection of spin states in the C center, a carbon-oxygen defect in silicon that exhibits a zero-phonon line at 1571 nm. By combining optical excitation with microwave driving, we achieve optically detected magnetic resonance, enabling spin-state readout via telecom-band optical transitions. These findings provide experimental validation of recent theoretical predictions and mark a significant step toward integrating spin-based quantum functionalities into silicon photonic platforms, paving the way for scalable quantum communication and memory applications in the telecom L-band.