Optical linewidth narrowing for device-coupled single T centers

Single T centers in silicon are highly promising for quantum networking due to their telecom-band optical transitions and long spin coherence times. However, when integrated into nanophotonic devices, these centers exhibit broad optical linewidths—often two orders of magnitude larger than their radiative limit—due to spectral diffusion caused by a fluctuating local charge environment. This broadening significantly hinders the performance of quantum repeaters and other quantum information applications.

The researchers utilized a laser scanning microscope to deliver both resonant (1326 nm) and above-band (980 nm) optical excitation to single T centers coupled to photonic crystal cavities. By applying pulsed above-band excitation, they aimed to generate free carriers that fill nearby charge traps, effectively neutralizing the local electric field noise. They systematically characterized the resulting linewidth narrowing and center frequency shifts using time-resolved photoluminescence excitation (PLE) spectroscopy.

The study reports a 70% reduction in the optical linewidth of single T centers, confirming that above-band excitation effectively stabilizes the local charge environment. The researchers observed that this narrowing effect requires photon energies exceeding the silicon bandgap, supporting the mechanism of free-carrier-induced trap filling. Furthermore, they developed a rate-equation model that successfully describes the charge stabilization dynamics and explains the observed center frequency shifts. The stabilization is shown to be persistent in the dark for over 300 microseconds, though it is gradually diminished by the resonant laser used for measurement.

This work provides a practical, scalable method to suppress spectral diffusion in solid-state quantum emitters. By demonstrating that simple above-band optical control can significantly improve the optical coherence of T centers, this study removes a critical barrier to the development of high-fidelity quantum networking platforms based on silicon-integrated spin systems.