Bright Telecom Spin-Photon Interface in Silicon Photonics

Silicon-based quantum photonics is limited by the lack of efficient, bright, and optically addressable spin qubits that operate in the telecom band. While the T-center is a known candidate, its relatively long excited-state lifetime and sensitivity to thermal depopulation constrain its photon emission rate and coherence. This paper investigates the Al1-center, an aluminum-carbon defect, as a superior alternative for integrated quantum networks.

The authors synthesized Al1-centers using sequential carbon and aluminum ion implantation into silicon-on-insulator (SOI) nanophotonic devices. They employed tapered nanobeam waveguides to enhance light collection and performed a comprehensive suite of optical characterizations, including time-resolved photoluminescence, second-order autocorrelation, and two-tone resonant photoluminescence excitation spectroscopy. To evaluate the spin properties, they utilized magneto-optical spectroscopy under external magnetic fields up to 9 T.

The Al1-center demonstrates exceptional performance as a quantum emitter. It exhibits high-purity single-photon emission with a $g^{(2)}(0)$ of 0.04 and a fast excited-state lifetime of 135 ns, which is nearly an order of magnitude faster than the T-center. The authors resolved a homogeneous linewidth of 47 MHz, which is three times narrower than the T-center under similar conditions, indicating superior optical coherence. Furthermore, magneto-optical measurements confirmed the presence of a spin-1/2 ground state and demonstrated spin-selective optical pumping, a critical requirement for quantum state initialization and readout.

By combining high brightness with a stable spin ground state in the telecom S-band, the Al1-center addresses a major bottleneck in silicon quantum photonics. Its faster transition dynamics and improved spectral properties make it a highly promising candidate for scalable, integrated quantum networks and distributed quantum computing architectures that leverage existing silicon foundry infrastructure.