Long-distance entanglement distribution is a vital capability for quantum technologies. An outstanding practical milestone towards this aim is the identification of a suitable matter-photon interface that possesses, simultaneously, long coherence lifetimes and efficient telecommunication-band optical access. In this work we report upon the T center, a silicon defect with long-lived spins and spin-selective bound exciton optical transitions at 1326 nm in the telecommunications O-band. In this first study of T centers in 28 Si, we present the temperature dependence of the zero-phonon line, report ensemble zero-phonon linewidths as narrow as 33(2) MHz, and elucidate the excited state spectrum of the bound exciton. Magnetophotoluminescence, in conjunction with magnetic resonance, is used to observe twelve distinct orientational subsets of the T center, which are independently addressable due to the anisotropic g factor of the bound exciton's hole spin. Here we show that the T center in 28 Si offers electron and nuclear spin lifetimes beyond a millisecond and second, respectively, as well as optical lifetimes of 0.94(1) μs and a Debye-Waller factor of 0.23(1). This work represents a significant step towards coherent photonic interconnects between longlived silicon spins, spin-entangled telecom single-photon emitters, and spin-dependent silicon-integrated photonic nonlinearities for future global quantum technologies.

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Luminescence and optical absorption due to radiation damage centers in silicon has been studied exhaustively for decades, but is receiving new interest for applications as emitters for integrated silicon photonic technologies. While a variety of other optical transitions have been found to be much sharper in enriched 28 Si than in natural Si, due to the elimination of inhomogeneous isotopic broadening, this has not yet been investigated for radiation damage centers. We report results for the well-known G, W and C damage centers in highly enriched 28 Si, with optical linewidth improvements in some cases of over two orders of magnitude, revealing previously hidden fine structure in the G center emission and absorption. These results have direct implications for the linewidths to be expected from single center emission, even in natural Si, and for models for the G center structure. The advantages of 28 Si can be readily extended to the study of other radiation damage centers in Si. * thewalt@sfu.ca

*We study theoretically and experimentally coherent imaging of surface plasmon polaritons using either leakage radiation microscopy through a thin metal film or interference microscopy through a thick metal film. Using a rigorous modal formalism based on scalar Whittaker potentials we develop a systematic analytical and vectorial method adapted to the analysis of coherent imaging involving surface plasmon polaritons. The study includes geometrical aberrations due index mismatch which played an important role in the interpretation of recent experiments using leakage radiation microscopy. We compare our theory with experiments using classical or quantum near-field scanning optical microscopy probes and show that the approach leads to a full interpretation of the recorded optical images.