Subnatural-linewidth fluorescent single photons

Abstract: Subnatural-linewidth single photons are ofvital importance in quantum optics and quantum information science. According to previous research, it appears difficult to utilize resonance fluorescence to generate single photons with subnatural linewidth. Here we propose a universally applicable approach to generate fluorescent single photons with subnatural linewidth, which can be implemented based on {\Lambda}-shape and similar energy structures. Further, the general condition to obtain fluorescent single photons with subnatural linewidth is revealed. The single-photon linewidth can be easily manipulated over a broad range by external fields, which can be several orders ofmagnitude smaller than the natural linewidth. Our study can be easily implemented in various physical platforms with current experimental techniques and will significantly facilitate the research on the quantum nature of resonance fluorescence and the technologies in quantum information science.