We investigate the single photon scattering by an emitter chirally coupled to a one-dimensional waveguide. The single-photon transport property is essentially different from the symmetrical coupling case. The single photons propagating towards the emitter in opposite directions show different transmission behaviors, which is a manifestation of the single-photon diode. In the ideal chiral coupling case, the transmission probability of the single photon transport in one direction is zero by critical coupling, while in the opposite direction it is unity. The diode works well only when the single-photon frequency meets certain conditions. For a two-level emitter, the diode works well when the single photon is nearly resonant to the emitter. For a $Λ$-type three-level emitter, when the single-photon frequency is greatly altered, we can adjust the parameters of the external laser to ensure the diode works well. The latter provides a manner to realize a single-photon switch, in which the single-photon transmission probability can reach zero or unity although the emitter's decay is considered.
Hunan Key Laboratory for Micro-Nano Energy Materials and Devices and School of Physics and Optoelectronics, Xiangtan University（湘潭大学物理与光电工程学院）；Department of Electronic Science, College of Big Data and Information Engineering, Guizhou University（贵州大学大数据与信息工程学院电子科学系）
A single-mode external cavity diode laser using an intra-cavity atomic Faraday filter with short-term linewidth $<400$ kHz and long-term stability of $<1$ MHz
