Atomic lenses and ideal single-photon detections

Photon detector is one of the key units in the integrated optical devices. Due to the weak atom-photon interaction, the detection efficiency of a single photon by a bare atom (as a photon detector aside the waveguide) is relatively low (the most reachable value is shown as $50%$, which has being approached experimentally). In order to overcome such a limit, a pair of spatially separated two-level atoms (the photon lenses) with adjustable inflection and transmission coefficients of the photon are introduced to generate an atomic cavity, in which the detected probability of the waveguide photon by the single detector can be significantly enhanced (even reach to $100%$ under certain conditions). The proposal is demonstrated specifically by a circuit QED system for highly effective detection of a single microwave photon.