Perfect non-reciprocal reflection amplification in closed loop coherent gain atomic system

High performance non-reciprocal photonic devices can improve the efficiency of optical quantum manipulation, information processing, and quantum simulation effectively. The enhanced optical signal can simultaneously amplify the weak signal output by the quantum system and isolate the sensitive quantum system from the back-scattered external noise, which is the core technology of high-performance photonic devices. In our previous work (Opt. Express 31, 38228), we have achieved dynamic control of unidirectional reflection amplification based on four-wave mixing gain and utilizing the linear variation of coupling field intensity with position. In this article, we ingeniously design a simple three-level closed loop coherent gain atomic system, innovatively setting the intensity of coupling field varying with position by step shape to break the spatial symmetry of probe susceptibility, and achieving perfect non-reciprocal reflection amplification. In contrast, the stepped variation of coupling field intensity is easier to adjust in experiments, this can reduce the difficulty in the experiment greatly. Specifically, the system introduces phase modulation. By changing the phase, the frequency region of probe gain and absorption can be switched, which makes the modulation of reflection amplification more flexible.