Nonreciprocity in Cold Atoms Based on Electromagnetically Induced Transparency

Nonreciprocal quantum devices with low loss are indispensable in quantum information processing but challenging to be realized. Here we report an experiment to realize the nonreciprocal phase shift larger than rr with low loss in a cavity-free and magnetic-free cold atomic ensemble based on electromagneti-cally induced transparency. Furthermore, a four-port all-optical circulator is demonstrated with an average isolation ratio of 22.25 dB and transmission of 0.94 for each channel. At its optimal working point, the circulator's total isolation ratio reaches 63.47 dB, transmission reaches 0.86, and fidelity at about 0.99. Our work can advance further investigation of nonreciprocity with cold atoms in quantum information processing applications.