Broadband optical nonreciprocity in an N-type thermal atomic system

Abstract

Nonreciprocal propagation of light plays a very important role and attracts a great deal of research interest in quantum optics and quantum information sciences for the intriguing physics and the vast prospective applications. In order to enhance the nonreciprocal bandwidth of light, we investigate nonreciprocal propagation of the weak probe field by controlling two strong control fields in a cavity-free N-type thermal Rb87 atomic system. From the theoretical analysis, it is found that, the linewidth of the EIT windows and thus the nonreciprocal bandwidth for the probe field are mainly determined by the intensities of the control fields Ω1 and Ω2. For proper Ω1, nonreciprocal bandwidth of the probe field can be significantly enhanced by increasing Ω2, which implies the probability of generating more than 100 MHz bandwidth for optical nonreciprocity. The principle experimental demonstration in the Rb87 thermal atomic system is consistent with the theoretical analysis, and we obtain ∼60 MHz nonreciprocal bandwidth in experiments. Our work may provide references for all-optical nonreciprocal quantum devices such as optical isolator, circulator and router in optical information processing.