1.Center for Quantum Sciences, School of Physics, Northeast Normal University, Changchun 130024, China 2.Hunan Key Laboratory of Super Microstructure and Ultrafast Process, School of Physics and Electronics, Central South University, Changsha 410083, China
Abstract:In recent years, it has been a hot research topic to study the interaction between atomic ensemble and cavities, and many researches have been done in this regard. In such a system, some atoms are trapped in the cavity, which can be used to study their dynamic characteristics, e.g., the evolution of photon numbers and photon transition. The Jaynes-Cummings model is an important model for studying the dynamic characteristics of the cavity-atom system, which is based on the interaction between a single two-level atom and the cavity field. Recently, coherent photon control in cavity under specific conditions has become an important part of quantum computing and communication. It is worth noting that the tunable photon transmission and all-optical switches based on the cavity have already aroused much interest and have been used in many areas. The quantum information and networks are mostly rooted in complex optical devices, which may show nonreciprocal or asymmetric photon transport. In this paper, we demonstrate that by using an optical closed-loop system the unconventional photon transport can be realized with two mutually perpendicular cavities coupled through external fiber and a two-level atom placed on the intersection. This three-mode system supports two orthogonal propagation directions, that is to say, and the interactions among probe fields are mutually perpendicular. Without ignoring the spontaneous decay of the natural atom, the complex and controllable quantum interference induced by the efficient hybrid interaction of the light, cavity modes, and the atom in such a closed-loop structure can result in a few interesting symmetric and asymmetric photon transport behaviors, i.e. coherent perfect synthesis and coherent perfect reflection. Aside from these compelling properties, the group velocity can also be modulated, i.e., fast and slow light effect. All of these processes can be dynamically controlled by using the probe field phase difference, the tunneling coupling between two cavities and the coupling between the cavity and the atom. Importantly, due to so many advantages, such a tunable scheme can be readily extended to some optical devices, e.g., the switch and the router that is challenging to conventional optical devices. Keywords:cavity-atom system/ quantum interference/ controllable photon transport
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2.模型和方程如图1(a)所示, 考虑了一个腔-原子闭环的三模系统, 双腔的模分别为a和b, 双腔分别与二能级原子耦合, 二能级原子的基态(激发)态为$\left| g \right\rangle $($\left| e \right\rangle $). 如图1(b)所示, 将两个法布里-珀罗微腔相互垂直, 将原子放置于十字相交处, 并且考虑两腔完全相同的理想情况, 即腔本征频率、衰减率以及腔原子耦合系数相同[19,43], 从而构造对称的系统结构. 类似的结构已用于研究PT-对称非线性光学[44]. 此外, 通过微波电路将腔与原子耦合机制[45,46], 也可实现两腔同频率、同衰减率. 之所以使用垂直结构, 是由于对于光腔中大部分沿轴向运动的光子来说, 两腔垂直放置可以减少两腔中光子之间的相互作用, 从而避免两腔在与原子耦合时同时出现额外的不可控相互作用. 而系统在两个光腔通过外部的光纤进行可控的耦合, 从而实现可控的量子干涉现象. 图 1 (a)由两个光学腔模和原子组成的闭环三模系统图; (b)正交腔结构的装置图 Figure1. (a) Schematic diagram of an optical system composed of two optical cavities and the atomic ensemble; (b) realistic setup of that optical system with the double-cavity orthogonal structure.