多能级冷原子系统中五阶光学非线性增强的理论和实验研究

As is well known, optical nonlinearities play important roles in the area of quantum optics and quantum information science. This program aims to realize the enhancement of the fifth-order nonlinearity with suppressed linear and nonlinear absorptions in cold atoms experimentally. First we should set up a platform for sensitive measurment of the fifth-order susceptibility using the cavity transmission spectrum. Since the fifth-order susceptibility will be greatly enhanced by the atomic coherence in the homogeneously broadened medium, set up the MOT platform for atom cooling and trapping is necessary. According to the foregoing theoretical research,a chain-N six-level system and a tripod five-level system of the cold Rb atom will be configured to realize fifth-order susceptibility enhancement. An amplitude comparable to the Kerr nonlinear susceptibility in a simple three-level system is expected to be achieved experimentally, which can be used to produce efficient three-way entanglement, realize three-qubit quantum phase gates, and so on. On the other hand, we will further explore new schemes and dynamics for the enhancement of fifth-order nonlinearity.

高阶光学非线性效应在量子光学和量子信息领域有着非常重要的作用。本项目拟开展多能级冷原子系统中五阶光学非线性效应增强的理论和实验研究。采用腔透射谱法，探讨精确测量五阶非线性系数的实验方法并建立相应的实验平台；根据现有的两种增强五阶非线性系数的理论方案，搭建冷原子系统，实验测量出增强的五阶非线性系数；在理论模拟指导下，优化实验参数，使增强的五阶非线性可在单光子水平下实现π相移，为基于五阶非线性的混频效率提高、三比特量子相位门构建提供实验依据。在此过程中，结合我们前期在三阶非线性增强方面的研究基础，进一步探索弱场下五阶非线性增强的理论新方案和物理新机制。

介质光学非线性的增强和操控是非线性光学、量子光学等的重要研究课题。原子介质作为量子光学基础实验的最常用介质，其光学非线性的增强和测量至关重要。本项目主要开展了多能级冷原子和室温铷原子系统中三阶和五阶非线性效应的有效测量和增强研究。一方面，建立了测量三阶和五阶非线性系数的实验平台、搭建了冷原子系统、实验测量了多个能级体系的三阶和五阶非线性系数；另一方面，利用搭建好的实验平台，开展了M型五能级系统中暗态偶极子的观测、光学腔衰荡光谱的研究以及验证了冷原子与光学腔集体强耦合条件下的光学互易传输特性。