Optical observation of nuclear spin states of a single ion

稀土离子在无机晶体中的核自旋是一种用于处理量子信息的固态体系。为了利用RE离子构建单个自旋量子位元的集成系统，必须对核自旋进行单独检测和控制。然而，只有少数实验成功地解决了固体中单个稀土离子的核自旋态。利用显微装置对单个离子进行光致发光检测的主要障碍是离子的弱发射和整个晶体的背景发射。解决方案之一是使用比焦点体积小的晶体。在这里，我们采取了不同的方法来开发一个单组分非球面反射物镜。由于焦体积小，立体角大，SN比提高到单离子水平。

Nuclear spin of rare-earth (RE) ion doped in an inorganic crystal is a solid-state system useful for processing quantum information. In order to utilize RE ions to build an integrated system of an individual spin qubits, the nuclear spins must be individually detected and controlled. However, only a few experiments were successful in resolving nuclear spin states of single RE ion in solid. The major obstacles in photo-luminescence detection of a single ion with a microscopic setup are weak emission of the ion and background emission from the whole crystal. One of the solutions is to use a crystal smaller than the focal volume. Here we took a different approach to develop a single-component aspheric reflecting objective. Owing to a larger solid-angle of a smaller focal volume, the SN ratio improved to a single-ion level.