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系统。为了利用稀土离子建立单个自旋量子比特的集成系统，必须对核自旋进行单独的探测和控制。然而，只有少数实验成功地解决了固体中单一稀土离子的核自旋态问题。单个离子在微观结构下的光致发光检测的主要障碍是离子的微弱发射和整个晶体的本底发射。其中一种解决方案是使用比焦体积小的晶体。在这里，我们采取了一种不同的方法来研制一种单分量非球面反射镜。由于较大的立体角和较小的焦体积，信噪比提高到了单离子水平。

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.