Anisotropic exchange splitting in semiconductor quantum dots results in bright-exciton fine-structure splitting important for quantum information processing. Direct measurement of fine-structure splitting usually requires single/few quantum dots at liquid-helium temperature because of its sensitivity to quantum dot size and shape, whereas measuring and controlling fine-structure splitting at an ensemble level seem to be impossible unless all the dots are made to be nearly identical. Here we report strong bright-exciton fine-structure splitting up to 1.6 meV in solution-processed CsPbI₃ perovskite quantum dots, manifested as quantum beats in ensemble-level transient absorption at liquid-nitrogen to room temperature. The splitting is robust to quantum dot size and shape heterogeneity, and increases with decreasing temperature, pointing towards a mechanism associated with orthorhombic distortion of the perovskite lattice. Effective-mass-approximation calculations reveal an intrinsic ‘fine-structure gap’ that agrees well with the observed fine-structure splitting. This gap stems from an avoided crossing of bright excitons confined in orthorhombically distorted quantum dots that are bounded by the pseudocubic {100} family of planes.

半导体量子点中的各向异性交换分裂导致对量子信息处理很重要的亮激子精细结构分裂。精细结构分裂的直接测量通常需要液氦温度下的单个/几个量子点，因为它对量子点的大小和形状很敏感，而在整体水平上测量和控制精细结构分裂似乎是不可能的，除非所有的点被制成几乎相同。_{在这里，我们报告了在溶液处理的 CsPbI 3}中高达 1.6 meV 的强亮激子精细结构分裂钙钛矿量子点，在液氮至室温下表现为整体水平瞬态吸收的量子拍。分裂对量子点尺寸和形状异质性具有鲁棒性，并且随着温度的降低而增加，这表明与钙钛矿晶格的正交畸变相关的机制。有效质量近似计算揭示了与观察到的精细结构分裂非常吻合的内在“精细结构间隙”。这种差距源于避免了明亮激子的交叉，这些激子限制在正交扭曲的量子点中，这些量子点由赝立方 {100} 平面族为界。