The coherent interaction of electromagnetic fields with solid-state two-level systems can yield deterministic quantum light sources for photonic quantum technologies. To date, the performance of semiconductor single-photon sources based on three-level systems is limited mainly due to a lack of high photon indistinguishability. Here we tailor the cavity-enhanced spontaneous emission from a ladder-type three-level system in a single epitaxial quantum dot through stimulated emission. After populating the biexciton (XX) of the quantum dot through two-photon resonant excitation, we use another laser pulse to selectively depopulate the XX state into an exciton (X) state with a predefined polarization. The stimulated XX–X emission modifies the X decay dynamics and improves the characteristics of a polarized single-photon source, such as a source brightness of 0.030(2), a single-photon purity of 0.998(1) and an indistinguishability of 0.926(4). Our method can be readily applied to existing quantum dot single-photon sources and expands the capabilities of three-level systems for advanced quantum photonic functionalities.

电磁场与固态两能级系统的相干相互作用可以产生用于光子量子技术的确定性量子光源。迄今为止，基于三能级系统的半导体单光子源的性能受到限制，主要是由于缺乏高光子不可区分性。在这里，我们通过受激发射在单个外延量子点中定制来自梯型三能级系统的腔增强自发发射。在通过双光子共振激发填充量子点的双激子 (XX) 后，我们使用另一个激光脉冲将 XX 状态选择性地减少到具有预定义极化的激子 (X) 状态。受激的 XX-X 发射改变了 X 衰变动力学并改善了偏振单光子源的特性，例如0.030（2）的源亮度，0.998（1）的单光子纯度和0.926（4）的不可区分性。我们的方法可以很容易地应用于现有的量子点单光子源，并扩展了高级量子光子功能的三能级系统的能力。