We use two-photon excitation to create biexcitonic complexes with two electron-hole pairs in different orbital levels of a GaAs/AlAs quantum dot. In addition to $p$-shell emission of the biexcitonic triplet states generated by two-photon excitation, we observe additional higher-energy resonances which are a signature of the radiative cascade of two-photon excited singlet states. The detection of these signals obtained in a high excitation regime is made possible by the use of a waveguiding structure in which the quantum dots are inserted, allowing an orthogonal excitation and detection geometry with an excellent laser rejection.

中文翻译：

---

在 GaAs/AlAs 量子点中使用双光子激发揭示两个电子-空穴对配合物的自旋单重态

我们使用双光子激发在 GaAs/AlAs 量子点的不同轨道能级中创建具有两个电子-空穴对的双激子复合物。此外$p$-由双光子激发产生的双激子三重态的壳层发射，我们观察到额外的高能共振，这是双光子激发单重态辐射级联的特征。通过使用插入了量子点的波导结构，可以检测在高激发状态下获得的这些信号，从而允许正交激发和检测几何结构具有出色的激光抑制。