Although the study of single quantum dot (QD) properties without the background noise and dephasing processes caused by surrounding carriers is a crucial issue, the spatial-selective excitation of a single QD is still challenging, due to the diffraction nature of light. Here, we demonstrate a deep subwavelength excitation of a single QD using two-photon plasmonic nanofocusing. Self-aligned plasmonic nanofocusing on a single QD was achieved using metal coated nanopyramid structures. The highly enhanced local electric field generated by the plasmonic nanofocusing gives rise to a large increase in the optical nonlinear effect (i.e., two-photon excitation). As a result of the enhanced field enhancement on the metal-pyramid hybrid structure, the two-photon luminescence intensity was enhanced by a factor of 5000, and the selective excitation of a single QD enabled us to observe InGaN QD emission at near room temperature, due to the large suppression of the background emission. Our approach opens promising perspectives for quantum optics experiments with highly reduced background emissions.

中文翻译：

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定点，两光子等离子纳米聚焦在单个量子点上，用于近室温操作

尽管在没有背景噪声和周围载流子引起的移相过程的情况下研究单量子点（QD）特性是一个关键问题，但是由于光的衍射特性，单个QD的空间选择性激发仍然具有挑战性。在这里，我们演示了使用双光子等离子体纳米聚焦的单个QD的深亚波长激发。使用金属涂层的纳米金字塔结构实现了对单个QD的自对准等离激元纳米聚焦。由等离子体纳米聚焦产生的高度增强的局部电场引起光学非线性效应（即，双光子激发）的大量增加。由于金属-金字塔杂化结构的场增强增强，双光子发光强度增强了5000倍，单个QD的选择性激发使我们能够在接近室温的情况下观察InGaN QD发射，这是由于对背景发射的抑制作用很大。我们的方法为大大降低背景发射的量子光学实验开辟了广阔的前景。