近日，瑞士苏黎世联邦理工学院的Gabriele Rainò&Maksym V. Kovalenko及其研究小组与美国混合有机-无机能源半导体中心的Peter C. Sercel等人合作并取得一项新进展。经过不懈努力，他们揭示单个卤化铯铅量子点中的单光子超辐射现象。相关研究成果已于2024年1月31日在国际权威学术期刊《自然》上发表。

该研究团队证实了钙钛矿量子点的单光子超辐射具有低于100皮秒的辐射衰减时间，几乎与已报道的激子相干时间一样短。辐射速率对量子点的大小、组成和温度的特征依赖表明，有效质量计算证实了巨大跃迁偶极子的形成。这一结果对于超亮相干量子光源的发展具有重要意义，并证明了量子效应，如单光子发射，在比激子玻尔半径大10倍的纳米粒子中仍然存在。

据悉，发射体的亮度最终由费米黄金法则来描述，辐射速率与它的振子强度乘以光子态的局部密度成正比。由于振子强度是材料固有的特性，因此，要实现更亮的发射，需要依赖光子态工程的局部密度，这可以通过使用介电或等离子体谐振器来实现。相比之下，另一个较少被探索的途径是利用一种被称为超辐射的集体行为来提高振子强度，进而提高发射率。最近，有人提出当后者的相干运动扩展到许多晶胞时，可以利用量子阱中弱约束激子的巨大振子强度跃迁来实现。

附：英文原文

Title: Single-photon superradiance in individual caesium lead halide quantum dots

Author: Zhu, Chenglian, Boehme, Simon C., Feld, Leon G., Moskalenko, Anastasiia, Dirin, Dmitry N., Mahrt, Rainer F., Stferle, Thilo, Bodnarchuk, Maryna I., Efros, Alexander L., Sercel, Peter C., Kovalenko, Maksym V., Raino, Gabriele

Issue&Volume: 2024-01-31

Abstract: The brightness of an emitter is ultimately described by Fermi’s golden rule, with a radiative rate proportional to its oscillator strength times the local density of photonic states. As the oscillator strength is an intrinsic material property, the quest for ever brighter emission has relied on the local density of photonic states engineering, using dielectric or plasmonic resonators. By contrast, a much less explored avenue is to boost the oscillator strength, and hence the emission rate, using a collective behaviour termed superradiance. Recently, it was proposed that the latter can be realized using the giant oscillator-strength transitions of a weakly confined exciton in a quantum well when its coherent motion extends over many unit cells. Here we demonstrate single-photon superradiance in perovskite quantum dots with a sub-100 picosecond radiative decay time, almost as short as the reported exciton coherence time. The characteristic dependence of radiative rates on the size, composition and temperature of the quantum dot suggests the formation of giant transition dipoles, as confirmed by effective-mass calculations. The results aid in the development of ultrabright, coherent quantum light sources and attest that quantum effects, for example, single-photon emission, persist in nanoparticles ten times larger than the exciton Bohr radius.

DOI: 10.1038/s41586-023-07001-8

Source: https://www.nature.com/articles/s41586-023-07001-8