Gurioli Massimo, Wang Zhiming, Rastelli Armando, Kuroda Takashi, Sanguinetti Stefano
University of Firenze, Firenze, Italy.
Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu, China.
Nat Mater. 2019 Aug;18(8):799-810. doi: 10.1038/s41563-019-0355-y. Epub 2019 May 13.
The long dreamed 'quantum internet' would consist of a network of quantum nodes (solid-state or atomic systems) linked by flying qubits, naturally based on photons, travelling over long distances at the speed of light, with negligible decoherence. A key component is a light source, able to provide single or entangled photon pairs. Among the different platforms, semiconductor quantum dots (QDs) are very attractive, as they can be integrated with other photonic and electronic components in miniaturized chips. In the early 1990s two approaches were developed to synthetize self-assembled epitaxial semiconductor QDs, or 'artificial atoms'-namely, the Stranski-Krastanov (SK) and the droplet epitaxy (DE) methods. Because of its robustness and simplicity, the SK method became the workhorse to achieve several breakthroughs in both fundamental and technological areas. The need for specific emission wavelengths or structural and optical properties has nevertheless motivated further research on the DE method and its more recent development, local droplet etching (LDE), as complementary routes to obtain high-quality semiconductor nanostructures. The recent reports on the generation of highly entangled photon pairs, combined with good photon indistinguishability, suggest that DE and LDE QDs may complement (and sometimes even outperform) conventional SK InGaAs QDs as quantum emitters. We present here a critical survey of the state of the art of DE and LDE, highlighting the advantages and weaknesses, the achievements and challenges that are still open, in view of applications in quantum communication and technology.
长期以来梦寐以求的“量子互联网”将由量子节点（固态或原子系统）网络组成，这些节点由飞行量子比特连接，自然是以光子为基础，以光速长距离传播，退相干可忽略不计。一个关键组件是光源，能够提供单光子对或纠缠光子对。在不同的平台中，半导体量子点（QD）非常有吸引力，因为它们可以与其他光子和电子组件集成在小型化芯片中。20世纪90年代初，开发了两种方法来合成自组装外延半导体量子点，即“人造原子”——也就是斯特兰斯基-克拉斯坦诺夫（SK）方法和液滴外延（DE）方法。由于其稳健性和简单性，SK方法成为在基础和技术领域取得多项突破的主力方法。然而，对特定发射波长或结构及光学特性的需求促使人们进一步研究DE方法及其最新发展——局部液滴蚀刻（LDE），作为获得高质量半导体纳米结构的补充途径。最近关于产生高度纠缠光子对以及良好光子不可区分性的报道表明，作为量子发射器，DE和LDE量子点可能补充（有时甚至优于）传统的SK铟镓砷量子点。我们在此对DE和LDE的现状进行批判性综述，鉴于其在量子通信和技术中的应用，突出其优点和缺点、已取得的成就以及仍未解决的挑战。
