The Silicon Vacancy in Silicon Carbide: a promising qubit in a technological material

一个电子存储器能缩小到多小？存储的极限可以通过将信息编码在单个粒子中来达到，例如单个电子或单个原子核。有几种方法可以将一位信息编码成电子，例如，可以将粒子的存在标记为“1”，将粒子的不存在标记为“0”。或者，人们可以使用量子物体的一种称为“自旋”的内在属性，这使得粒子表现得像一个微小的磁铁。在这种情况下，例如，“1”将被编码为指向北极的自旋，而“0”将被编码为指向单粒子磁体的南极的自旋。使用单个粒子来编码信息可以带来超越小型化的优势。电子自旋服从量子力学定律。在量子物理学中，电子的自旋不需要像磁针一样指向“北”或“南”，但它可以同时指向“北”和“南”。或者，当计算设备中的比特处于“0”或“1”状态时，量子比特可以同时处于两者。这不仅仅是一个奇怪的好奇心：在过去的几十年里，我们已经了解到量子力学定律可以用来完成经典物理学无法完成的任务，例如安全通信，更快的计算或精确的传感。这个项目的目标是测量和控制碳化硅中的单自旋，碳化硅是一种由硅和碳原子组成的晶格材料。这种晶格中缺少的硅原子会产生一个缺陷，该缺陷包含一个可以通过激光和射频脉冲测量和操纵的单个电子自旋。基本上，该系统表现为被困在碳化硅中的单个原子。为什么选择碳化硅？除了承载具有良好性能的自旋之外，碳化硅是半导体工业常规用于制造晶体管和其他微电子元件的技术材料。现有的生长、掺杂和纳米制造方法可以使量子器件实用化，但碳化硅中的单自旋控制仍处于起步阶段。我们直到最近才知道电子在这些缺陷中是如何排列的。仅在去年，碳化硅中的单次旋转控制才得以展示。我们可以通过了解这些缺陷的结构来提高控制工具的效率。本项目将通过研究这些缺陷如何吸收和发射光来表征它们的电子结构。通过在非常低的温度下工作，与原子振动有关的噪声将被冻结掉，而这些噪声会掩盖光信号。关于光发射和吸收的知识，以及它与缺陷中捕获的自旋的关系，将使我们能够实现令人兴奋的计划，使用单自旋来编码和解码未来技术的信息。

How small can one shrink an electronic memory? The ultimate limit in storage can be reached by encoding information in a single particle, for example a single electron or a single atomic nucleus. There are several ways to encode a bit of information into an electron. For example, one could label "1" the presence of the particle, and "0" its absence. Or, one could use an intrinsic property of quantum objects called "spin", which makes the particle behave as a tiny magnet. In this case, "1" would be encoded, for example, as spin pointing to the North Pole and "0" as spin pointing to the South Pole of the single particle magnet. Using single particles to encode information can give advantages that go beyond miniaturization. Electron spins obeys the laws of quantum mechanics. In quantum physics, the spin of an electron is not required to point either "North" or "South", like a magnetic needle, but it can be "North" AND "South" at the same time. Or, while a bit in a computing device is either in the "0" or "1" state, a quantum bit can be both at the same time. This is much more than a bizarre curiosity: in the last few decades, we have learnt that the laws of quantum mechanics can be exploited to perform tasks impossible for classical physics, such as secure communication, faster computing or precise sensing.The goal of this project is to measure and control single spins in silicon carbide, a material consisting of a lattice of silicon and carbon atoms. A silicon atom missing in this lattice creates a defect which hosts a single electronic spin that can be measured and manipulated by laser and radiofrequency pulses. Basically, this system behaves as a single atom trapped in silicon carbide. Why silicon carbide? In addition to hosting spins with great properties, silicon carbide is a technological material routinely used by the semiconductor industry to manufacture transistors and other microelectronic components. The availability of established recipes for growth, doping and nano-fabrication can lead to practical quantum devices.Control of single spins in silicon carbide is still in its infancy. We learned only recently how electrons are arranged in these defects. Only in the past year, control of a single spin in silicon carbide was demonstrated. There is plenty of information missing, and we can improve the efficiency of our control tools by learning more about the structure of these defects.This project will characterize the electronic structure of these defects by studying how they absorb and emit light. By operating at very low temperatures, the noise related to atomic vibrations which would mask the optical signal will be frozen out. The knowledge about light emission and absorption, and its relation to the spin trapped in the defect, will enable us to realizing exciting schemes that use single spins to encode and decode information for future technologies.