Detection of Single Electron Charges in Nanoscale Dipoles and Anyon-Type Quantum Dots

In topological quantum computation, quantum information is encoded in a deco-herence free and fault-tolerant manner using exotic Majorana fermion quasiparticles. Recent advancements have revealed solid-state quantum dots hosting non-Abelian anyons, where a single electron contributes to the formation of a Majorana-bound vortex. This property makes them highly attractive for charge sensing applications. To evaluate charge sensing fidelity before detecting unit charges in candidate quantum dots, we fabricated and tested various nano-scale dipole structures consisting of two sub-20nm metal dots separated by a tunnel barrier. We experimentally demonstrate robust detection of single-electron switching within the various dipole structures using both single-electron transistors (SETs) and radio-frequency gate reflectometry. Single-electron switching detection within a dipole structure of this length scale has not been reported before. Additionally, we present a composite simulation frame-work combining COMSOL Multiphysics and SPICE to calculate the induced charge in the SET due to electron switching in the dipole, achieving excellent agreement with experimental results. Furthermore, we fabricated site-controlled non-Abelian anyon-type InP quantum dots and attempted spatial sensing of unit charges by positioning SETs in close proximity to the dots. However, our experimental observations are primarily attributed to substrate effects under light illumination. These findings highlight the necessity of carefully accounting for substrate effects in quantum dot experiments to ensure accurate and measurable outcomes.

在拓扑量子计算中，研究人员利用奇异的马约拉纳费米子准粒子（Majorana fermion quasiparticles）以无退相干且容错的方式编码量子信息。近期的研究进展发现，承载非阿贝尔任意子（non-Abelian anyons）的固态量子点中，单个电子参与了马约拉纳束缚涡旋（Majorana-bound vortex）的形成过程。这一特性使其在电荷传感领域极具应用潜力。为了在候选量子点中探测单电荷之前评估电荷传感保真度（charge sensing fidelity），我们制备并测试了多种纳米级偶极结构：该结构由两个被隧道势垒（tunnel barrier）分隔的尺寸小于20nm的金属量子点构成。我们通过实验证明，利用单电子晶体管（single-electron transistors, SETs）与射频栅极反射测量法（radio-frequency gate reflectometry），可在各类偶极结构中实现单电子开关（single-electron switching）的稳健探测。此前尚未有针对该尺度范围下偶极结构的单电子开关探测的相关报道。此外，我们提出了一种结合COMSOL多物理场仿真软件（COMSOL Multiphysics）与SPICE的复合仿真框架，用于计算偶极结构中电子开关效应在单电子晶体管中感应的电荷，该仿真结果与实验数据实现了极佳的吻合。进一步地，我们制备了位点可控的非阿贝尔任意子型磷化铟（InP）量子点，并尝试通过将单电子晶体管紧贴量子点放置，实现对单电荷的空间传感。但实验观测结果主要归因于光照条件下的衬底效应（substrate effects）。上述研究结果表明，在量子点实验中必须充分考虑衬底效应，才能确保实验结果的准确性与可测量性。