串联耦合三量子点的电荷稳态研究

Charge stability diagram of serial triple quantum dots

串联耦合三量子点(serial triple quantum dots,STQD)体系在近十年来受到人们的广.关注,这不仅是提高量子点集成度的一个必然过程,更重要的是可以利用STQD中一些特定的电荷占据态来实现自旋量子比特的快速全电学调控.本文运用常相互作用模型,导出了与外部可观测物理量相关的STQD电化学势,借助数值模拟计算得到STQD在不同中间栅电压下的线性输运二维电荷稳态图(简称二维稳态图),着重研究STQD的各种电荷占据态之间的能量简并点(简称能量简并点),结合实验将STQD中的能量简并点归纳为三种类型,对这些能量简并点的深入理解可以指导实验高效地寻找STQD体系中适合量子计算的工作区.

Serial triple quantum dot(STQD) systems have received extensive attention in the past decade,not only because quantum dot scaling up is an indispensable ingredient for integrations,but also due to the fact that specific charge states of STQD can be employed to achieve fast full-electrical manipulation of spin qubits.For the latter,a comprehensive understanding of the relationship between neighboring charge occupancy states of STQD is essential for three-electron exchange-only spin qubit-based quantum computations.Charge stability diagram is usually employed to map out the charge occupation states about the plunger gate voltages of STQDs and to study the degeneracy among charge occupation states.Experimentally,two-rather than threedimensional charge stability diagram was obtained in a lot of early studies by keeping one of plunger gates unchanged to reduce complexity.The obtained two-dimensional diagram can only provide limited information and is subject to blurred boundary of charge occupation states due to the low tunneling current and the energy level broading effects.It is,therefore,challenge to searching for the working points where quantum manipulation can be performed promptly and accurately.In principle,three-dimensional charge occupation stability diagram can be efficiently constructed by numerical simulations based on constant interaction(CI) model.In this study,we calculate the electrochemical potential of STQD about three plunger gate voltages by using the CI model-based capacitance network to reproduce any desired two-dimensional charge stability diagram.The simulated diagram not only well accords with the diagrams obtained from the early experimental data of STQD,but also provides high clarity of the charge state boundaries with tunable parameters.The systematical study of two-dimensional charge stability diagram reviews the energy degeneracy triple and quadruple points of STQD charge occupation states and concludes the energy degeneracy points in three types to compare with experimental data.For each of the energy degeneracy points,we discuss both the electron and hole transport by using the electrochemical potential alignment schematics.We reveal the common and unique triple points of STQD in comparison with those of double quantum dot.The quadruple points of STQD are also addressed in the manipulation of quantum cellular automata and quantum logical gate.The comprehensive understanding of these energy degeneracy points can efficiently guide experiments to build an optimal working point of the STQD system for quantum computations and simulations.