基于重叠栅工艺的硅量子点阵列的制备与调控

利用半导体量子点阵列结构实现近邻耦合是规模化扩展自旋量子比特的主要方案之一. 随着量子点数目的增加, 量子点阵列器件的制作工艺及参数调控均愈加复杂. 本文介绍了一种重叠栅工艺结构, 利用多层相互重叠且具有不同功能的栅极定义量子点, 制作出结构紧凑、 调控性好的量子点阵列器件, 解决了工艺扩展的难题. 此外,本文发展了一套高效可靠的调控方法, 按顺序逐个添加量子点并建立虚拟电极, 实现了对量子点参数的独立控制,并且能够高效且独立地调控各量子点中的电子数目, 克服了大规模量子点阵列中电压参数配置的困难. 这些方法为未来实现大规模自旋比特阵列提供了一种标准化的方案.     

Qubits based on semiconductor quantum dots

Semiconductor quantum dots are promising hosts for qubits to build a quantum processor. In the last twenty years, intensive researches have been carried out and diverse kinds of qubits based on different types of semiconductor quantum dots were developed. Recent advances prove high fidelity single and two qubit gates, and even prototype quantum algorithms.These breakthroughs motivate further research on realizing a fault tolerant quantum computer. In this paper we review the main principles of various semiconductor quantum dot based qubits and the latest associated experimental results. Finally the future trends of those qubits will be discussed.     

Electron States in Parallel Double Quantum Dots with a Tunable Inter-Dot Coupling

We study the electron states on lateral double quantum dots coupled in parallel. The charge stability diagrams are given in terms of the gate voltages of both dots. We discover that the two electron states translate from separated states to coupled states continuously by increasing the inter-dot coupling strength. Our results demonstrate that the parallel-quantum-dot tunability bodes well for future quantum computing applications.     

Spin manipulation in semiconductor quantum dots qubit

Thirty years of effort in semiconductor quantum dots has resulted in significant developments in the control of spin quantum bits(qubits). The natural two-energy level of spin states provides a path toward quantum information processing. In particular, the experimental implementation of spin control with high fidelity provides the possibility of realizing quantum computing. In this review, we will discuss the basic elements of spin qubits in semiconductor quantum dots and summarize some important experiments that have demonstrated the direct manipulation of spin states with an applied electric field and/or magnetic field. The results of recent experiments on spin qubits reveal a bright future for quantum information processing.     

Probing Energy Spectrum of Quadruple Quantum Dots with Microwave Field

A double quantum dot defines a qubit by a two-level system. The coupling between two qubits induces a double two-level system into a four-level system. We study experimentally the coupling between two capacitive coupled GaAs/AlGaAs double quantum dots while tuning the energy detuning of each double quantum dot simultaneously. Applying microwave photons （at a frequency of 20 GHz） on this system and observing the resonance tunneling with a quantum point contact detector, we obtain an excitation spectrum which is consistent with the numerical simuIation result of a coupled two-qubit Hamiltonian. This study demonstrates that a double quantum dot can be exploited as an extraordinary platform for controlled quantum gates.     

Charge noise acting on graphene double quantum dots in circuit quantum electrodynamics architecture

We investigate the dephasing mechanisms induced by the charge noise and microwave heating effect acting on a graphene double quantum dot(DQD) capacitively coupled to a microwave resonator. The charge noise is obtained from DC transport current, and its contribution to dephasing is simultaneously determined by the amplitude response of the microwave resonator. A lowfrequency 1/f-type noise is demonstrated to be the dominant factor of the dephasing of graphene DQD. Furthermore, when the applied microwave power is larger than-90 d Bm, the dephasing rate of graphene DQD increases rapidly with the increase of microwave power, and fluctuates slightly with the applied microwave power smaller than-90 d Bm. Our results can be applied to suppress the impeditive influence on the dephasing of graphene-based devices associated with microwave input in the perspective investigations.     

基于应变锗空穴双量子点的可调耦合和自旋阻塞研究

应变锗空穴量子点是实现超大规模量子计算最有前景的平台之一.由于锗空穴不受超精细相互作影响，有着较长的自旋弛豫时间和量子退相干时间，且锗中本征的强旋轨道耦合和空穴载流子的低有效质量，使得全电场操控空穴自旋量子比特得以实现，极大地降低了器件加工难度，增加了量子点的可扩展性.本文介绍了一种使用应变锗异质结制备重叠栅空穴双量子点器件的方法，完成了应变锗异质结性质测量，空穴双量子点器件制作，单量子点输运性质和双量子点输运性质研究，双量子点耦合可研究调节性研究，以及外磁场存在下的漏电流性质研究和泡利自旋阻塞解除机制的研究.这些工作为未来实现高质量自旋量子比特制备和高保真度量子逻辑门操控提供了实验平台和基本参数.