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.     

基于硅锗异质结的二维量子点阵列的制备与表征

硅基半导体量子点中的自旋量子比特近几年来发展迅速,其单比特门与两比特门操作保真度已经突破了容错量子计算的阈值.在此基础上,如何构建硅基量子点二维阵列变得广受学界关注,然而二维阵列复杂的结构在器件制备和测量上均带来挑战.本文设计并成功制备了一种Si/SiGe异质结上的2×4结构八量子点二维阵列器件.借助输运测量方法测量了八量子点器件的全部电荷稳定性相图,并进一步地使用电荷感应调制测量方法得到了器件内的少电子区电荷稳定性相图,说明了对量子点电荷态的高灵敏度探测能力.此外,通过调控势垒电极展示了对量子点间隧穿耦合的调控作用并测量了多量子点耦合的电荷稳定性相图.本文的研究结果展示了使用Si/SiGe异质结构建自旋量子比特二维阵列的潜力,为未来硅量子点二维阵列的进一步扩展提供经验与参考.