石墨烯纳米机械振子和门控量子点的耦合研究

Nanomechanical resonators are considered as interfaces between different physical systems. How to construct phonon-based data bus attracted significant interests in quantum information devices researches. Recently, coupling between nanomechanical resonators, nanomechanical resonator and superconducting microwave cavity, and many other systems have reached strong coupling regime. How to construct highly controllable interaction system, consisting of nanomechanical resonators and electrons, is an important topic. This project aims to construct a coupling system between nanomechanical resonators and gate-defined quantum dot in suspended bilayer graphene, based on our previous results. We will design and improve sample structure and measuring scheme, to detect charge state and spin state of gate-defined double quantum dot via nanomechanical resonator at ultralow temperature. And we will extract coupling strengths under different conditions, and try to use quantum dot to cool the resonator. This project will contribute to construction of novel quantum devices, and exploration of several important questions in quantum computation, including how to detect state of electrons efficiently, what kind of role phonon played in dephasing of gate-defined quantum dot based qubit, and how to construct novel data bus.

纳米机械振子被视作各个不同物理系统之间的接口，利用其中的声子态构造数据总线在量子信息器件研究中吸引了广泛关注。当前，纳米机械振子与纳米机械振子，超导微波腔等体系的耦合已达到强耦合区域，如何构造高度可控的纳米机械振子中的声子和电子的相互作用体系是重要的研究课题。本项目计划在已有的诸项相关研究成果基础上，以悬浮的双层石墨烯纳米结构为研究对象，构造门控量子点，纳米机械振子及其耦合体系，设计优化样品结构及测量方案，在极低温下利用机械振子对门控双量子点的电荷态和自旋态进行探测，提取不同条件下的耦合强度，尝试用量子点对振子进行冷却。该项目的实施将有助于构造新型量子器件，探索量子计算需求解决的如何高效探测电子的状态，声子在门控量子点量子比特的退相干机制中扮演何种角色，如何构造新型数据总线等问题。

如何利用固态体系实现高度可控，可扩展的量子比特及其耦合架构是目前量子计算研究的热点和重点。半导体门控量子点是实现这一架构的热门量子比特体系候选，纳米机械振子是实现扩展架构的可选方案之一。本项目开展了纳米机械振子与半导体门控量子点相互作用的研究，设计制备了门控量子点和纳米机械振子的复合结构；实现了非近邻耦合的石墨烯纳米机械振子声学模式二能级的相干时域操纵；观测到了石墨烯纳米机械振子随栅极调制的频率环，并给出了和实验可以很好吻合的滑动模型；设计制备了纳米声子晶体结构。以上结果对于探索和降低纳米机械振子的耗散，拓展纳米机械振子的调控方式，和实现以机械振动为媒介的量子比特扩展架构有重要意义。