Cavity-coupled qubits in diamond for networked quantum computing

宽带隙材料中的点缺陷，如金刚石中的氮空位(NV)中心，在未来的量子信息技术中显示出强大的量子比特(Qbit)潜力。它们的关键特征之一是相干光学接口，它允许量子信息在静态的电子和核自旋态与飞行的光子之间传输，并促进它们在量子通信系统中的使用，以及为可扩展的量子处理器构建网络。然而，近年来一个重要的瓶颈是这种自旋-光子界面的低效率(~1%)，这限制了可伸缩性，从而限制了这种方法所取得的影响。应对这一挑战的研究工作集中在探索新的颜色中心和将NV中心集成到光学微腔中。该项目将调查基于单片Fabry Perot设计的新型微腔的使用，类似于通过外延技术生长的垂直腔面发射激光器等半导体器件中广泛使用的微腔。金刚石不支持异质外延生长，所以腔镜将被溅射的介质(商业上可以买到的)沉积在金刚石薄膜的两侧。学生将开发形成薄膜的技术，以实现具有高品质因数的稳定腔模式，这是增强相干自旋-光子耦合强度所必需的。这将涉及表面图案化以制造微透镜结构，使用东道主部门提供的聚焦离子束研磨和光刻等技术。关键的品质因数将是控制表面的形状，作为确定模式几何形状的手段，以及表面粗糙度，该表面粗糙度确定受散射损失限制的最大镜面反射率。这些参数将分别使用光学轮廓术和原子力显微镜进行测量。学生将使用腔模式的光学光谱学来表征所得到的腔设备，该设备存在于东道主研究小组内。该项目的目标是在项目结束时实现珀塞尔因子为50的腔模，这将有望转化为约70%的接口效率。该项目属于EPSRC量子技术研究领域，该研究小组是英国量子计算和模拟中心的一部分。通过这项计划，该项目将与供应高规格合成钻石的英国公司Element Six Ltd和提供定制钻石蚀刻能力的牛津仪器等离子技术公司合作。还计划成立一家开发钻石量子技术的衍生公司，如果实现，将与该项目对接，并将成为该项目成果商业化的潜在途径。

Point defects in wide band gap materials, such as the nitrogen vacancy (NV) centre in diamond, show strong potential as quantum bits (qubits) for future quantum information technologies. One of their key features is a coherent optical interface, which allows quantum information to be transferred between 'static' electronic and nuclear spin states and 'flying' photons, and which facilitates their use in quantum communications systems and the construction of networks for scalable quantum processors. However a significant bottleneck in recent years has been the low efficiency (~1%) of this spin-photon interface, which places limitations on scalability and therefore the impact that this approach has achieved. Research efforts to address this challenge focus on exploring new colour centres and on integrating NV centres into optical microcavities.This project will investigate the use of a novel type of microcavity based on a monolithic Fabry Perot design, akin to those widely used in semiconductor devices such as vertical cavity surface emitting lasers which are grown by epitaxial techniques. Diamond does not support heteroepitaxial growth, so the cavity mirrors will be sputtered dielectrics (which are commercially available) deposited on either side of a thin diamond membrane. The student will develop techniques for forming the membranes to realise stable cavity modes with high quality factors, which are required to enhance the coherent spin-photon coupling strength. This will involve surface patterning to make microlens structures, using techniques such as focused ion beam milling and photolithography which are available in the host department. Key figures of merit will be the control over the shape of the surface as a means to determine mode geometry, and the surface roughness which determines the maximum mirror reflectivity as limited by scattering losses. These parameters will be measured using optical profilometry and atomic force microscope respectively. The student will characterise the resultant cavity devices using optical spectroscopy of the cavity modes, facilities for which exist within the host research group. The objective will be to achieve cavity modes with Purcell factors of 50 by the end of the project, which would be expected to translate to an interface efficiency of around 70%.The project falls within the EPSRC Quantum Technologies research area, and the research group is part of the UK Hub in Quantum Computing and Simulation. Through this programme, the project will involve collaboration with UK companies Element Six Ltd, who supply high specification synthetic diamond, and Oxford Instruments Plasma Technologies, who provide bespoke diamond etching capabilities. A spin-out company developing diamond quantum technologies is also planned which, if realised, will interface with the project and will be a potential route for commercialisation of the project outputs.