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（qubits）潜力。它们的关键特征之一是相干光接口，它允许量子信息在“静态”电子和核自旋态与“飞行”光子之间传输，这有助于它们在量子通信系统和可扩展量子处理器网络的构建中使用。然而，近年来的一个重要瓶颈是这种自旋光子界面的低效率（~1%），这限制了可扩展性，因此影响了这种方法所取得的成就。解决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。该项目将研究一种基于单片法布里·佩罗设计的新型微腔的使用，类似于那些广泛用于半导体器件的微腔，如通过外延技术生长的垂直腔面发射激光器。金刚石不支持异质外延生长，因此腔镜将被溅射电介质（这是商业上可用的）沉积在薄金刚石膜的两侧。该学生将发展形成膜的技术，以实现具有高质量因子的稳定腔模式，这需要增强相干自旋光子耦合强度。这将涉及到表面图案，以制造微透镜结构，使用技术，如聚焦离子束铣削和光刻，可在主机部门。关键的优点是对表面形状的控制，这是确定模态几何形状的一种手段，而表面粗糙度决定了受散射损失限制的最大镜面反射率。这些参数将分别用光学轮廓术和原子力显微镜进行测量。学生将使用空腔模式的光谱学来表征所得到的空腔设备，这些设备存在于宿主研究小组中。目标是在项目结束时实现珀塞尔系数为50的空腔模式，预计将转化为70%左右的界面效率。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。通过该项目，该项目将与提供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，该公司将与该项目对接，并将成为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.