基于单晶金刚石光波导的量子集成光子器件研究

Recently, diamond nitrogen-vacancy (NV) centre has been the focus of scalable quantum information processing (QIP) due to its exceptional properties. Diamond NV centre is room temperature single photon source. Optical control together with microwave manipulation of individual electron spins in diamond has also been demonstrated. Furthermore, electron spin of a single NV can be coupled the nearby nuclear spin. Therefore, Diamond NV center is the ideal platform to generate, manipulate and store quantum information. This makes diamond one of the candidates for solid state QIP. The interaction between diamond NV centres can be realized through photons guided along integrated diamond optical waveguide circuits. Diamond is chemically inert and it is still a huge challenge to fabricate photonic structures in single crystal diamond. Although photonic structures like straight waveguide and micro-ring have been demonstrated in single crystal diamond, functional components like directional couplers that are fundamental in integrated quantum circuits are still unavailable. Therefore, it is still not possible to perform quantum optics measurement based on single crystal diamond photonic circuits. In this project, we plan to design and fabricate waveguide based integrated quantum photonic components (i.e. directional coupler) in single crystalline diamond and demonstrate the two-photon interference (Hong-Ou-Mandel) experiment. This would provide very useful information towards the feasibility of using diamond for integrated quantum photonics. To the best of our knowledge, there is no report on diamond directional coupler yet which makes this project both exciting and challenging.

近年来，金刚石氮空位(NV)中心在量子信息学的应用备受关注。金刚石NV中心可以作为室温单光子源，其电子自旋可以被激光初始化和读取、在微波激励下翻转、还可和邻近原子的核自旋耦合，实现量子信息的产生、操纵和存储。因此，金刚石成为固态量子信息学研究的理想材料体系之一。金刚石NV中心自旋之间的长程相互作用可以经由光子为媒介来实现，在金刚石衬底上制备的集成光波导器件可以用来引导光子。由于金刚石的化学惰性，在单晶金刚石中制备光波导器件极具挑战性。尽管金刚石条形光波导和微环谐振腔等光子结构的制备已经取得了一定进展，但量子集成光路的功能元器件(例如方向耦合器)研究还很少，还不能在金刚石集成光路中进行量子光学实验。本项目计划在单晶金刚石上设计并制作基于光波导的集成光子器件（方向耦合器），演示双光子干涉等量子光学实验以验证金刚石量子集成光子器件的功能性。金刚石方向耦合器尚未见报道，这是本项目最大的创新点。

金刚石在与单光子源和自旋电子学相关的量子信息技术以及诸如拉曼激光器的经典应用中都非常有前景的材料。这些应用都可能需要基于金刚石波导结构来限制和实现光子路由，而量子信息应用格外依赖高的单光子收集效率，微透镜是增大单光子收集效率的有效方法。因此，单晶金刚石波导和微透镜是本项目的两大主要研究内容。.我们使用准各向同性等离子体蚀刻技术完成单晶金刚石波导和定向耦合器的制备。项目中将硅硬掩模转移到金刚石的表面以减少小样品光刻胶涂覆的制造困难。聚焦离子束方法用来刻蚀金刚石波导的两端上的输入/输出镜片。项目使用中心为632 nm的He-Ne激光器来测试波导，可以看到沿着波导有清晰的输入/输出光斑和散射光，这是本项目研究过程中取得的重要结果之一，关键数据在正文的图1.11，1.12和1.15中展示。这是可扩展的金刚石集成光子学的重要步骤。.单晶硅微透镜和具有0.6, 2.47和3.2微米的各种直径的二氧化硅微球分散在金刚石表面上作为微透镜的刻蚀硬掩模。使用等离子体刻蚀将这些三维的形状转移到金刚石薄片上。近半球形透镜轮廓通过调整刻蚀参数（包括气体混合比，压力和等离子体功率）来实现。我们使用了SEM和表面轮廓仪来验证微透镜的近半球形轮廓。这是本项目研究过程中取得的重要结果之一，关键数据在正文的图2.3, 2.11和2.12中展示。该方法对于制造直径和高度可调的金刚石微透镜阵列非常有用。.我们在国际上首次利用三维硬掩膜实现等离子体刻蚀近似半球的单晶金刚石微透镜阵列。使用准各项同性刻蚀方法制备了单晶金刚石光波导，达到了国际领先水平，属于国内首创。