Micro cavities for efficient atom-photon coupling by quantum-electrodynamic effects (project supervised by A. Kuhn, Oxford, including secondments

高精密光学腔，使用强弯曲镜将光限制在一个小体积内，使得从单个原子、离子或其他量子发射器中有效地提取单个光子成为可能。目前最先进的曲率半径（ROC）为5cm ROC的空腔已经达到强耦合状态的开始，其中腔内的相互作用可与不受控制的自发发射率相媲美。这样的腔实现了50%的光子提取效率，并允许控制光子的偏振和时间分布。本项目旨在探索、设计和构建具有1mm ROC的新型微腔。更严格的约束将导致耦合强度前所未有的10倍提高，这将允许在强耦合范围内深入探索量子电动力学现象，以及允许更有效的光子提取。除了表征、测试和组装新空腔外，该项目同样旨在现场演示它们与被困在空腔场模式体积中的单个原子有关的能力。该项目将空腔量子电动力学领域推向了超强耦合状态，并且需要学生在几个研究小组之间协调空腔的生产。将有机会前往苏塞克斯郡使用镜面加工设备，并前往美国和德国的镜面涂层公司。库恩博士的研究团队确实包括两名博士后和四名研究生，他们在牛津大学物理系管理着2-4个实验室，专门研究腔内量子耦合和腔内原子光子耦合。工作空间设备齐全，包括3-4个用于研究腔内原子-光子耦合的真空室，几个ECDL和光纤激光器用于原子操作，一个同步稳定所有激光和腔频率的频率梳，一个大的单光子计数器和一个腔表征装置，以及一个AFM用于近距离检查镜面。此外，苏塞克斯郡的二氧化碳激光加工设备和牛津材料公司的离子束铣削设备将是该项目不可或缺的一部分。该项目将影响NQIT中心，该中心是EPSRC量子技术研究领域内的UKNQTP量子技术中心之一。它将为NQIT的里程碑做出贡献，最重要的是实现高曲面镜面，与NQIT合作伙伴Smith和Keller合作，使用聚焦离子束铣削和激光加工。此外，高精细镜面涂层的规格和生产需要与镜面涂层公司密切合作，如Garbsen的LaserOptik或Boulder的ATF。该项目将加速实现M2.3高精细光纤腔、M2.4原子腔耦合、M2.5强腔耦合、M2.7腔介导的远程纠缠等里程碑。所有必要的设备都存在于NQIT中，包括离子束铣削（牛津材料公司），二氧化碳激光加工系统（苏塞克斯公司），用于表征镜面的波前传感器和原子力显微镜（牛津物理公司），以及驱动光子生产过程的所有必要激光器（牛津物理公司）。

High-finesse optical cavities, which use strongly curved mirrors to confine light to a small volume, have made it possible to efficiently extract a single photon from a single atom, ion, or other quantum emitter. Current state-of-the-art cavities with radii of curvature (ROC) of 5cm ROC have reached the beginning of the strong-coupling regime, where the interaction in the cavity is comparable to rate of uncontrolled spontaneous emission. Such cavities achieve ~50% photon extraction efficiency and allow for controlling the polarisation and temporal profile of the photon. The aim of this project is to explore, design and construct new microscopic cavities with a 1mm ROC. The tighter confinement would lead to an unprecedented 10x improvement in coupling strength, which would allow the exploration of Quantum Electro-dynamical phenomena deep within the strong-coupling regime, as well as allowing more efficient photon extraction. Beside the characterisation, testing and assembly of novel cavities, the project is equally aiming at the in-situ demonstration of their capabilities in connection with single atoms trapped in the mode volume of the cavity field.The project pushes the field of cavity quantum electrodynamics into the ultra-strong coupling regime, and will need the student to co-ordinate the production of cavities between several research groups. There would be opportunities to travel to Sussex to use the mirror machining apparatus and to mirror-coating companies in the US and in Germany. The research team of Dr Kuhn does encompass two PostDocs and four graduate students which operate 2-4 laboratories dedicated to cavity-qed and atom-photon coupling in cavities at Physics department of the University of Oxford. The work space is well equipped, comprising 3-4 vacuum chambers for studying atom-photon coupling in cavities, several ECDL and fibre lasers for atom manipulation, a frequency comb for synchronously stabilising all laser and cavity frequencies, a large battery of single-photon counters and a cavity-characterisation setup and an AFM for the close inspection of mirror surfaces. Furthermore access to the CO2-laser machining facility in Sussex and the Ion-Beam-Milling apparatus at Oxford materials will be integral part of this project.This project will impact upon the NQIT Hub, one of the UKNQTP's Quantum Technologies Hubs within EPSRC's Quantum Technologies research area. It will contribute to NQIT's milestones, most significantly to achieve a highly-curved mirror surface, using focussed ion beam milling and laser machining in collaboration with NQIT partners Smith and Keller. Furthermore, the specification and production of high-finesse mirror coatings would require a close collaboration with mirror-coating companies such as LaserOptik in Garbsen or ATF in Boulder. The project would accelerate achievement of the milestones M2.3 High-finesse fibre cavity, M2.4 Atom-cavity coupling, M2.5 Strong cavity coupling, M2.7 Cavity-mediated remote entanglement. All necessary apparatus exists within NQIT, including ion-beam milling (Oxford Materials), CO2 laser machining system (Sussex), wavefront sensor and AFM for characterising the mirror surfaces (Oxford Physics), and all necessary lasers for driving the photon production process (Oxford Physics).