Micro-fabricated cold-atom devices

社会和商业越来越依赖全球导航卫星系统（GNSS）的精确授时，而这些系统很容易发生故障和中断。英国皇家工程院估计，大约7%的英国经济依赖于GNSS，随着现代技术和商业运营对定时需求的不断增长，这一数字预计还会上升。例如，2017年美国国土安全报告指出，19个关键基础设施中有15个依赖GNSS授时。随着当前精密定时系统的过时，世界正在积极寻求新的模式来实现未来的创新，将重点放在全球机构上，通过紧凑量子技术的发展来解决这些问题[1,2]。拟议的博士项目寻求与当地的光子学和量子技术供应链制造商合作，开发技术和知识产权，以促进在精密定时应用和最终其他测量场景中领先的冷原子技术的可及性的逐步变化。激光冷却原子是现代精密测量的核心，因为它们的慢速度意味着它们在计量测量中要精确几个数量级，这是它们长时间的探测和不受干扰的原子结构的直接结果。冷原子实验的主力是磁光阱（MOT）[4]。该系统利用平衡的光辐射力来减少由梯度磁场提供的空间局域陷阱中的热原子的动量。MOT的典型形成使用6个反向传播的激光场，调谐到循环原子共振以下，将原子的温度和速度降低到微，并使用额外的技术，纳米开尔文状态。大型实验装置是围绕超高真空（UHV）室建造的，以提供适度的碱密度和低背景压力，无污染物。维持这些真空条件所需的主动泵通常由离子泵提供。然而，离子泵工作所需的高电压消耗和大磁场不利于紧凑的原子装置和精密仪器。最近的研究着眼于激光冷却设备的小型化和便携性，包括微制造光学元件和主动泵浦芯片级真空电池[5]。尽管最近的研究在实现紧凑的冷却装置方面取得了重大进展，但实现真正芯片级冷原子平台的能力仍然难以捉摸。目前的项目旨在开发能够被动泵送的芯片级特高压电池，并能够通过新颖的电池封闭技术将这些电池与更大的泵送设备分离。该项目将启动对被动泵送技术的深入研究，如商业上可用的非蒸发吸收器（NEGS）与硅光子学和键合技术相结合，以制造压力低于10^-7毫巴的电池，该电池可以在没有主动泵送的情况下在该水平下持续一年。除了为地面和天基计时技术提供下一个里程碑之外，小型化冷原子技术还将成为一系列精密传感器（如加速度计、重力仪和陀螺仪）的核心。原子（量子）系统将通过原子参数测量的外部扰动与频率测量联系起来的能力意味着，最终，这些研究的高潮将有助于下一代一系列原子传感器的发展。

Society and commerce are increasingly reliant on precision timing from global navigation satellite systems (GNSS), which are vulnerable to failure and disruption. The Royal Academy of Engineering estimates that around 7% of the UK economy is dependent on GNSS, with this number expected to rise with growing need for timing in modern technology and business operations. For example, the US homeland security report 2017 state that 15 out of 19 critical infrastructures rely on GNSS timing. With current precision timing systems becoming obsolete, the world is actively pursuing new modalities to enable future innovation, placing a large emphasis on global institutions to tackle these issues through the development of compact quantum technologies [1, 2]. The proposed PhD project seeks to work with a local photonics and quantum technology supply chain manufacturer to develop technology and IP to facilitate a step change in accessibility to the leading cold-atom based technologies for precision timing applications and ultimately other measurement scenarios. Laser cooled atoms are central to modern precision measurements, as their slow speed means they are orders of magnitude more accurate and precise for metrological measurements as a direct result of their long interrogation times and unperturbed atomic structure. The workhorse of cold-atom experiments is the magneto-optical trap (MOT) [4]. This system utilises a balanced optical radiation force to reduce the momentum of thermal atoms in a spatially localised trap provided by a gradient magnetic field. The typical formation of the MOT uses 6 counter-propagating laser fields, tuned below a cycling atomic resonance to reduce the temperature and velocity of atoms to micro-, and with additional techniques, nano-Kelvin regimes. The large-scale experimental apparatus is built around an ultra-high vacuum (UHV) chamber to provide a modest alkali density and low background pressure free of contaminants. The active pumping required to maintain these vacuum conditions is typically provided from an ion pump. However, the high voltage consumption and large magnetic field that are required for the ion pump functioning, are unfavourable for compact atomic devices and precision instruments. Recent studies have looked at the miniaturisation and portability of laser cooling apparatus, including microfabricated optical elements and actively pumped chip-scale vacuum cells [5]. Although recent studies have made significant progress to achieving a compact cooling apparatus, the ability to achieve a truly chip-scale cold atom platform remains elusive. The current project aims to develop chip-scale UHV cells capable of passive pumping and the ability to separate such cells from the larger pumping apparatus through novel cell closure techniques. The project will initiate thorough studies of passively pumped technologies such as commercially available non-evaporable getters (NEGS) in conjunction with silicon photonics and bonding techniques to fabricate a cell with pressures below 10^-7 mbar that can be sustained at this level for a year without active pumping.In addition to providing the next milestone in terrestrial and space-based timing technology miniaturised cold-atom technology will also be at the core of a range of precision sensors such as accelerometers, gravimeters and gyros. The ability for an atomic (quantum) system to link an external perturbation to be measured through atomic parameters to a frequency measurement means that ultimately, the culmination of these studies will aid the development of next generation of a range of atomic sensors.