Micro-fabricated cold-atom devices

社会和商业越来越依赖于全球导航卫星系统的精确定时，而全球导航卫星系统很容易出现故障和中断。皇家工程院估计，英国经济的7%左右依赖于GNSS，随着现代技术和商业运营对定时需求的不断增长，这一数字预计将上升。例如，美国国土安全部2017年报告指出，19个关键基础设施中有15个依赖GNSS定时。随着目前的精确计时系统变得过时，世界正在积极寻求新的模式来实现未来的创新，并非常重视全球机构通过开发紧凑的量子技术来解决这些问题[1，2]。拟议的博士项目旨在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IP，以促进领先的冷原子技术的可访问性的一步变化，用于精确定时应用，并最终用于其他测量场景。激光冷却的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的数量级更准确和精确，这是它们长的询问时间和未扰动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部化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，在循环原子共振以下调谐，以将原子的温度和速度降低到微开尔文状态，并使用附加技术降低到纳米开尔文状态。大型实验装置围绕超高真空（UHV）室建造，以提供适度的碱密度和无污染物的低背景压力。维持这些真空条件所需的主动泵送通常由离子泵提供。然而，离子泵运行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，包括微加工光学元件和主动泵浦芯片级真空单元[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UHV电池，并能够通过新颖的电池闭合技术将这些电池与较大的泵送装置分离。该项目将启动对被动泵浦技术的深入研究，如商业上可用的非蒸发吸气剂（NEGS），结合硅光子学和键合技术，以制造一种压力低于10^-7毫巴的电池，该电池可以在没有主动泵浦的情况下持续一年。原子能技术也将成为加速计、重力计和陀螺仪等一系列精密传感器的核心。原子（量子）系统能够将通过原子参数测量的外部扰动与频率测量联系起来，这意味着这些研究的最终成果将有助于开发下一代原子传感器。

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.