Micro-fabricated cold-atom devices

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.