compact Cold-Atom Sources (cCAS)

We shall develop compact cold-atom sources for the alkali metals rubidium, caesium and potassium; and for the alkaline-earth metal strontium (Sr). These are very suitable for a range of applications in quantum technology and a components in the construction of apparatus for scientific research more broadly.

Magneto-optical traps (MOTs) can capture slow atoms directly from an atomic vapour at room temperature to provide a very convenient source of cold atoms. We have used an arrangement of four triangular mirrors arranged as a pyramid inside the vacuum region to make a MOT in three separate experiments over the years. Recently we developed an improved design that is more compact and adjustable than other sources. A patent application covering the innovative features of this pyramid-MOT was applied for in April 2016 and we are constructing a prototype working with rubidium (Rb). We will develop this into a commercial product integrated with a laser system produced by M Squared Lasers (MSL). The company's titanium-doped sapphire lasers provide a high power, relative to other tuneable lasers, and unmatched stability. We shall make full use of the available laser power by tailoring the size of the mirrors and enclosing vacuum chamber to produce a high flux of atoms. This will a give strong signals and high repetition rate of measurements in instruments such as atomic interferometers which as the basis of the quantum technology used in gravimeters, gyroscopes etc. This device can laser cool the other alkali metal atoms Cs and K, and light at all the wavelengths required is available from MSL. Compact and reliable cold-atom sources are of themselves a useful device that can be sold in the scientific equipment market that constitutes much of MSL's present sales.

While working on compact cold-atom sources we have noted the rapidly increasing interest in using cold strontium atoms for optical-lattice clocks, matter-wave interferometers and experiments with ultracold quantum gases. Strontium has intrinsic advantages such as rapid laser cooling, insensitivity to external magnetic fields and, for some isotopes, inter-atomic collisions are almost negligible. However working with cold Sr atoms much more technically demanding than Rb. In the traditional approach to laser cooling this species Sr atoms pass along the axis of a tapered solenoid (so-called Zeeman slowing developed in the 1980s) and many more laser wavelengths are required than for an alkali metals (Rb etc.) - up to 6 wavelengths for a Sr optical-lattice clock. However the availability of reliable lasers (from MSL) will make it possible to use Sr in products in the short term (within 5 years). Reportedly there have been attempts to make more compact sources of cold Sr using approaches similar to those for Rb but, for reasons explained in the proposal, a different method is more feasible. Our approach combines aspect of Zeeman slowing with long magnets with the compactness of in-vacuum mirrors (as in our pyramid design). In a further step we can develop this into a pulsed source that allows rapid loading of a high number of atoms (e.g. in 0.01 s) but with a much reduced flux of atoms during the measurement period (e.g. 1 s for some clocks). This mode of operation, with a pulsed valve, conserves atoms so that the oven does not need frequent reloading which is inconvenient especially for a field-deployed interferometer. The team in Oxford are not using Sr (although the PI has in the past) but the expertise is available to build the novel design (with features that we can patent, as in the work on Rb). The optimum outcome would provide a competitive edge for a product manufactured by MSLs. Licensing, or other, will be managed through Oxford University Innovation Ltd (as for the cold-atom source of Rb) to protect the technology and ensure that it remains part of a UK-based industry.

The core of this proposal an intense effort over 12 months to bring a cold-atom source to market in collaboration with the world-leading company M Squared Lasers. The majority of M Squared's revenues are associated with the SolsTiS solid-state laser that is class-leading in atomic and molecular physics applications. As such, M Squared has been selling into and enabling the global QT community for the last 10 years. These achievements have been recognised by the award of the Swan gold medal and prize (2016) of the Institute of Physics (UK) to Dr Graeme Malcolm OBE who is a co-founder and the current CEO. The IoP state that "Dr Graeme Malcolm is a leading expert in the commercialisation of photonics. Through his research, the design of innovative products, and the creation of high-growth companies, he has demonstrated a steadfast commitment to commercialise novel science." This project fits this successful strategy and enhances the competiveness of the UK by contributing to the large QT programme, in particular optical-lattice clocks and matter-wave interferometers. Many economic, social and environmental impacts accruing from QT are described in the material submitted to Innovate UK. High-flux cold-atom sources are also used to make cold atomic ions for improved Focussed Ion Beam (FIB) machining, by a start-up company in the US (zeroK Inc.), which is of major importance in semiconductor fabrication industry (for diagnosing problems rather than routine processing), and in associated industrial and academic research.

The feasibility study of a compact source of cold strontium atoms facilitates the construction and deployment of optical-lattice clocks. The aim is to make a device that can be supplied to customers outside the world's major metrology institutes where the science has been proven. After the project to integrate the vacuum and laser systems, any further work would be carried out with a wider consortium. This is likely to include the National Physical Laboratory, UK; so far only informal discussions have taken place but this is consonant with the NPL's remit and wide involvement in QT activities in the UK, and also the interests of the personnel. Professor Foot is the joint supervisor (with Professor Patrick Gill) of three graduate students working at NPL (one of which is on the Sr clock).