Cold-atom source of strontium for Quantum Technology
Lead Research Organisation:
UNIVERSITY OF OXFORD
Department Name: Oxford Physics (Keble Road)
Abstract
Accurate navigation on earth and in space relies on precise and accurate timekeeping. Better clocks will give faster data transfer, improved positioning, and new science applications. A significant and increasing fraction of the UK GDP depends on Global Navigation Satellite Systems (GNSS) technologies. Location based services associated with mobile broadband services are driving further growth. Thus ensuring the proper dissemination of time from the worldwide network of National Metrology Institutes (NMIs) is essential to the functioning of the economy and infrastructure of the UK, and other developed countries. Networked systems have vulnerabilities, however, and these risks need to be mitigated by having standalone oscillators distributed in the system that can continue providing the required service. The new generation of optical clocks provides a 100 times better performance and will enhance the capabilities of GNSS. As systems evolve to make use of this higher precision it is vital to improve the `holdover' technology in order to guarantee continuity. Atomic microwave clocks have been available commercially for many years and are at the heart of communication systems, e.g. a contributor to the synchronization of GPS is the ensemble of over 50 devices maintained at the US Naval Observatory.
Clocks use the internal energy levels of atoms to control the frequency of an oscillator accurately. Optical clocks that use lasers to interrogate atomic transitions are several orders of magnitude better than devices based on microwave transitions because the optical transitions have higher frequency and are chosen to have a higher 'quality factor'. Laser cooling of atoms has revolutionised timekeeping and this dramatic change is spreading to other quantum technologies for precision measurements such as matter-wave interferometers used as inertial sensors for navigation and gravimeters for surveying. There are also major research applications of atom interferometry in fundamental physics such as new types of detector for dark matter and gravitational waves. The experimental methods that are being developed to build atom interferometers with large baselines (kilometre scale) use the special properties of the extremely narrow clock transition in strontium atoms and adapt the technology that has been developed for optical clocks. This project seeks to develop a source of laser-cooled strontium atoms that is a key component in the supply chain for the fabrication of the next generation of such quantum devices.
This project will support the development of a high-flux cold-atom source of strontium to a Technology Readiness Level at which it can be supplied to others for integration into instruments. We will also test new aspects of atom sources such as pulsed operation to prolong the lifetime, which is an important consideration for the deployment of clocks and quantum instruments outside of research laboratories, for example in projects to build very large-scale interferometers in deep shafts where access is restricted.
Clocks use the internal energy levels of atoms to control the frequency of an oscillator accurately. Optical clocks that use lasers to interrogate atomic transitions are several orders of magnitude better than devices based on microwave transitions because the optical transitions have higher frequency and are chosen to have a higher 'quality factor'. Laser cooling of atoms has revolutionised timekeeping and this dramatic change is spreading to other quantum technologies for precision measurements such as matter-wave interferometers used as inertial sensors for navigation and gravimeters for surveying. There are also major research applications of atom interferometry in fundamental physics such as new types of detector for dark matter and gravitational waves. The experimental methods that are being developed to build atom interferometers with large baselines (kilometre scale) use the special properties of the extremely narrow clock transition in strontium atoms and adapt the technology that has been developed for optical clocks. This project seeks to develop a source of laser-cooled strontium atoms that is a key component in the supply chain for the fabrication of the next generation of such quantum devices.
This project will support the development of a high-flux cold-atom source of strontium to a Technology Readiness Level at which it can be supplied to others for integration into instruments. We will also test new aspects of atom sources such as pulsed operation to prolong the lifetime, which is an important consideration for the deployment of clocks and quantum instruments outside of research laboratories, for example in projects to build very large-scale interferometers in deep shafts where access is restricted.
People |
ORCID iD |
| Christopher Foot (Principal Investigator) |
| Description | We designed a new type of oven from atomic strontium which is simple to construct and operate. We have manufactured and tested a nozzle from glass which has tens of thousands of channels for collimating the atoms into a high-flux beam. This can be mass produced and can be scaled up much more easily than the traditional method of stacking capillary tubes by hand, or mechanical drilling. This design has been proven to work well in experimental tests over many months. A detailed study of the physics underlying the operation of the source has been carried out written up for publication. A high-flux source of strontium atoms is required for cold atom quantum technology applications. Our re-entrant oven design avoids the need for any vacuum feed-throughs and has an inherent temperature gradient to guard against clogging of the nozzle. The nozzle is fabricated by micro-machining of fused silica using selective laser etching; this specialised technique is capable of making many thousands of fine microchannels and is suitable for batch production. We also developed a heated in-vacuum sapphire window, giving optical access directly opposite the oven, which can be cleared of metallization without breaking vacuum. We used this optical access to modulate the flux of the atomic beam by direct illumination of the nozzle and the strontium metal with high-power laser light. Heating by laser light increased the useful flux by a factor of up to 16 on a timescale of 40 s, and a factor of 2.5 on a timescale of 1 s. This rapid flux modulation serves to increase the operating lifetime of the oven. We report experimental measurements of the performance in long-term operation over several months. For alkaline earth atoms such as strontium, high temperatures are required to achieve a vapour pressure to produce an atomic beam for cold atom experiments. Various types of atomic oven have been demonstrated, optimized for a range of applications such as a high flux, a highly collimated atomic beam, or a compact source. Atomic ovens are typically designed to operate as effusive sources and commonly use a multichannel capillary array to collimate the output atomic beam, increasing the fraction of atoms that can be used in subsequent experiments. Stacking capillary tubes is straightforward, but cannot be easily scaled for large channel numbers or batch production of sources. Our compact, re-entrant oven design with a laser-etched glass nozzle and a heated sapphire window through which we modulate the atom flux with high-power laser light. This approach achieves a high flux, efficient usage of strontium. Nozzles with over 100 000 holes have been fabricated by this method but not yet tested; the proof-of-principle measurements reported here indicate the utility of this approach and that there is a large scope for developing it further. This represents a considerable advance on previous work on developing atom sources that use laser light to produce the atomic vapour ranges from light-induced atomic desorption to laser-induced thermal ablation. In almost all cases, the light is focussed down to sub-millimetre beam waists, and in used to produce a vapour in a glass cell rather than for applications that require an atomic beam. The use of light to produce a collimated beam of Sr via optical heating has been demonstrated for systems requiring low fluxes (~10^7 atoms/s). Our system with combined electrical and optical heating produces a high flux of Sr atoms (up to >10^14 atoms/s) in a collimated beam. Modulation of the flux from the oven by using a pulse of high-power laser light to briefly increase the flux allows the system to be run at a lower base temperature, while also reducing the amount of Sr deposited on the chamber walls; the build-up of dendritic whiskers can interfere with optical beam paths. This extends the lifetime of the oven, defined as the time taken for the supply of Sr in the oven to be fully depleted. |
| Exploitation Route | High-flux sources of strontium are needed for several applications, as described in the original proposal, and the PI has links with a project to make a large-scale atom interferometer which would benefit from a higher cold-atom flux. Work to develop this approach further is ongoing and we are exploring whether there is commercial interest. Our results demonstrate a robust method for collimation and modulation of an atomic beam of strontium suitable for long-term operation. However, these are far from the limits of this approach and even higher atomic fluxes could be obtained with further development. |
| Sectors | Aerospace Defence and Marine |
| Description | This high-flux cold-atom source will enhance quantum timing and navigation. |
| First Year Of Impact | 2025 |
| Sector | Aerospace, Defence and Marine |
| Description | Dr Joe Goodwin |
| Organisation | University of Oxford |
| Department | Department of Physics |
| Country | United Kingdom |
| Sector | Academic/University |
| PI Contribution | We have tested a new type of nozzle made from glass and shown that it does not degrade in a high flux of strontium (hot strontium vapour). |
| Collaborator Contribution | Dr Goodwin has set up a spin-out company producing very compact low-flux strontium atoms oven based in Oxford Physics. We are using a similar technology based on laser drilling and etching of glass to produce a novel type of nozzle for our system. We have exchanged information about manufacturers but have chosen to use different companies. |
| Impact | Before the end of the grant period we plan to demonstrate a high-flux source of strontium which could be commercialised, either independently or through the spin-out entity that already exists. |
| Start Year | 2024 |
| Description | Participation in Open Evening of lab tours for the general public |
| Form Of Engagement Activity | Participation in an open day or visit at my research institution |
| Part Of Official Scheme? | No |
| Geographic Reach | Local |
| Primary Audience | Public/other audiences |
| Results and Impact | The attendees were a mixture of schoolchildren and adults. |
| Year(s) Of Engagement Activity | 2023,2024 |
| URL | https://www.physics.ox.ac.uk/engage/public-and-community/open-door-events |