Optical clocks are amazingly stable frequency standards, which would be off by only one second over the age of the universe. This precision is orders of magnitude better than the one of commercial frequency standards, which operate at microwave frequencies, and is enabled by the interrogation of ultranarrow optical transitions in atoms that are cooled to near standstill. So far these clocks have been complex, fragile and maintenance intensive devices, built by researchers and only usable with their experience. Bringing those clocks from the laboratory into a robust, compact and easy to use form will have a large impact on telecommunication and navigation (e.g. network synchronization, increased traffic bandwidth, GPS spoofing and outage resilience, terrestrial navigation with cm precision), geology (e.g. underground exploration, monitoring of water tables, volcanoes or ice sheets), astronomy and space (e.g. low-frequency gravitational wave detection, radio telescope synchronization, deep space navigation) and other fields.
To make this a reality, we have founded the iqClock consortium, assembling leading experts from academia, strong industry partners, and relevant end users. We will seize on recent developments in clock concepts and technology to start-up a clock development pipeline. The objectives of iqClock are arranged in four scientific work packages (WPs) along the technology readiness level (TRL) scale and one outreach WP. WP3 is building an industrial prototype of a field-ready, compact and robust optical lattice clock. The University of Birmingham’s (UoB’s) Quantum Sensing Hub has guided our industry partners (Toptica (laser systems), Teledyne e2v (vacuum chamber and control electronics), NKT Photonics (multicolour optical fibres), Acktar (internal black coating of vacuum chamber for stray light suppression)) in the development and production of the components of this clock. The components have been tested at UoB and integrated into a clock, which will soon be benchmarked in a real use case, the synchronization of a network simulator built by British Telecom (BT) and integrating test equipment developed by Chronos.
Three smaller scientific WPs have laid the foundation to develop a new type of optical clock, which promises enhanced robustness, reduced complexity and potentially better performance than existing types. Existing optical clocks reference their frequency to atomic transitions by shining laser light onto atoms and detecting how strongly the atoms get excited. This scheme leads to complications that could be circumvented if the atoms would not be passively interrogated, but be enticed to actively emit light on the optical clock transition, forming a laser beam. Our goal is to build the first continuously operating laser of this type, a “superradiant” laser. In WP4 we have built the simplest version of such a device, operating on a kHz-linewidth transition. We have demonstrated pulsed, quasi-continuous emission and have reached the regime in which continuous superradiance should be possible. In WP5 and 6 we have developed two complementary experimental apparatuses that can push the technology to the ultimate level, continuous superradiant lasing on mHz-linewidth transitions. In WP6 we theoretically and experimentally explored the foundations of superradiant lasing. These WPs have been executed jointly by partners from the Universities in Copenhagen (UCPH), Torun (UMK), Amsterdam (UvA), Vienna (TUW) and Innsbruck (UIBK).
