Trapped ion clock with enhanced reliability (TICKER)

The 'trapped ion clock with enhanced reliability' project (TICKER) brings together world leading expertise in metrological-grade ion trap development, ultrastable room-temperature cavity-stabilised lasers, and laser source development to deliver unprecedented performance in a field-deployed state-of-the-art optical clock.
Optical atomic clocks (OACs) have made extraordinary improvements over the last few decades and represent the pinnacle of precision measurement technology. The extreme accuracy of OACs enables exciting new opportunities for both fundamental physics and technology from detecting dark matter, relativistic geodesy, and improving satellite navigation accuracy. However, the science and technology impact from the current generation optical atomic clocks has been limited for the wider technology and industry base as they are fragile and complex laboratory-sized systems operated in well-controlled environments by skilled scientists. These limitations mean that only a handful of operational examples exist worldwide, restricted to National Metrology Institutes (NMIs) such as NPL. To unlock the transformative potential from OACs they must become simpler and more robust. This cannot be achieved by simply shrinking a laboratory clock; new approaches and technologies are called for.

We will develop the technologies that bypass these constraints and allow the creation of practical optical clocks, focusing on the singly ionised strontium-88 (Sr+) system as the most viable candidate. Within this project we will develop metrological-grade ion traps that are manufacturable and robust enough to operate in less-well-controlled remote locations and mobile platforms, a transportable environmentally insensitive optical reference cavity, and a 422-nm DFB laser as a low-power and robust source for laser-cooling the ion.
Atomic clocks based on trapped ions are inherently simpler and require lower power to operate than the other major class of high-performance clocks - neutral atom lattice clocks. Ion clocks also have relaxed requirements of the clock-laser, making them more suitable for noisy environments. Trapping and laser cooling a single ion requires less than a watt of RF power and less than a milliwatt of optical power; the electrode structure and vacuum system can be miniaturised and ruggedised using established techniques aided by finite element analysis. The Sr+ system is particularly attractive because the clock transition can be measured in a way that provides low sensitivity of the centre frequency to the environment. Additionally, the transitions in its simple energy level structure can mostly be addressed with commodity lasers. One exception is the 422-nm laser-cooling transition. Currently this light must be produced from either a vibration sensitive ECDL laser or inefficient frequency doubling from an infrared DFB laser. A 422-nm DFB laser would enable a great improvement in the SWAP and robustness.
NPL's patented cubic cavity design is the leading transportable and force insensitive design and will be adapted to suit the requirements of field-deployable atomic clocks. Reducing the volume of the cubic cavity spacer from 125 cc to 27 cc still provides good frequency stability while greatly reducing the required environmental shielding. Moreover, we have invented a novel technique that exploits material anisotropy to further reduce environmental impact, which will extend the temperature-insensitivity alongside the force- and vibration-insensitive design.
Together, with the addition of an optical frequency comb (being developed at pace under many other programs, to the requirements of optical clocks) we address the major challenges that are preventing optical clocks from field deployed applications.