Controlling the Crystal Environment: Making a Thorium-229 doped Calcium Fluoride Nuclear Clock Seaworthy

At the start of the age of Discovery, Gemma Frisius laid out the concepts of triangulation and position determination using clocks on the vast seas. He was mocked for it, but nearly 500 years later clocks are the basis for measurements in fundamental physics, geodesic/environmental measurements and GPS. As clock were driven first by springs, then microwaves and finally visible light we continue this development by exciting the nucleus of thorium-229 with vacuum ultraviolet light to build a nuclear optical clock. Recently, by developing highly transparent calcium fluoride (CaF₂) crystals doped with thorium-229, several jumps in precision spectroscopy of the nucleus succeeded. Following this success, other crystal host materials were shown to work as well. This jump in advancement culminated in hyperfine spectroscopy of the nucleus, only observed in CaF₂ until now, where the effect of the environment on the nuclear two-level system can be measured. The CaF₂ environment can cause nonradiative decay (quenching) of the excited state. The environment also shifts, broadens and splits the nuclear excitation energy as observed in Mössbauer spectroscopy. We identify several thorium dopant site configurations, even thorium clusters, which are effectively modulated environments that have distinct effects on the nuclear state through electromagnetic interactions.As ship clocks only became precise enough by compensating for temperature drifts by for example bimetal strips, we intend to exploit the crystal environment to operate a solid-state nuclear clock more precisely. In this talk I will present the basic solid-state physics, give an overview of all the recent observations, explain the mechanisms and show how these can be used to improve a crystal nuclear clock. Finally, I will detail our future direction of research and applications of this clock in fundamental physics.