ThF thin films for solid-state nuclear clocks.

After nearly 50 years of searching, the vacuum ultraviolet Th nuclear isomeric transition has recently been directly laser excited and measured with high spectroscopic precision. Nuclear clocks based on this transition are expected to be more robust than and may outperform current optical atomic clocks. These clocks also promise sensitive tests for new physics beyond the standard model. In light of these important advances and applications, a substantial increase in the need for Th spectroscopy targets in several platforms is anticipated. However, the growth and handling of high-concentration Th-doped crystals used in previous measurements are challenging because of the scarcity and radioactivity of the Th material. Here we demonstrate a potentially scalable solution to these problems by performing laser excitation of the nuclear transition in ThF thin films grown using a physical vapour deposition process, consuming only micrograms of Th material. The ThF thin films are intrinsically compatible with photonics platforms and nanofabrication tools for integration with laser sources and detectors, paving the way for an integrated and field-deployable solid-state nuclear clock with radioactivity up to three orders of magnitude smaller than typical Th-doped crystals. The high nuclear emitter density in ThF also potentially enables quantum optics studies in a new regime. Finally, we present the estimation of the performance of a nuclear clock based on a defect-free ThF crystal.