BSM-PM: Investigation of the Low-Lying Nuclear Isomeric Transition in Thorium-229

This award supports the development and exploration of the low-lying nuclear isomeric transition in the A = 229 isotope of thorium. This transition is expected to allow the construction of a nuclear optical clock with performance exceeding that of current atomic clocks. This enhanced performance will allow improvement of global positioning, communication, inertial navigation, and sensing systems. It will also provide the most sensitive test to date, by several orders of magnitude, of the variability of the fundamental constants of nature as well as new methods for searching for ultralight dark matter. The main research objective of this project is to develop techniques, including laser systems, crystals, and protocols, for using the nuclear transition for these goals as well as to understand the effects of the crystalline host on the nuclear transition. This project thus has the ability to aid the progress of science and in the near-term bolster national prosperity and security. Very recently, with NSF support, the PI demonstrated laser excitation and measurement of this nuclear transition at 8.355733(2)stat(10)sys eV in a 229Th-doped LiSrAlF6 crystals. The PI and his group observed a radiative lifetime for this transition of 568(13)stat(20)sys s in the crystal. This lifetime is sufficient for a high performance, solid-state based nuclear optical clock. Through this award, these researchers will further refine this measurement by use of a narrower laser system, study the effects on the nucleus due to the crystalline environment, and begin preparation for a measurement of the variability of the fundamental constants. Further, the group will work to explore alternative crystal hosts to the currently employed LiSrAlF6 crystal that may offer improved performance as well as novel, improved laser systems for creating the necessary 148 nm photons for control of this transition. Thus, the overarching goal of this project is to break open a new field in nuclear physics by providing means for full quantum control of a nucleus. Finally, this proposal will also allow the training of several high school and undergraduate students, graduate students, and a postdoctoral researcher in state-of-the-art techniques and modern science. Past students have gone on to careers in the quantum workforce, government labs, and the private sector. The PI anticipates the current students will have similar broad impacts on our country’s workforce. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.