RUI: PM: Optical Molecular Clocks for New Physics Searches

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Some atoms and molecules possess quantum states with properties that are particularly well-suited to use in timekeeping, quantum information, or tests of physical laws. This award focuses on molecular vibrations – where the atomic nuclei stretch and compress the chemical bond. The project will demonstrate the tools needed to use molecular vibrations as precise frequency references (that is as good clocks) and is a stepping stone on the way towards searching for changes in the basic physical parameters of nature (such as how many times heavier the proton is than the electron). Such changes are predicted by some models of quantum gravity or dark matter, but none have yet been observed in the lab. This research takes place at a liberal arts college, and undergraduate students are involved in all aspects of the work. The project will advance the career of a postdoctoral scholar. In addition to training the next generation of scientists, this work develops skills in experimental physics that are transferable to a wide array of future endeavors.This award enables investigation of laser-driven vibrational transitions in molecular ions. The particular transition here – from the ground vibrational state to a vibrationally excited state in the diatomic oxygen molecular cation – has a narrow natural linewidth, high sensitivity to changing fundamental constants, and long-term prospects as an optical molecular clock. The nonpolar nature of the molecule suppresses systematic shifts related to electric fields, such as AC Stark shifts and blackbody radiation. Molecular vibrations hold great promise for next-generation searches for drifts or oscillations in the proton-to-electron mass ratio. This project builds on the PI’s experience with trapped charged particles as well as existing infrastructure for producing quantum-state-selected molecular ions. These ions will be loaded into a trap and sympathetically cooled with co-trapped atomic ions. The trapping enables long probe times, which will be needed to precisely determine the transition frequency and to demonstrate a proof-of-principle search for variation in the proton-to-electron mass ratio. Such a search is a probe of additional dimensions, new scalar fields, and ultralight dark matter.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.