ABSTRACT

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).

General audience abstract:
We know that in the beginning of the Universe there were interactions, necessary for our existence, that violated time symmetry. But, we have yet to discover what these processes were. A few heavy radioactive elements hold promise to uncover the nature of these interactions because of enhanced sensitivity to time symmetry violating physics. Radium is one such element, and when incorporated into a molecule the sensitivity to time symmetry violation is further amplified. An experiment would measure the energy of molecular states in two different configurations: when the radium nucleus is aligned with the molecule?s electric field, and when the nucleus is anti-aligned with the electric field. The energy difference between the two configurations constrains time symmetry violating interactions. Because of their radioactivity radium and radium-based molecules have so far been little-studied. The PI and his students will build on recent advances with the radium ion to provide a complete picture of the ion's important low-energy electronic levels. Further, the team will study the rotational structure of radium-based molecules, and work towards controlling these radioactive molecules with the finest precision possible. Additionally, the PI and his students will lead sessions to improve Wikipedia science articles (freely accessible), with a focus on the field of atomic physics. These efforts will provide valuable training and learning opportunities for graduate students, undergraduate students, and high school students.

Technical audience abstract:
In this project the PI and his students aim to measure basic properties of the radium ion, and study and control the rotational structure of the molecular ion RaH+. They will measure the radium ion's 7P_1/2, 6D_3/2, and 6D_5/2 state lifetimes. The 7P_1/2 and 6D_3/2 lifetimes have yet to be measured, and there only exists a lower bound on the 6D_5/2 state. These measurements will provide a complete picture of the important low-lying excited states of Ra+, which is important for advanced work with this ion. In addition to studying the radium ion, the team will use Ra+ to produce and cool trapped RaH+ molecular ions. With an optical frequency comb the team will drive stimulated Raman transitions between rotational states of the molecule to study the rotational structure. They will be able to build upon the rotational measurements by controllably driving transitions between rotational states to populate a target rotational state of RaH+. The advances in rotational spectroscopy and control will open the door to high precision spectroscopy of heavy radioactive molecules which are appealing for constraining time symmetry violation that is important for understanding baryogenesis and the strong CP problem.

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.

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