Description
We have undertaken a series of measurements of atomic properties of group III and IV systems to test ongoing ab initio atomic structure calculations. These multi-valence systems have relevance to tests of symmetry violation and other fundamental physics searches. Prior work involved measurements of polarizability, isotope shifts, and hyperfine structure in various excited states of the three-valence thallium and indium systems.
Recently, we have focused on the four-valence Pb system where significantly improved atomic structure calculations [1] have been completed for an atomic system in which two different precise atomic parity nonconservation experiments were performed two decades ago. Unlike alkali systems, relatively few atomic benchmark measurements exist in Pb at a level of accuracy necessary to test and guide refinement of the theory. In 2019, we completed the first measurement of the forbidden Pb (6s$^{2}$6p$^{2}$) $^3$P$_0$ - $^3$P$_{2}$ E2 transition amplitude at 939 nm, finding excellent agreement with the ab initio value computed by the Safronova group at the 1% level of accuracy. The experimental method employed the same high-precision polarimetry technique used to measure parity non-conserving optical rotation. This technique, which uses crossed polarizers and a Faraday modulation / lock-in detection technique, yields $\mu$Radian precision, allowing measurement of very weak atomic transitions via detection of milliradian-sized Faraday rotation using small DC magneticfields applied to the sample.
We are currently pursuing several new Pb atomic structure measurements using this same Faraday polarimetry method. These include measurements of transition isotope shifts and hyperfine splittings in these forbidden transitions using isotopically-enriched vapor cells, as well as measurements of electric dipole amplitudes for transitions originating in thermally-excited levels with populations of order 10$^{-5}$ of the ground-state population.
Additionally we plan to measure, for the first time, excited-state polarizabilities in Pb, using the same atomic beam apparatus and high-voltage field-plate system used in our lab for prior measurements in indium and thallium. Here, a molybdenum crucible containing 300 g of lead is heated to above 1000 $^\circ$C to create a dense, collimated atomic beam. The sensitive Faraday polarimetry method will be used to perform transverse spectroscopy in the presence of this beam and static electric fields up to 20 kV/cm will create Stark shifts in the 368 nm (6s$^{2}$6p$^{2}$) $^3$P$_1$ - $(6s^{2}6p7s)^3P_{0}$ E1 transition. The predicted Stark shift is roughly half the expected Doppler-narrowed line width, and we expect to see Faraday rotation signals of order 100 $\mu$Radians, which should be easily measurable using our polarimetry technique, providing a new, exacting test of the atomic theory predictions.
Current results will be presented.
[1] D.L. Maser, Eli Hoenig, B.-Y. Wang, P.M. Rupasinghe, S.G. Porsev, M.S. Safronova, and P.K. Majumder, Phys. Rev A 100, 052506 (2019).
| Presenter name | Protik Majumder |
|---|---|
| How will you attend ICAP-27? | I am planning on in-person attendance |
