There is a long, fruitful history of precision measurements in low energy physics being used to answer questions that are usually considered the realm of high energy particle physics. For instance, precision atomic parity non-conservation experiments constrain the electroweak theory in a way that is inaccessible to particle accelerators. Another example is the search for a permanent electric dipole moment (EDM) in atoms and molecules. If an EDM were to be discovered, it would imply that the standard model of physics is incomplete, and it would point the way to a more overarching theory. The atomic measurement proposed here relates to both of these examples. The best atomic parity violation measurement uses atomic cesium in electric and magnetic fields. To extract the fundamental physics, it is necessary to disentangle the atomic physics from the atomic measurement. For about 20 years, full advantage could not be taken of the best parity violation measurement, because the atomic theory tools were not good enough. Recent theoretical advances are starting to change that, but the tools need independent validation. This project will measure a different property of cesium in an electric field, its ground state tensor polarizability (GSTP), improving the experimental knowledge of that value by a factor of at least 25. The calculations needed for the cesium parity violation result are similar to those needed to predict the GSTP, so these measurements will help validate the atomic theory with the required precision. The GSTP measurements are also similar enough to those needed for a cesium EDM search that they will be a step along the way toward completing such a measurement. The experiment will also train graduate students in a very wide range of experimental and theoretical methods.
The cesium GSTP (and ultimately the cesium EDM) will be measured using laser-cooled Cs atoms trapped in a pair of parallel 1D far-off-resonant optical lattice traps in a magnetically shielded region of space. The experiment is designed around being able to separately measure the populations of each ground state magnetic sublevel. Within the same set of atoms, direct transitions between adjacent positive magnetic sublevels can be measured at the same time as transitions between adjacent negative magnetic sublevels. In a 750 microGauss magnetic field and a 33 kV/cm electric field, these two transitions will differ by an amount that is proportional to the GSTP, ~20 Hz. The pulse-time-limited linewidth will be 1 Hz, so the line splitting that can be readily achieved with the available 108 atoms will yield ~10-4 sensitivity in a single scan. The ultimate precision will be limited by systematic affects related to the light traps. These can clearly be controlled well enough to improve on the existing 8% relative precision by a factor of 25. The fact that the new GSTP measurement directly measures transitions between ground state sublevels accounts for the large expected improvement over previous measurements, which looked for small shifts in much broader optical transitions.
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.
|Effective start/end date
|9/1/19 → 8/31/23
- National Science Foundation: $488,952.00