We are pursuing two experiments at Amherst College. The first project is a continuation of our experiment to test Local Lorentz Invariance (LLI) and CPT invariance. LLI is the notion that the laws of physics are the same in all locally inertial frames and independent of their orientation in space. CPT is the product of the discrete symmetries charge conjugation, parity and time. No violation of either LLI or CPT has ever been observed. Much of our understanding of fundamental physics would have to be radically altered if a violation is observed. We compare the relative precession frequencies of Hg and Cs magnetometers as a function of the orientation of an applied magnetic field with respect to the "fixed stars". This comparison is sensitive to LLI violating couplings between a preferred universal frame and the electron, neutron and proton spins. With our recently completed experiment, we have placed new limits on several LLI violating terms. It has been pointed out that these limits may actually probe physics on the Planck scale, where String Theory suggests that violations might occur. We indend to replace the magnetometers with ones of a new design that should be at least a factor of twenty more sensitive. At this level, the experiment will provide the most stringent heavy-atom test of several possible mechanisms for violating LLI and CPT.
In our second project we are exploring the possibility of laser cooling thallium fluoride (TlF) using a transition between the v=0, J=1 of the ground state to the v'=0,J'=1 state of the triplet B state. Methods to cool molecules using lasers have only recently achieved some level of success. The difficulty with laser-cooling of molecules stems from the myriad of possible states available for decay. It is hard to find a cycling transition which will allow the tens of thousands of absorption/emission cycles that are required to achieve significant cooling. In recent work, we have demonstrated that with only one cooling laser and one repump laser it should be possible to achieve several thousand photon cycles on this transition without significant loss to other levels. This should allow transverse cooling and collimation of a cryogenic beam. Here, we intend to make precision measurements of the other critical Franck-Condon factors. Their determination will tell us precisely how many repump lasers would be required to bring a cryogenic beam of the TlF to rest. We also intend to measure the B state hyperfine structure (HFS) and isotope shifts. The HFS plays a critical role in determining the rate of loss to other rotational levels. If the laser cooling and trapping of TlF is possibile, this would open up the possibility of performing a high-precision search for the electric dipole moment of the Tl nucleus. Such an experiment is sensitive to the Schiff moment of the Tl nucleus which is in turn sensitive to the proton edm and time-reversal violation in the nuclear interaction.
Both of these projects have as their long-term goal the investigation of the fundamental symmetries of nature. Even though they are relatively modest table-top experiments, they have important possible implications for particle physics. The local Lorentz invariance experiment can provide limits on String Theory while a future thallium fluoride (TlF) electric-dipole moment experiment would test time-reversal symmetry in the proton and in the nuclear interaction. These projects, using the precision techniques of atomic and laser physics, provide a broad and flexible training for future scientists. The TlF experiment will expose our students to the exciting and emerging field of the laser-cooling of molecules. This project nicely compliments both the BEC work being done here by Prof. David Hall and the uv laser development that is being pursued by our new assistant Professor David Hanneke as part of his work on trapping single ions. Our fundamental symmetries experiments at Amherst have drawn many talented undergraduates into careers in physics over the last 29 years. This project will continue our tradition of pursuing state of the art experiments while providing exciting research opportunities and valuable training for undergraduates.
