Laser-Cooling Cadmium for Optical Atomic Clock, Cold Collisions, and Quantum Gas Experiments

This project will develop experimental techniques needed to develop an atomic clock that is based on the element cadmium. The small differences in frequencies, or tick-rates, and the short time intervals that atomic clocks can measure have wide-ranging applications, including the Global Positioning System (GPS), secure financial transactions, and official U.S. and international time. Scientific applications of atomic clocks include tests of fundamental physics (such as Einstein's theory of general relativity), geodesy, long baseline interferometry, and metrology. Atomic clocks can help address questions such as whether the fundamental constants of the universe (like the ratio of the mass of an electron to the mass of a proton) change in time. The attractiveness of cadmium atoms for highly accurate clocks stems from the ability to make them relatively insensitive to the disruptive influence of thermal radiation from room-temperature surroundings, a limitation for many atomic clocks presently. An additional practical aspect is that the lasers needed to make a cadmium clock are expected to be more reliable than for other clock species with small thermal sensitivities. Cadmium also has a wide variety of isotopes (8 versions of the atom with different numbers of neutrons at its center), each of which collides with each other in different ways, opening up more possibilities to make a better clock and providing an interesting variety of fundamental physics studies. Lasers will be used to probe and control the cadmium atoms in order to better understand and quantify the aspects mentioned above and pave the way to a better atomic clock.

The project will investigate laser-cooling and trapping of fermion and boson isotopes of cadmium, particularly using the 65 kHz wide 326 nm 1S0-3P1 transition. To enhance the scattering rate in order to increase the number of trapped atoms, anticipated approaches include quenching the 3P1 state with a 350 nm laser excitation to 1D2 or using a metastable magneto-optical trap based on the 361 nm 3P2-3D3 transition. The 326nm 1S0-3P1 transition will directly yield atoms at microKelvin temperatures, which can be loaded into a far off-resonance dipole trap and subsequently loaded into a magic-wavelength optical lattice. The magic wavelength will be determined and cadmium-cadmium collisions can be studied in the dipole trap. More broadly, the project is expected to support collaborations with clocks groups around the world, for example, to evaluate the accuracies of primary atomic clocks that contribute to International Atomic Time (TAI).