We are developing methods to precisely measure the rotation frequencies of molecular ions.
Molecular ions (charged molecules) are a unique phase of matter. They are naturally found in star-forming regions called molecular clouds, in outer space. When these molecular ions rotate, they emit microwave radiation, which can be detected using radio telescopes on earth. The light emitted by molecules in space conveys information about the environment of these molecules in space, and as well, whether the fundamental laws of physics (electromagnetism, the values of fundamental constants, and so on) operate the same way in widely separated parts of the universe. Our aim is to measure the frequency of the microwave radiation emitted by molecular ions with an accuracy better than 1 part per billion.
Trapping of molecular ions is required in order to confine the ions for a long time and measure their, which improves the precision of determining their frequency. Cooling the ions is helpful as it reduces the Doppler shift of the radiation emitted by the molecules, and allows us to measure their frequencies more accurately. We trap ions in a radio-frequency (rf) trap, and cool them down through collisions with neutral gas molecules ("buffer gas cooling"), and through interactions with laser-cooled atomic ions ("sympathetic cooling").