Guiding, Decelerating, and Trapping Polar Molecules on a Chip

Presented by Samuel Meek, Fritz Haber Institute of the Max Planck Society

During the last decade, a new technology has been developed that uses electric fields to decelerate neutral polar molecules and, in some cases, subsequently trap them. So-called Stark decelerators have enabled experiments that were impossible or infeasible with molecules before, such as lifetime measurements of long-lived metastable states, measuring inelastic collision cross sections at low but tunable energies, and high resolution spectroscopy with extremely long interaction times. Traditionally, Stark decelerators have been meter-long devices where tens of kilovolts are switched in less than a microsecond to decelerate the molecules. In the last few years, however, we have developed a microchip Stark decelerator that is capable of bringing metastable CO molecules to a standstill in a few centimeters with applied potentials of less than 200 volts. The chip contains a microstructured array of 1254 electrodes that has been configured to generate an array of local minima of electric field strength with a periodicity of 120 microns about 25 microns above the substrate. For polar molecules in certain quantum states, these electric field minima act as traps. By applying sinusoidally varying potentials to the electrodes, the minima can be moved smoothly along the array in a controllable manner, creating a series of traveling potential wells. In addition to making the experiment more compact, a microscopic Stark decelerator offers a number of other advantages, such as steep potential wells and high field gradients. This allows molecules to be positioned extremely accurately, and because the oscillation frequency in the trap is much higher, effects of quantum degeneracy can be expected at higher temperatures.