Contrast Interferometry with Quantum Degenerate Ytterbium Gases

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This grant will support a project to sensitively measure the interaction between light and matter. The experiments will be performed on an atomic gas cooled to very low temperatures in the laboratory, at which point it transforms into an exotic state called a Bose-Einstein condensate (BEC). Like a laser beam, the BEC can be split into multiple parts and then recombined. If the different parts interact differently with light, then this shows up in the properties of the recombined BEC. By using light pulses to split, recombine, and then observe BECs, the group will precisely measure the strength of the light-matter interaction. Their results will provide information regarding possible refinements of the underlying theory of this fundamental process. The atom they are studying (Ytterbium) has potential applications in the development of improved time standards for the global positioning system (GPS) and in the development of quantum computers; both of these efforts involve the sorts of laser-atom control techniques that the group is helping to advance in this project. The students working on the project will gain experience in experimental methods involving atoms, lasers, and electronics, and also be involved in data analysis, modeling, and connecting experimental results with theory. This will form good preparation for them to join the work force in academics and industry as part of the next generation of scientists and engineers. The kinetic energy of an atom recoiling due to absorption of a single photon will be precisely measured as a frequency, by further development of the group's demonstrated contrast interferometry technique with ytterbium BECs. This recoil frequency, combined with other measurements, will accurately determine the fine structure constant alpha, and test the theory of quantum electrodynamics (QED). The fine structure constant is ubiquitous in nature, and QED theory extends across various physics sub-fields. Continued refinement is of fundamental importance. The contrast interferometer utilizes pulsed optical standing waves to split and recombine BECs. The interferometer signal is obtained by monitoring the contrast of the resultant interference pattern via reflection of an optical traveling wave. In addition to testing QED, the group's interferometry technique will advance BEC manipulation methods, and will be used to study many-body phenomena, such as the BEC phase transition.