Precision Contrast Interferometry with Ytterbium Bose-Einstein Condensates

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This grant will support a project to sensitively measure the interaction between light and matter. By monitoring the change in velocity for atoms due to absorbing or emitting light, this team will measure a fundamental constant of nature known as the fine structure constant. The experiments will be performed with an atomic gas that is 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, to make an interferometer for atoms. By observing BEC interference fringes, this team will precisely measure the velocity change for atoms due to absorbing or emitting light quanta (photons). The results will provide information regarding possible refinements to the underlying theory of quantum mechanics that describes this fundamental process. The students working on this project will gain experience with lasers, electronics, and atomic physics research. The students will also gain experience analyzing data, modeling complex systems, and connecting experimental results with theory. This will form good preparation for them to join the work force in academia 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. This will be done using the contrast interferometry technique with a ytterbium BEC interferometer. This recoil frequency, combined with other measurements, will be used to accurately determine the fine structure constant, and to test the theory of quantum electrodynamics (QED). The fine structure constant is ubiquitous in nature, and QED theory extends across many sub-fields throughout physics. Improving the accuracy with which the fine structure constant is known and the precision with which QED is tested are both of fundamental importance. The contrast interferometer utilizes pulsed optical standing waves to split, manipulate, 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, this project will also advance BEC preparation, manipulation, and probing methods.