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Measurement of the Temperature Dependence of the Casimir-Polder Force

TitleMeasurement of the Temperature Dependence of the Casimir-Polder Force
Publication TypeThesis
Year of Publication2007
AuthorsObrecht, JM

A measurement of the temperature dependence of the Casimir-Polder force is presented along with subsequent measurements of electric fields near surfaces. These measurements were obtained by studying the effects of surface forces on the collective oscillations of a magnetically trapped 87Rb Bose-Einstein condensate (BEC).

In the first part of this thesis, the measurement of the Casimir-Polder force is described. In this experiment, the BEC was placed a few microns from a dielectric substrate and excited into its dipole oscillation. Changes in the collective oscillation frequency resulted from spatial variations in the surface-atom force. The temperature dependence of this force was observed as a threefold increase in its strength as the substrate was heated from 300 K to 600 K, in agreement with theory.

The second part of this thesis deals with measurements that were made of electric fields emanating from surface adsorbates. An alternating external electric field was applied that adds to (or subtracts from) the adsorbate’s field in such a way as to resonantly drive the BEC into a mechanical dipole oscillation. The growth rate of the oscillation’s amplitude provides information about the magnitude and sign of the adsorbate’s field gradient. Using this technique, we were able to reconstruct vectorially the electric field produced by surface contaminants and account for their systematic effects. Lastly, we show that baking the substrate can reduce the electric fields emanating from adsorbates, and that the mechanism for reduction is likely surface diffusion, not desorption.

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