|M.Sc Student||Rinott Shahar|
|Subject||A Phonon Lock-In Measurement of the Critical Temperature|
for Bose-Einstein Condensation
|Department||Department of Physics||Supervisor||Professor Jeff Steinhauer|
|Full Thesis text|
We report a precise measurement of the condensate fraction as a function of temperature in a Bose-Einstein condensate. In contrast with previously reported measurements, the critical temperature agrees with the mean-field prediction. Furthermore, we see evidence that the quantum pressure in the finite condensate shift the critical temperature. We use a novel method to find the condensate fraction of a short Bragg pulse in which phonons are created using two laser beams applied for a short time. We take advantage of the fact that the condensate supports phonons, but the thermal cloud does not. We create phonons with a known spatial frequency. We obtain the condensate population from the magnitude of the Fourier transform at that frequency. This is analogous to a lock-in amplifier. In addition, we apply a similar technique above the critical temperature. There a density pattern appears and decays quickly.