Tuning interaction between ultracold atoms using microwave radiation

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We performed a photo-association (PA) spectroscopy in order to know precise value of the binding energy of the molecular state. By irradiating a Bose-Einstein condensate of Rubidium 87 with a laser beam whose frequency is red detuned by 240~300GHz from D1 line of Rubidium, we observed three PA resonances whose width were on the order of 10 MHz. By comparing obtained data with literature, we found those resonances correspond to v=188~190 of 0g-. The spatial profile of dual-BEC is sensitive to the mutual scattering length (a12). In order to detect the fast switching of scattering lengths, we developed a method to observe spatial profile of dual-BEC in situ. By setting a12=80.8a0, we observed the two BECs phase separate by exciting modulation instabilities. Observed wavelength of excitation (22(4)um) matches quite well with predictions based on mean-field theory.