Optical Feshbach Resonances and Coherent Photoassociation in a Strontium BEC

[摘要] The divalent electronic structure of alkaline-earth metal atoms such as strontium gives rise to metastable, excited triplet levels and narrow intercombination transitions. These have been exploited for optical clocks, powerful laser cooling techniques that are critical for achieving quantum degeneracy in strontium, and proposals for quantum information architectures and studies of novel magnetism. Metastable excited electronic states also give rise to narrow photoassociation (PA) transitions that differ in many ways from traditional PA with broad, electric-dipole-allowed transitions. In this thesis, I will introduce the use of narrow-line PA near the $$^1S_0$$-$$^3P_1$$ intercombination transition for two experiments with $$^{88}$$Sr Bose-Einstein condensates.The first experiment demonstrates the controlof the collapse and expansion of an $$^{88}$$Sr Bose-Einstein condensate using an optical Feshbach resonance (OFR) near the $$^{1}S_{0}$$-$$^{3}P_{1}$$ intercombination transition at 689,nm. Significant changes in dynamics are caused by modifications of scattering length by up to $$pm 10,a_{extrm{bg}}$$, where the background scattering length of $$^{88}$$Sr is$$a_{{extrm{bg}}} = -2,a_0$$ ($$1, a_0=0.053,$$nm).Changes in scattering length are monitored through changes in the size of the condensate after a time-of-flight measurement. Because the background scattering length is close to zero, blue detuning of the OFR laser with respect to a photoassociative resonance leads to increased interaction energy and a faster condensate expansion, while red detuning triggers a collapse of the condensate. The results are modeled with the time-dependent non-linear Gross-Pitaevskii equation.In the second experiment, we access a regime of coherent one-color photoassociation in which we observe atom-molecule Rabi oscillations and create condensates of excited-state molecules. We attain atom-molecule Rabi frequencies that are comparable to decoherence rates by driving photoassociation of atoms in an $^{88}$Sr condensate to a weakly bound level of the metastable $^{1}S_{0}$+$^{3}P_{1}$ molecular potential, which has a long lifetime and a large Franck-Condon overlap integral with the ground scattering state.Transient shifts and broadenings of the excitation spectrum are clearly seen at short times, and they create an asymmetric excitation profile that only displays Rabi oscillations for blue detuning from resonance.

[发布机构] Rice University

[效力级别] resonances