Browsing by Author "Yan, Mi"

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    Controlling Condensate Collapse and Expansion with an Optical Feshbach Resonance
    (American Physical Society, 2013) Yan, Mi; DeSalvo, B.J.; Ramachandhran, B.; Pu, H.; Killian, T.C.
    We demonstrate control of the collapse and expansion of an Sr88 Bose-Einstein condensate using an optical Feshbach resonance near the S01−P13 intercombination transition at 689 nm. Significant changes in dynamics are caused by modifications of scattering length by up to ±10abg, where the background scattering length of Sr88 is abg=−2a0 (1a0=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 optical Feshbach resonance laser with respect to a photoassociative resonance leads to increased interaction energy and a faster condensate expansion, whereas red detuning triggers a collapse of the condensate. The results are modeled with the time-dependent nonlinear Gross-Pitaevskii equation.
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    Mass scaling and nonadiabatic effects in photoassociation spectroscopy of ultracold strontium atoms
    (American Physical Society, 2014) Borkowski, Mateusz; Morzyński, Piotr; Ciuryło, Roman; Julienne, Paul S.; Yan, Mi; DeSalvo, Brian J.; Killian, T.C.
    We report photoassociation spectroscopy of ultracold 86Sr atoms near the intercombination line and provide theoretical models to describe the obtained bound-state energies. We show that using only the molecular states correlating with the 1S0+3P1 asymptote is insufficient to provide a mass-scaled theoretical model that would reproduce the bound-state energies for all isotopes investigated to date: 84Sr,86Sr, and 88Sr. We attribute that to the recently discovered avoided crossing between the 1S0+3P1 0+u (3Πu) and 1S0+1D2 0+u (1Σ+u) potential curves at short range and we build a mass-scaled interaction model that quantitatively reproduces the available 0+u and 1u bound-state energies for the three stable bosonic isotopes. We also provide isotope-specific two-channel models that incorporate the rotational (Coriolis) mixing between the 0+u and 1u curves which, while not mass scaled, are capable of quantitatively describing the vibrational splittings observed in experiment. We find that the use of state-of-the-art ab initio potential curves significantly improves the quantitative description of the Coriolis mixing between the two −8-GHz bound states in 88Sr over the previously used model potentials. We show that one of the recently reported energy levels in 84Sr does not follow the long-range bound-state series and theorize on the possible causes. Finally, we give the Coriolis-mixing angles and linear Zeeman coefficients for all of the photoassociation lines. The long-range van der Waals coefficients C6(0+u)=3868(50) a.u. and C6(1u)=4085(50) a.u. are reported.
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    Optical Feshbach Resonances and Coherent Photoassociation in a Strontium BEC
    (2013-12-03) Yan, Mi; Killian, Thomas C.; Hulet, Randall G.; Pasquali, Matteo
    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 control of 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 $$\pm 10\,a_{\textrm{bg}}$$, where the background scattering length of $$^{88}$$Sr is $$a_{{\textrm{bg}}} = -2\,a_0$$ ($$1\, a_0=0.053\,$$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.