Browsing by Author "Junker, Mark"

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    Intensity Dependence of Photoassociation in a Quantum Degenerate Atomic Gas
    (American Physical Society, 2003) Prodan, Ionut D.; Pichler, Marin; Junker, Mark; Hulet, Randall G.; Bohn, John L.; Rice Quantum Institute
    We have measured the intensity dependent rate and frequency shift of a photoassociation transition in a quantum degenerate gas of Li7. The rate increases linearly with photoassociation laser intensity for low intensities, whereas saturation is observed at higher intensities. The measured rates and shifts agree reasonably well with theory within the estimated systematic uncertainties. Several theoretically predicted saturation mechanisms are discussed, but a theory in which saturation arises because of quantum mechanical unitarity agrees well with the data.
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    Photoassociation in a quantum degenerate gas of lithium-7
    (2005) Junker, Mark; Hulet, Randall G.
    An experiment studying the effects of photoassociation in a quantum degenerate gas of 7Li bosons has been performed in a permanent magnet trap. A saturation in the one-photon photoassociation rate and a shift in the resonance due to the applied light field from the 2S 1/2 ground state to the 2P1/2 v ' = 83 excited molecular vibrational state have been measured and compared with theory. Limitations in the ability of the permanent magnet apparatus to study photoassociation in a Bose-Einstein condensate have prompted the development of a magneto-optical trap and an electro-magnetic trap. These new traps will assist in the process of creating a large BEC where the effects of photoassociation will be studied.
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    Single photon photoassociation in a lithium-7 BEC near a Feshbach resonance
    (2008) Junker, Mark; Hulet, Randall G.
    The rate of photoassociation (PA) determines how quickly molecules form from atoms illuminated by a resonant laser pulse. Knowledge of limits of this molecular formation rate provide a fundamental component on the maximum rate that a tightly bound ground state molecular Bose-Einstein condensate (BEC) could be formed using a two-photon transition. This molecular synthesis represents the beginning of a new era of ultracold quantum chemistry. The available Feshbach resonance in this system is an indispensable tool to increase the molecular formation rate due to PA in the anticipation of revealing these fundamental rate limits. While the rate saturates in a thermal gas, no evidence of saturation has yet been observed in a BEC. A loss of atoms due to a PA pulse tuned to the v " = 83 excited state molecular vibrational level provides the measurement of the PA rate. The rate varies by several orders of magnitude either by tuning the magnetic field near a Feshbach resonance or by adjusting the PA intensity. We measure the PA rate at magnetic fields between 550-900 Gauss in a BEC and a thermal gas, which is near the Feshbach resonance at 736 Gauss. The rapidly changing rate near the Feshbach resonance reflects the overlap between the ground state and the excited state wavefunctions. We present the first quantitative measurement of the PA rate near a Feshbach resonance. We measure the magnetic field dependence of the molecular resonance position near the Feshbach resonance. We introduce the first observation of a positive energy shift associated with photoassociation. The measured energy shift asymptotically diverges as it approaches the Feshbach resonance and agrees qualitatively with described theory at all magnetic fields. We observe intensity dependent saturation in the PA rate in a thermal gas and the measurements qualitatively agree with a unitarity limited rate. The first conclusive evidence for a suppression of the PA rate occurs for intensities above the saturation intensity. We report the first observed saturation of the PA rate in a BEC. Three separate theories present possible mechanisms for the observed saturation.