Physical Review A

Measurement of elastic cross section for cold cesium collisions

S. A. Hopkins, S. C. Webster, J. Arlt, P. Bance, Simon L. Cornish, Onofrio M. Maragò, Christopher J. Foot

Published Feb 11, 2000• 39 citations

Abstract

We have measured the time taken for a magnetically trapped cloud of cold cesium atoms in the ${(F=3,m}_{F}=\ensuremath{-}3)$ ground state to rethermalize from a nonequilibrium spatial and velocity distribution. From these measurements we infer the dependences of the elastic scattering cross section on temperature and magnetic field in the ranges $1\ensuremath{-}30\ensuremath{\mu}\mathrm{K}$ and 0.05--2.0 mT, respectively. We determine a lower bound on the magnitude of the $(3,\ensuremath{-}3)+(3,\ensuremath{-}3)$ s-wave scattering length of ${940a}_{0}.$

DOI: 10.1103/physreva.61.032707

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Physical Review A

Measurement of elastic cross section for cold cesium collisions

S. A. Hopkins, S. C. Webster, J. Arlt, P. Bance, Simon L. Cornish, Onofrio M. Maragò, Christopher J. Foot

Published Feb 11, 2000• 39 citations

Publisher

Abstract

We have measured the time taken for a magnetically trapped cloud of cold cesium atoms in the

{(F=3,m}_{F}=\ensuremath{-}3)

ground state to rethermalize from a nonequilibrium spatial and velocity distribution. From these measurements we infer the dependences of the elastic scattering cross section on temperature and magnetic field in the ranges

1\ensuremath{-}30\ensuremath{\mu}\mathrm{K}

and 0.05--2.0 mT, respectively. We determine a lower bound on the magnitude of the

(3,\ensuremath{-}3)+(3,\ensuremath{-}3)

s-wave scattering length of

{940a}_{0}.

DOI: 10.1103/physreva.61.032707

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Measurement of Cs-Cs elastic scattering atT=30 μK

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arXiv:cond-mat/0305180Physical Review AJul 23, 200385 citations

We have measured the time taken for a magnetically trapped cloud of cold cesium atoms in the

{(F=3,m}_{F}=\ensuremath{-}3)

1\ensuremath{-}30\ensuremath{\mu}\mathrm{K}

and 0.05--2.0 mT, respectively. We determine a lower bound on the magnitude of the

(3,\ensuremath{-}3)+(3,\ensuremath{-}3)

s-wave scattering length of

{940a}_{0}.

{\mathit{m}}_{\mathit{F}}

=-3 on F=3,

{\mathit{m}}_{\mathit{F}}

=-3 is 1.5(4)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}12}$

{\mathrm{cm}}^{2}

, and is independent of temperature from 30 to 250 \ensuremath{\mu}K. This determination clarifies the technical requirements for attaining Bose-Einstein condensation in a magnetically trapped Cs vapor. We also study heating due to glancing collisions with 300 K background Cs atoms.

We have measured the elastic-scattering cross section of

^{87}\mathrm{Rb}

atoms in the \ensuremath{\Vert}F=1,

{\mathit{m}}_{\mathit{F}}

=-1〉 ground state at 25 \ensuremath{\mu}K. The cross section is almost purely s wave at these temperatures and has a value of (5.4\ifmmode\pm\else\textpm\fi{}1.3)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}12}$

{\mathrm{cm}}^{2}

. We have searched for the predicted Feshbach-type resonances in the elastic cross section [Tiesinga et al., Phys. Rev. A 46, 1167 (1992)] as a function of magnetic field. There are no resonances with a magnetic-field width \ensuremath{\ge}2 G over a magnetic-field range of 15--540 G.

\mathrm{Cs}{}_{2}

possesses a large scattering length (

|{A}_{3}|>35\mathrm{nm}

) and the magnitude of the second-order spin-orbit interaction is scaled to reproduce room temperature scattering data.

s

-wave scattering length

{a}_{\mathrm{s}}

for the four highest-abundance isotopes of erbium, in the magnetic field range from 0 to 5 G. We report on cross-dimensional thermalization measurements and apply the Enskog equations of change to numerically simulate the thermalization process and to analytically extract an expression for the so-called number of collisions per rethermalization (NCPR) to obtain

{a}_{\mathrm{s}}

from our experimental data. We benchmark the applied cross-dimensional thermalization technique with the experimentally more demanding lattice modulation spectroscopy and find good agreement for our parameter regime. Our experiments are compatible with a dependence of the NCPR with

{a}_{\mathrm{s}}

, as theoretically expected in the case of strongly dipolar gases. Surprisingly, we experimentally observe a dependency of the NCPR on the density, which might arise due to deviations from an ideal harmonic trapping configuration. Finally, we apply a model for the dependency of the background scattering length with the isotope mass, allowing us to estimate the number of bound states of erbium.

The s-wave scattering length for elastic collisions between

{}^{87}\mathrm{Rb}

atoms in the state

|{f,m}_{f}〉=|1,1〉

is measured in the vicinity of a Feshbach resonance near 1007 G. Experimentally, the scattering length is determined from the mean-field-driven expansion of a Bose-Einstein condensate in a homogeneous magnetic field. The scattering length is measured as a function of the magnetic field and agrees with the theoretical expectation. The width of the resonance is determined to be 0.20(3) G, the position of the zero crossing of the scattering length is found at 1007.60(3) G.