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Physical Review A

Cold Cr52 elastic and inelastic collision-rate determination using evaporative cooling analysis

Scott V. Nguyen, Robert deCarvalho, John M. Doyle

Published Jun 15, 2007• 9 citations

Abstract

Elastic and inelastic collision-rate constants of $^{52}\mathrm{Cr}$ in the temperature range of $20\phantom{\rule{0.3em}{0ex}}\mathrm{mK}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ are inferred from the evaporative cooling of buffer gas loaded atomic chromium. Using a model that describes the dynamics of the trapped chromium cloud during evaporation, we find ${g}_{\mathrm{el}}=2.15(+2.5,\ensuremath{-}1.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}∕\mathrm{s}$ and ${g}_{\mathrm{in}}=1.36(+1.2,\ensuremath{-}0.7)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}∕\mathrm{s}$, consistent with theory but in disagreement with previously reported measurements.

DOI: 10.1103/physreva.75.062706

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Elastic and inelastic collision-rate constants of

^{52}\mathrm{Cr}

in the temperature range of

20\phantom{\rule{0.3em}{0ex}}\mathrm{mK}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1\phantom{\rule{0.3em}{0ex}}\mathrm{K}

are inferred from the evaporative cooling of buffer gas loaded atomic chromium. Using a model that describes the dynamics of the trapped chromium cloud during evaporation, we find

{g}_{\mathrm{el}}=2.15(+2.5,\ensuremath{-}1.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}∕\mathrm{s}

and

{g}_{\mathrm{in}}=1.36(+1.2,\ensuremath{-}0.7)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}∕\mathrm{s}

, consistent with theory but in disagreement with previously reported measurements.

We report the magnetic trapping and evaporative cooling of bosonic and fermionic isotopes of atomic chromium. Using a cryogenic helium buffer gas,

{10}^{12}

chromium atoms are trapped at an initial temperature of \ensuremath{\sim}1 K. The chromium atoms are then cooled adiabatically and evaporatively to temperatures as low as \ensuremath{\sim}10 mK. Elastic and inelastic

{}^{52}\mathrm{Cr}

collisional cross sections are measured over this temperature range. Prospects for simultaneously creating a

{}^{52}\mathrm{Cr}

Bose-Einstein condensate and

{}^{53}\mathrm{Cr}

Fermi degenerate gas will be discussed.

Atomic manganese

^{55}\mathrm{Mn}

and chromium

^{52}\mathrm{Cr}

are simultaneously loaded and confined in a magnetic trap. Using a cryogenic

^{3}\mathrm{He}

buffer gas,

{10}^{11}

manganese and

{10}^{12}

chromium atoms are trapped at an initial temperature of 600 mK. The buffer gas is then pumped away, thermally isolating the sample. The Mn-Cr interspecies inelastic rate constant is measured to be ${\ensuremath{\Gamma}}_{\mathrm{Mn},\mathrm{Cr}}=1.5(\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{3}∕\mathrm{s}$.

We report the magnetic trapping and evaporative cooling of bosonic and fermionic isotopes of atomic chromium. Using a cryogenic helium buffer gas, 10 1 2 chromium atoms are trapped at an initial temperature of ∼ 1 K. The chromium atoms are then cooled adiabatically and evaporatively to temperatures as low as ∼10 mK. Elastic and inelastic 5 2 Cr collisional cross sections are measured over this temperature range. Prospects for simultaneously creating a 5 2 Cr Bose-Einstein condensate and 5 3 Cr Fermi degenerate gas will he discussed.

We report on calculations of the elastic cross section and thermalization rate for collision between two maximally spin-polarized chromium atoms in the cold and ultracold regimes, relevant to buffer-gas and magneto-optical cooling. We calculate ab initio potential-energy curves for

{10}^{11}

and the van der Waals coefficient

{C}_{6}

, and construct interaction potentials between two colliding Cr atoms. We explore the effect of shape resonances on the elastic cross section, and find that they dramatically affect the thermalization rate. Our calculated value for the

s

-wave scattering length is compared in magnitude with a recent measurement. We propose that a dip in the elastic rate coefficient could be experimentally exploited to obtain an accurate value for the scattering length.