arXiv:cond-mat/0509286 · Physical Review Letters

Accurate Determination of the Scattering Length of Metastable Helium Atoms Using Dark Resonances between Atoms and Exotic Molecules

Steven Moal, M. Portier, J. Kim, Julien Dugué, Umakant D. Rapol, Michèle Leduc, Claude N. Cohen-Tannoudji

Published Jan 20, 2006• 92 citations

Abstract

We present a new measurement of the $s$-wave scattering length $a$ of spin-polarized helium atoms in the $2\text{ }^{3}S_{1}$ metastable state. Using two-photon photoassociation spectroscopy and dark resonances, we measure the energy ${E}_{v=14}=\ensuremath{-}91.35\ifmmode\pm\else\textpm\fi{}0.06\text{ }\text{ }\mathrm{MHz}$ of the least-bound state $v=14$ in the interaction potential of the two atoms. We deduce a value of $a=7.512\ifmmode\pm\else\textpm\fi{}0.005\text{ }\text{ }\mathrm{nm}$, which is at least 100 times more precise than the best previous determinations and is in disagreement with some of them. This experiment also demonstrates the possibility to create exotic molecules binding two metastable atoms with a lifetime of the order of $1\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$.

DOI: 10.1103/physrevlett.96.023203

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arXiv:cond-mat/0509286 · Physical Review Letters

Accurate Determination of the Scattering Length of Metastable Helium Atoms Using Dark Resonances between Atoms and Exotic Molecules

Steven Moal, M. Portier, J. Kim, Julien Dugué, Umakant D. Rapol, Michèle Leduc, Claude N. Cohen-Tannoudji

Published Jan 20, 2006• 92 citations

arXiv HTML PDF

Abstract

We present a new measurement of the

s

-wave scattering length

a

of spin-polarized helium atoms in the

2\text{ }^{3}S_{1}

metastable state. Using two-photon photoassociation spectroscopy and dark resonances, we measure the energy

{E}_{v=14}=\ensuremath{-}91.35\ifmmode\pm\else\textpm\fi{}0.06\text{ }\text{ }\mathrm{MHz}

of the least-bound state

v=14

in the interaction potential of the two atoms. We deduce a value of

a=7.512\ifmmode\pm\else\textpm\fi{}0.005\text{ }\text{ }\mathrm{nm}

, which is at least 100 times more precise than the best previous determinations and is in disagreement with some of them. This experiment also demonstrates the possibility to create exotic molecules binding two metastable atoms with a lifetime of the order of

1\text{ }\text{ }\ensuremath{\mu}\mathrm{s}

DOI: 10.1103/physrevlett.96.023203

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A new measurement of s-wave scattering length of metastable helium atoms by photoassociative spectroscopy

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arXiv:1404.1759Physical Review LettersJun 25, 201436 citations

Photo-Mechanical Effect of Photoassociation : a New Method to Measure the Scattering Length of Ultracold Metastable Helium Atoms

J. Kim, S. Moat, M. Portier +1 more

Conference on Lasers and Electro-Optics Pacific Rim (CLEO-PR)Aug 1, 20070 citations

We present a new measurement of the

s

-wave scattering length

a

of spin-polarized helium atoms in the

2\text{ }^{3}S_{1}

metastable state. Using two-photon photoassociation spectroscopy and dark resonances, we measure the energy

{E}_{v=14}=\ensuremath{-}91.35\ifmmode\pm\else\textpm\fi{}0.06\text{ }\text{ }\mathrm{MHz}

of the least-bound state

v=14

in the interaction potential of the two atoms. We deduce a value of

a=7.512\ifmmode\pm\else\textpm\fi{}0.005\text{ }\text{ }\mathrm{nm}

1\text{ }\text{ }\ensuremath{\mu}\mathrm{s}

We describe two-photon photoassociation (PA) experiments operated in an ultracold gas of metastable

^{4}\mathrm{He}^{*}

atoms in the

2\phantom{\rule{0.2em}{0ex}}^{3}S_{1}

state. Atom-molecule dark resonances as well as Raman signals provide information on the exotic molecule in the least bound vibrational

J=2

v=14

state of the $^{5}\ensuremath{\Sigma}_{g}^{+}$ interaction potential of two spin-polarized metastable atoms. The physical origin of the various two-photon PA signals is first discussed. Their linewidths are interpreted in terms of processes limiting the lifetime $\ensuremath{\tau}$ of the exotic molecule. A value of $\ensuremath{\tau}=1.4\ifmmode\pm\else\textpm\fi{}0.3\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}\mathrm{s}$ is found, which significantly differs from two recent calculations of the Penning ionization rate induced by spin-dipole coupling [T. J. Beams et al., Phys. Rev. A 74, 014702 (2006); M. Portier and G. V. Shlyapnikov (unpublished)]. The limitation of $\ensuremath{\tau}$ by atom-molecule inelastic collisions is investigated and ruled out.

The properties of the least-bound vibrational level

(v=14)

of the $^{5}\ensuremath{\Sigma}_{g}^{+}$ state formed during the ultracold collision of two spin-polarized metastable

2\phantom{\rule{0.2em}{0ex}}^{3}S_{1}

helium atoms are crucial to studies of photoassociation spectroscopy of metastable helium. We report a calculation of the autoionization lifetime ${\ensuremath{\tau}}_{g}$ of this state induced by spin-dipole coupling of the $^{5}\ensuremath{\Sigma}_{g}^{+}$ state to the $^{1}\ensuremath{\Sigma}_{g}^{+}$ state from which Penning and associative ionization processes are highly probable. We find ${\ensuremath{\tau}}_{g}\ensuremath{\approx}150\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}\mathrm{s}$, significantly larger than the recent experimental estimates of $(0.5\ensuremath{-}3)\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}\mathrm{s}$.

We have measured the forbidden $2\text{ }^{3}{S}_{1}\ensuremath{\rightarrow}2\text{ }^{1}{P}_{1}$ transition at 887 nm in a quantum degenerate gas of metastable

^{4}\mathrm{He}

atoms confined in an optical dipole trap. The determined transition frequency is 338 133 594.4 (0.5) MHz, from which we obtain an ionization energy of the

2\text{ }^{1}{P}_{1}

state of 814 709 148.6 (0.5) MHz. This ionization energy is in disagreement by $>3\ensuremath{\sigma}$ with the most accurate quantum electrodynamics calculations available. Our measurements also provide a new determination of the lifetime of the

2\text{ }^{1}{P}_{1}

state of $0.551\text{ }(0.004{)}_{\text{stat}}\text{ }{(}_{\ensuremath{-}0.000}^{+0.013}{)}_{\text{syst}}\text{ }\text{ }\mathrm{ns}$, which is the most accurate determination to date and in excellent agreement with theory.