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AIP conference proceedings

Laser cooling and trapping, Bose Einstein Condensation, the case of metastable helium

Michèle Leduc

Published Jan 1, 2005• 0 citations
Publisher

Abstract

This article first provides guide lines for the understanding of laser cooling and Bose Einstein Condensation, with a general bibliography of the domain. Some details are given about the case of an ultracold gas of helium atoms in the 23S1 metastable state. Obtention of BEC will be recalled, with discussion of the inhibition of Penning ionization collisions. Recent studies at ENS with photoassociation methods will be summarized, including the formation of giant dimers providing another example of ionization inhibition.

DOI
10.1063/1.1896494

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This article first provides guide lines for the understanding of laser cooling and Bose Einstein Condensation, with a general bibliography of the domain. Some details are given about the case of an ultracold gas of helium atoms in the 23S1 metastable state. Obtention of BEC will be recalled, with discussion of the inhibition of Penning ionization collisions. Recent studies at ENS with photoassociation methods will be summarized, including the formation of giant dimers providing another example of ionization inhibition.
The calculated upper limit ${\mathcal{K}}_{i}^{\mathrm{pol}}<~{10}^{\ensuremath{-}14}{\mathrm{cm}}^{3}/\mathrm{s}$ of the rate constant for suppressed ionization in a gas of metastable Ne(3P2)\mathrm{Ne}{(}^{3}{\mathrm{P}}_{2})Ne(3P2​) atoms in the fully aligned ∣J=2,mJ=2〉|{J=2,m}_{J}=2〉∣J=2,mJ​=2〉 state is used as input to investigate the prospects for achieving Bose-Einstein condensation (BEC). The heating rate of the trap population by secondary collisions of the hot products of the process of ionization---i.e., ground-state atoms, ions, and dimer-ions---with cold trapped metastable atoms is discussed in terms of a semiclassical model. An important step lies in limiting the depth of the magnetic trap to a value of a few millikelvin, to limit the range of small-angle scattering that contributes to heating. Also, a tight radial confinement reduces the probability for secondary collisions. At a trap depth of 10 mK, a radial dimension of $3\ensuremath{\mu}\mathrm{m},$ and a density of $2\ifmmode\times\else\texttimes\fi{}{10}^{13}{\mathrm{cm}}^{\ensuremath{-}3}$ the heating rate is $1.4\ensuremath{\mu}\mathrm{K}/\mathrm{s},$ which should be compared to the transition temperature to BEC of $0.6\ensuremath{\mu}\mathrm{K}.$ The collisional heating is dominated by ion---metastable-atom collisions, due to their long-range charge-induced dipole interaction. Keeping the evaporative cooling switched on at T=TC{T=T}_{C}T=TC​ reduces the heating a hundredfold. Using a bright beam of laser cooled neon atoms, an initial population of > 1010>~{10}^{10}> 1010 atoms can be loaded into a magneto-optical trap in one second. Tight magnetic traps are easy to achieve for metastable neon atoms, due to their magnetic moment of $3{\ensuremath{\mu}}_{B}.$ We conclude that achieving BEC is feasible for metastable neon. This also holds for triplet metastable helium, once the loading rate of traps has been improved. Finally, the semiclassical model used for calculating the heating rate is applicable to a wide range of inelastic collisions in trapped alkali gases and/or collisions with background gas.
We report the creation of a Bose-Einstein condensate using buffer-gas cooling, the first realization of Bose-Einstein condensation using a broadly general method which relies neither on laser cooling nor unique atom-surface properties. Metastable helium (\\(^4\\)He*) is buffer-gas cooled, magnetically trapped, and evaporatively cooled to quantum degeneracy. 10\\(^{11}\\) atoms are initially trapped, leading to Bose-Einstein condensation at a critical temperature of \\(5 \\mu K\\) and threshold atom number of 1.1×10\\(^6\\). This method is applicable to a wide array of paramagnetic atoms and molecules, many of which are impractical to laser cool and impossible to surface cool.
We report the creation of a Bose-Einstein condensate using buffer-gas cooling, the first realization of Bose-Einstein condensation using a broadly general method which relies neither on laser cooling nor unique atom-surface properties. Metastable helium ([superscript 4]He[superscript *]) is buffer-gas cooled, magnetically trapped, and evaporatively cooled to quantum degeneracy. 10[superscript 11] atoms are initially trapped, leading to Bose-Einstein condensation at a critical temperature of 5 μK and threshold atom number of 1.1×10 [superscript 6]. This method is applicable to a wide array of paramagnetic atoms and molecules, many of which are impractical to laser cool and impossible to surface cool.
We report the creation of a Bose-Einstein condensate using buffer-gas cooling, the first realization of Bose-Einstein condensation using a broadly general method which relies neither on laser cooling nor unique atom-surface properties. Metastable helium ((4)He*) is buffer-gas cooled, magnetically trapped, and evaporatively cooled to quantum degeneracy. 10(11) atoms are initially trapped, leading to Bose-Einstein condensation at a critical temperature of 5 microK and threshold atom number of 1.1 x 10(6). This method is applicable to a wide array of paramagnetic atoms and molecules, many of which are impractical to laser cool and impossible to surface cool.