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arXiv:1207.4713 · Physical Review A

Direct evaporative cooling of 39 K atoms to Bose-Einstein condensation

Manuele Landini, Sanjukta Roy, G. Roati, Andrea Simoni, M. Inguscio, Giovanni Carlo Modugno, M. Fattori

Published Sep 20, 2012• 41 citations
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Abstract

We report the realization of a Bose-Einstein condensate of ${}^{39}$K atoms without the aid of an additional atomic coolant. Our route to Bose-Einstein condensation comprises sub-Doppler laser cooling of large atomic clouds with more than ${10}^{10}$ atoms and evaporative cooling in an optical dipole trap where the collisional cross section can be increased using magnetic Feshbach resonances. Large condensates with almost ${10}^{6}$ atoms can be produced in less than 15 s. Our achievements eliminate the need for sympathetic cooling with Rb atoms, which was the usual route implemented until now due to the unfavorable collisional property of ${}^{39}$K. Our findings simplify the experimental setup for producing Bose-Einstein condensates of ${}^{39}$K atoms with tunable interactions, which have a wide variety of promising applications, including atom interferometry to studies on the interplay of disorder and interactions in quantum gases.

DOI
10.1103/physreva.86.033421

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We describe an experimental setup and the cooling procedure for producing 39K^{39}\mathrm{K}39K Bose-Einstein condensates of over $4\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms. Condensation is achieved via a combination of sympathetic cooling with 87Rb^{87}\mathrm{Rb}87Rb in a quadrupole-Ioffe-configuration (QUIC) magnetic trap and direct evaporation in a large-volume crossed optical dipole trap, where we exploit the broad Feshbach resonance at 402 G to tune the 39K^{39}\mathrm{K}39K interactions from weak and attractive to strong and repulsive. In the same apparatus we create quasipure 87Rb^{87}\mathrm{Rb}87Rb condensates of over $8\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms.
We report the all-optical production of Bose-Einstein condensates (BEC) of 39K^{39}\mathrm{K}39K atoms. We directly load $3\ifmmode\times\else\texttimes\fi{}{10}^{7}$ atoms in a large volume optical dipole trap from gray molasses on the D1 transition. We then apply a small magnetic quadrupole field to polarize the sample before transferring the atoms in a tightly confining optical trap. Evaporative cooling is finally performed close to a Feshbach resonance to enhance the scattering length. Our setup allows one to cross the BEC threshold with $3\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms every 7 s. As an illustration of the interest of the tunability of the interactions we study the expansion of Bose-Einstein condensates in the one-dimensional to three-dimensional crossover.
We have investigated the collisional properties of 41K^{41}\text{K}41K atoms at ultracold temperatures. To demonstrate the possibility of using 41K^{41}\text{K}41K as a coolant, a Bose-Einstein condensate of 41K^{41}\text{K}41K atoms in the stretched state (F=2,mF=2)(F=2,{m}_{F}=2)(F=2,mF​=2) was created by direct evaporative cooling in a magnetic trap. An upper bound of the three-body loss coefficient for atoms in the condensate was determined to be $4(2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}29}\text{ }{\text{cm}}^{\ensuremath{-}6}\text{ }{\text{s}}^{\ensuremath{-}1}$. A Feshbach resonance in the $F=1,\text{ }{m}_{F}=\ensuremath{-}1$, state was observed at 51.35(10) G, which is in good agreement with theoretical prediction.
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