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Journal of Physics Conference Series

All-optical production of6Li quantum gases

A. Burchianti, Jorge Amin Seman, Giacomo Valtolina, Andrea Morales, M. Inguscio, Matteo Zaccanti, G. Roati

Published Mar 18, 2015• 5 citations
Publisher

Abstract

We report efficient production of quantum gases of 6 Li using a sub-Doppler cooling scheme based on the D 1 transition. After loading in a standard magneto-optical trap, an atomic sample of 10 9 atoms is cooled at a temperature of 40 μ K by a bichromatic D 1 gray-molasses. More than 2 × 10 7 atoms are then transferred into a high-intensity optical dipole trap, where a two-spin state mixture is evaporatively cooled down to quantum degeneracy. We observe that D 1 cooling remains effective in the deep trapping potential, allowing an effective increase of the atomic phase-space density before starting the evaporation. In a total experimental cycle of 11 s, we produce weakly-interacting degenerate Fermi gases of 7 × 10 5 atoms at T/T F < 0.1 and molecular Bose-Einstein condensates of up 5 × 10 5 molecules. We further describe a simple and compact optical system both for high-resolution imaging and for imprinting a thin optical barrier on the atomic cloud; this represents a first step towards the study of quantum tunneling in strongly interacting superfluid Fermi gases.

DOI
10.1088/1742-6596/594/1/012042

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We report efficient production of quantum gases of 6 Li using a sub-Doppler cooling scheme based on the D 1 transition. After loading in a standard magneto-optical trap, an atomic sample of 10 9 atoms is cooled at a temperature of 40 μ K by a bichromatic D 1 gray-molasses. More than 2 × 10 7 atoms are then transferred into a high-intensity optical dipole trap, where a two-spin state mixture is evaporatively cooled down to quantum degeneracy. We observe that D 1 cooling remains effective in the deep trapping potential, allowing an effective increase of the atomic phase-space density before starting the evaporation. In a total experimental cycle of 11 s, we produce weakly-interacting degenerate Fermi gases of 7 × 10 5 atoms at T/T F < 0.1 and molecular Bose-Einstein condensates of up 5 × 10 5 molecules. We further describe a simple and compact optical system both for high-resolution imaging and for imprinting a thin optical barrier on the atomic cloud; this represents a first step towards the study of quantum tunneling in strongly interacting superfluid Fermi gases.
We use a gray molasses operating on the D1{D}_{1}D1​ atomic transition to produce degenerate quantum gases of 6Li^{6}\mathrm{Li}6Li with a large number of atoms. This sub-Doppler cooling phase allows us to lower the initial temperature of 10910{}^{9}109 atoms from 500 to 40 $\ensuremath{\mu}\mathrm{K}$ in 2 ms. We observe that D1{D}_{1}D1​ cooling remains effective into a high-intensity infrared dipole trap where two-state mixtures are evaporated to reach the degenerate regime. We produce molecular Bose-Einstein condensates of up to 5 $\ifmmode\times\else\texttimes\fi{}$ 10510{}^{5}105 molecules and weakly interacting degenerate Fermi gases of $7\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms at T/TF<0.1T/{T}_{F}<0.1T/TF​<0.1 with a typical experimental duty cycle of 11 s.
We use a gray molasses operating on the D[subscript 1] atomic transition to produce degenerate quantum gases of [superscript 6]Li with a large number of atoms. This sub-Doppler cooling phase allows us to lower the initial temperature of 10[superscript 9] atoms from 500 to 40 μK in 2 ms. We observe that D[subscript 1] cooling remains effective into a high-intensity infrared dipole trap where two-state mixtures are evaporated to reach the degenerate regime. We produce molecular Bose-Einstein condensates of up to 5 × 10[superscript 5] molecules and weakly interacting degenerate Fermi gases of 7×10[superscript 5] atoms at T/T[subscript F] < 0.1 with a typical experimental duty cycle of 11 s.
We report our experimental apparatus for producing 6 Li quantum gases with good optical access. Atoms are first captured in a D 2 magneto-optical trap (MOT) and subsequently cooled via a compressed MOT and D 1 gray molasses, reaching sub-Doppler temperatures as low as 70 μ K . The cold atoms are then loaded into a single-beam optical dipole trap and transported into a compact octagonal glass cell, where forced evaporative cooling is performed. We achieve quantum degeneracy, observe the formation of a molecular Bose–Einstein condensate containing 1 × 10 5 atom pairs, and demonstrate controlled tomographic imaging, thereby establishing a versatile platform for future studies of three-dimensional (3D) superfluid dynamics.
We achieve a highly degenerate and strongly interacting Fermi gas in a mixture of the two lowest hyperfine states of 6 Li by direct evaporative cooling in a high power crossed optical dipole trap. The trap is loaded from a large atom number magneto-optical trap realized by a laser system of 2.5-W intracavity-frequency-doubled light output at 671 nm. With this system, we also demonstrate the production of a molecular Bose-Einstein condensate (mBEC) of 6 Li 2 , and observe the anisotropic expansion of Fermi gases in the so-called BEC-Bardeen-Cooper-Schrieffer crossover regime.
We report the experimental production of degenerate Fermi gases of 6Li atoms in an optical dipole trap. The gray-molasses technique is carried out to decrease the atomic temperature to 57 μK, which facilitates the efficient loading of cold atoms into the optical dipole trap. The Fermi degeneracy is achieved by evaporative cooling of a two-spin mixture of 6Li atoms on the Feshbach resonance. The degenerate atom number per spin is 3.5 × 104, and the reduced temperature T/T F is as low as 0.1, where T F is the Fermi temperature of the non-interacting Fermi gas. We also observe the anisotropic expansion of the atom cloud in the strongly interacting regime.
We present an efficient scheme to implement a gray optical molasses for sub-Doppler cooling of 6Li^{6}\mathrm{Li}6Li atoms with minimum experimental overhead. To integrate the D1{D}_{1}D1​ light for the gray molasses cooling into the same optical setup that is used for the D2{D}_{2}D2​ light for a standard magneto-optical trap (MOT), we rapidly switch the injection seeding of a slave laser between the D2{D}_{2}D2​ and the D1{D}_{1}D1​ light sources. Switching times as short as 30 $\ensuremath{\mu}\mathrm{s}$ can be achieved, inferred from monitor optical beat signals. The resulting low-intensity molasses cools a sample of $N=9\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms to about 60 $\ensuremath{\mu}\mathrm{K}$. A maximum phase-space density of $\ensuremath{\rho}=1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ is observed. On the same setup, the performance of the GM is compared to that of narrow-line cooling in an ultraviolet (UV) MOT, following the procedure in Sebastian et al. [J. Sebastian, Ch. Gross, K. Li, H. C. J. Gan, W. Li, and K. Dieckmann, Phys. Rev. A 90, 033417 (2014)]. Further, we compare the production of a degenerate Fermi gas using both methods. Loading an optical dipole trap from the gray molasses yields a quantum degenerate sample with $3.3\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms, while loading from the denser UV MOT yields $2.4\ifmmode\times\else\texttimes\fi{}{10}^{6}$ atoms. Where the highest atom numbers are not a priority this implementation of the gray molasses technique yields sufficiently large samples for a comparatively low technical effort.