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Physical Review Letters

Spin-Singlet Bose-Einstein Condensation of Two-Electron Atoms

Yosuke Takasu, Kenichi Maki, Kaduki Komori, T. Takano, Kazuhito Honda, M. Kumakura, T. Yabuzaki, Yoshiro Takahashi

Published Jul 25, 2003• 409 citations
Publisher

Abstract

We report the observation of a Bose-Einstein condensation of ytterbium atoms by evaporative cooling in a novel crossed optical trap. Unlike the previously observed condensates, a ytterbium condensate is a two-electron system in a singlet state and has distinct features such as the extremely narrow intercombination transitions which are ideal for future optical frequency standard and the insensitivity to external magnetic field which is important for precision coherent atom optics, and the existence of the novel metastable triplet states generated by optical excitation from the singlet state.

DOI
10.1103/physrevlett.91.040404

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We report the observation of a Bose-Einstein condensation of ytterbium atoms by evaporative cooling in a novel crossed optical trap. Unlike the previously observed condensates, a ytterbium condensate is a two-electron system in a singlet state and has distinct features such as the extremely narrow intercombination transitions which are ideal for future optical frequency standard and the insensitivity to external magnetic field which is important for precision coherent atom optics, and the existence of the novel metastable triplet states generated by optical excitation from the singlet state.
We present a route to Bose-Einstein condensation devised for two-electron atoms, which do not admit practicable cooling techniques based upon narrow intercombination lines. A dipole trap for 40{}^{40}40Ca atoms in the singlet ground state is loaded from a moderately cold source of metastable triplet atoms via spatially and energetically selective optical pumping permitting 4 orders of magnitude increase of the phase-space density. Further cooling to quantum degeneracy is achieved by forced evaporation optimized to minimize three-body losses. In a combined loading and evaporation cycle of less than 3 s we are able to condense 3000 atoms.
We describe in detail our recent experiments on quantum degenerate gases of ytterbium (Yb) atoms. Up to now Bose–Einstein condensates of 174 Yb and 170 Yb, and a Fermi degenerate gas of 173 Yb have been realized by efficient evaporative cooling in a crossed far-off resonant trap. Our studies showed that the efficient escape from the trap and rapid thermalization are important for efficient evaporative cooling. We also describe some recent experiments using Yb Bose–Einstein condensates such as the achievement of a scalar atom laser, the observation of an optical coherent transient, and successful loading into an optical lattice. Finally, the future prospects using Yb quantum degenerate gases are discussed in detail.
We report the observation of a Bose-Einstein condensate in a bosonic isotope of ytterbium (170Yb)(^{170}\mathrm{Yb})(170Yb). More than 106{10}^{6}106 atoms are trapped in a crossed optical dipole trap and cooled by evaporation. Condensates of approximately 104{10}^{4}104 atoms have been obtained. From an expansion of the condensate, we have extracted the scattering length ${a}_{170}=3.6\ifmmode\pm\else\textpm\fi{}0.9\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$.
Quantum degenerate gases of alkaline-earth-like atoms are unique systems used for quantum simulation, quantum computing and studies of quantum phase transitions. We report an all-optical formation of Bose—Einstein condensates of ytterbium atoms. About 10 6 atoms of 174 Yb are transferred to a far-off-resonance optical trap (FORT) and then cooled by evaporative cooling. Phase transition occurs at the critical temperature of 520 nK. A pure condensate containing approximately 2 × 10 4 atoms has been obtained in the crossed FORT, with an atomic peak density of ∼8 × 10 14 cm −3 . The condensate lifetime exceeds 1 s.
We could recently achieve the Bose Einstein condensation (BEC) of Yb atoms. Yb differs from most of the elements that have previously been condensed, because it is a two‐electron atom with the singlet S ground state. Furthermore the Bosonic isotopes of Yb, like 174Yb which we succeeded to condensate, has no nuclear spin, so that the ground state is completely spin‐less state and hence insensitive to magnetic fields. Thus a new type of atom could join the group of atoms for BEC studies. We would like to report how we could achieve the BEC of Yb atoms.
We report on the attainment of Bose-Einstein condensation with ultracold strontium atoms. We use the (84)Sr isotope, which has a low natural abundance but offers excellent scattering properties for evaporative cooling. Accumulation in a metastable state using a magnetic-trap, narrowline cooling, and straightforward evaporative cooling in an optical trap lead to pure condensates containing 1.5 x 10(5) atoms. This puts (84)Sr in a prime position for future experiments on quantum-degenerate gases involving atomic two-electron systems.