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Cooling and trapping Strontium atoms

We performed the simultaneous trapping of two isotopes (86Sr and 88Sr) in the red MOT (N.Poli et al. Phys. Rev. A 71, 061403(R) (2005)). Thanks to the low temperature obtained in the red MOT, such isotopic mixture is efficiently transferred into a FORT. We observe fast interspecies thermalization in the dipole trap which allows one to set a lower bound of 70aB on the 86Sr-88Sr elastic cross section.

Further we experimentally investigated two-body and three-body collisions in ultra-cold strontium samples. The elastic cross section of 86Sr and 88Sr were measured. The value for 3-body recombination rate of 86Sr and the upper bound of 3-body recombination rate of 88Sr were set. Based of this study a novel optical-sympathetic cooling method in isotopic mixtures is demonstrated. Without evaporative cooling, a phase-space density of 6 10-2 is obtained with a high spatial density (G. Ferrari et al., Phys. Rev. A 73, 023408 (2006)).

With a forced evaporation after the sympathetic cooling, we have obtained a 88Sr sample at phase-space density of 0.2, that is the highest value reported so far for an alkali-earth metal atom.