Our group explores many facets of ultracold strontium, emphasizing precision measurement and quantum manipulation. We started a study of ultra-cold Sr at year 2002. Our first experiment was realized with a thermal atomic beam of strontium and a pre-stabilized diode laser tuned to the narrow 1S0?3P1 intercombination line (689 nm) of the bosonic 88Sr isotope. We report the first absolute frequency measurement of the 1S0=>3P1 intercombination line of 88Sr (G.Ferrari et al., Phys. Rev. Lett. 91, 243002 (2003)), obtained with a relative uncertainty of 2.3 10-11, which represents an improvement by more than 4 orders of magnitude with respect to previous data.

In next few years we have realized an apparatus for the production of Sr MOT. The apparatus includes a source of an atomic beam, a vacuum apparatus for slowing and trapping atomic strontium and all the necessary laser sources. Strontium has a strong broad 1S0?3S1 transition in the blue (461 nm). This transition we use for the Zeeman slower and for a conventional magneto-optical trap (MOT), so called blue MOT. The narrow intercombination transition 1S0=>3P1 at 689 nm is used for a second stage cooling, so called red MOT. Due to narrow linewidth (7.6 kHz) of the transition atoms can be cooled below the classical recoil limit in the red MOT. These two stage MOT technique allow us to obtain a large atomic sample of strontium at sub-?K temperature without using a sub-Doppler and evaporative cooling.

Fig. 1: Electronic level structure of srontium

Using this two stage cooling procedure we routinely obtain few millions of 88Sr atoms at temperature bellow 1 ┬ÁK. The atomic sample usually is loaded in a far-off resonant optical dipole trap (FORT) or in an optical lattice for further manipulations. Low temperature, large number of atoms and life-time in order 7 seconds give us a good initial point for a research using ultra-cold strontium.


Fig. 2: Experimental setup, main chamber with Blue MOT