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Guglielmo Tino's group

Ultracold atoms and precision measurements

Home Ultra-cold Strontium
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More info about Strontium

Strontium is an alkaline earth metal, its atomic number is 38. Strontium is a soft silver-white metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. Due to its extreme reactivity to air, this element occurs naturally only in compounds with other elements, as in the minerals strontianite and celestite.

Strontium has four stable, naturally occurring isotopes: 84Sr (0.56%), 86Sr (9.86%), 87Sr (7.0%) and 88Sr (82.58%). Only 87Sr is radiogenic; it is produced by decay from the radioactive alkali metal 87Rb. Thus, there are two sources of 87Sr in any material: that formed during primordial nucleo-synthesis along with 84Sr, 86Sr and 88Sr, as well as that formed by radioactive decay of  87Rb. The ratio 87Sr / 88Sr is the parameter typically reported in geologic investigations; ratios in minerals and rocks have values ranging from about 0.7 to greater than 4.0. Because strontium has an atomic radius similar to that of calcium, it readily substitutes for Ca in minerals.

Recently experimental studies of ultra-cold strontium attracted a lot of attention. Several groups exploit strontium atoms 87Sr, 88Sr to realize an atomic clocks: http://jilawww.colorado.edu/YeLabs, http://www.amo.t.u-tokyo.ac.jp, http://lne-syrte.obspm.fr. Due to its ultra-narrow 1S0=>3P0 transition strontium is a promising candidate for a frequency standard. Moreover strontium atoms are used in an experimental atomic clock with record-setting accuracy (A.D. Ludlow et al., Science 28 March 2008 319: 1805-1808).

Considerable interest is devoted to possible achievement of Bose condensation (BEC) of strontium. Up to now no alkali-earth elements were Bose condensed. Strontium is promising candidate for BEC because of possibility to reach high phase-space density by laser cooling. However evaporative cooling of cold strontium is challenging due to high 3-body collision rate for 86Sr, and vanishingly small elastic cross section for 88Sr. Nevertheless BEC of 88Sr remains an interesting subject, since 88Sr represents almost ideal gas due its negligible atomic interaction.

Couple of groups studies strontium ultra-cold plasma:
http://massey.dur.ac.uk/research/strontium/strontium.html, http://www.owlnet.rice.edu/~killian. Fundamental interest in these systems stems from the possibility of creating strongly coupled plasmas. However collective modes, recombination and thermalization have also been studied.

Strontium atoms have an electronic level structure particularly suited for applications in matter-wave interferometry. For example 88Sr has a zero orbital, spin, and nuclear angular momentum, which makes it insensitive to stray electric and magnetic fields. In addition 88Sr has a negligible atom-atom interaction. These factor makes 88Sr remarkably robust against the most typical decoherence processes (G. Ferrari et al., Phys. Rev. Lett. 97, 060402 (2006)). Therefore 88Sr is a particularly good probe to study external forces.