Doubledegenerate BoseFermi mixture of StrontiumFermionic atoms with two valence electrons, as ^{87}Sr, ^{171}Yb, and ^{173}Yb, have a ground state that possesses only the nuclear magnetic moment. ^{87}Sr has a nuclear spin of 9/2, which is the largest of these. This nuclear spin is at the heart of proposals for quantum computation and simulation. It allows the protected storage of quantum information, which can then be manipulated using the rich electronic structure of those twoelectron elements. It enables also quantum simulations that are highly interesting but impossible to perform using alkali atoms, as the simulation of SU(10) symmetric lattice spin models. For all these applications, quantum degenerate samples prepared in a well defined initial state are required.
Figure 1: Azimuthally averaged density distributions of a degenerate Fermi gas at T/TF = 0.28 (left) and a thermal fermionic cloud at T/TF = 0.95 (right) after 10 ms of free expansion. FermiDirac distributions (solid red line) fit both measurements well. For low T/TF, the FermiDirac fit deviates from both a Gaussian fit (dotted blue line), and a Gaussian fit to the wing of the distribution (dashed grey line). For T/TF = 0.95, the difference between the three fits is barely visible.
We achieve a degeneracy of T/TF = 0.30(5) with 2 x 10^{4} ^{87}Sr atoms at the end of the evaporation. The degenerate Fermi gas is accompanied by an almost pure ^{84}Sr BEC of 10^{5} atoms. Figure 2 illustrates the difference in the density distribution of a BEC and a Fermi gas in thermal equilibrium after free expansion.
Figure 2: Timeofflight absorption images of a nearly pure ^{84}Sr BEC and a ^{87}Sr Fermi gas at T/TF of 0.45 after 15 ms expansion. The BEC expansion is mean field driven and leads to an inverted aspect ratio. The momentum distribution of the fermionic sample is much broader than the one of the bosonic sample because of the Pauli exclusion principle forcing the fermions to higher momentum states.
The TeamMeng Khoon Tey, Simon Stellmer, Rudolf Grimm and Florian Schreck
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