We have achieved Bose-Einstein condensation of 40 Ca, the first for an alkaline earth element. The influence of elastic and inelastic collisions associated with the large ground-state s-wave scattering length of 40 Ca was measured. From these findings, an optimized loading and cooling scheme was developed that allowed us to condense about 2·10 4 atoms after laser cooling in a two-stage magnetooptical trap and subsequent forced evaporation in a crossed dipole trap within less than 3 s. The condensation of an alkaline earth element opens novel opportunities for precision measurements on the narrow intercombination lines as well as investigations of molecular states at the 1 S-3 P asymptotes.PACS numbers: 03.75.Hh, 67.85.HjThe first Bose-Einstein condensate (BEC) of a dilute quantum gas in 1995 has opened completely new avenues in physics. In subsequent years this quantum degenerate state could be reached with different species (for a recent list of references see, e. g., [1]). By far most research has been performed on alkali atomic and molecular BECs apart from hydrogen, metastable helium, chromium, and ytterbium. So far, no member of the alkaline earth elements could be brought to quantum degeneracy despite considerable effort [2,3]. The alkaline earth elements have unique properties, e. g., their narrow intercombination transitions or their ground state without a magnetic moment. Due to the non-degenerate ground state in 40 Ca and in the other alkaline earth elements, the associated simpler molecule structure allows for more accurate investigations of collisions [4,5]. Moreover, the vanishing magnetic moment in the ground and excited state will allow for novel applications in atom interferometry not hampered by phase shifts due to magnetic fields. Calcium has a particularly large ground state scattering length that not only made it interesting but also difficult to realize a BEC.Calcium (like the other alkaline earth elements) shares these properties with ytterbium which has a similar electronic structure [6] but has a five hundred-fold larger line width of the 1 S 0 -3 P 1 intercombination transition. This 370 Hz line width at 657 nm made calcium for some time the optical frequency standard with the lowest uncertainty in the visible [7]. Both technologies, optical frequency metrology and the generation of a BEC, can now be combined for novel applications.In this letter we report on the preparation of a 40 Ca BEC. Starting point for our experiment is a magnetooptical trap (MOT) on the 1 S 0 -1 P 1 transition in the singlet system. The vanishing ground-state magnetic moment prevents sub-Doppler cooling of 40 Ca in a MOT. To cool the atoms further we use a second MOT stage on the narrow intercombination line 1 S 0 -3 P 1 allowing for temperatures in the MOT as low as 15 µK. For efficient cooling we increase the scattering rate of this transition by quenching the upper state [8]. During both MOT stages an optical dipole trap is overlapped with the MOT. In order not to interfere with the narrow line cooling we choo...
We performed measurements of the Shubnikov-de Haas effect (SdH) and of the Quantum-Hall effect (QHE) at GaInAs quantum wells confined by AlInAs barriers. At odd filling factors (1 and 3), the two-dimensional electron system (2DES) of the quantum well is partially spin-polarized, leading to an enhanced effective Landé factor g*. In this case, asymmetric and hysteretic SdH-oscillations were predicted. At filling factor 1 (higher spin polarization) the asymmetry could be confirmed experimentally. At filling factor 3, the predicted asymmetry could be observed at a sample of higher electron density in tilted magnetic fields above 12 T. A hysteresis was not resolvable due to a reduced spin polarization
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