On the 4th November 2015 we created the UK's first two-electron BEC by condensing around 105 174Yb atoms in an optical dipole trap. To create the BEC we initially loaded an Yb MOT of 5 x 108 atoms at T ~ 200 µK using the 1S0 to 3P1 cooling transition. The MOT was then cooled to T = 50 µK via intensity and detuning ramps.
The crossed dipole trap is formed by a 100 W, 1070 nm fibre laser. The dipole beams are focused to a 30 ± 2 μm and 75 ± 2 μm waist and crossed at an angle of 40˚. Initial powers of the two beams are 40 W and 12 W respectively, resulting in a trap depth of ~ 500 µK . We loaded 1.6 x 107 atoms directly from the MOT into the dipole trap with a resulting temperature of T = 50 µK after a short hold. We then evaporatively cool the atoms by ramping down the power in the dipole beams to 320 mW and 480 mW over 7 seconds. The onset of BEC occurs with N ~ 3 x 105 atoms at T ~ 250 nK.
CsYb team: (Left to right) Simon Cornish, Stephen Hopkins, Alex Guttridge