Multifrequency evaporative cooling to Bose-Einstein condensation in a highmagnetic field - art. no. 021601

We demonstrate a way to circumvent the interruption of evaporative cooling observed at high bias field for Rb-87 atoms trapped in the (F = 2,m = +2) g round state. Our scheme uses a three-frequency rf knife achieved by mixing two rf frequencies. This compensates part of the nonlinearity of the Zeeman effect, allowing us to achieve Bose-Einstein condensation where the standa rd one-frequency rf knife evaporation method did not work We are able to ge t efficient evaporative cooling, provided that the residual detuning betwee n the transition and the rf frequencies is smaller than the power broadenin g of the rf transitions at the end of the evaporation ramp.