Bose-Einstein condensates in magnetic double well potentials

Abstract

This thesis presents two realizations of magnetic double well potentials for Bose-Einstein condensates (BECs) on atom chips. One approach utilizes static magnetic traps, created by current carrying micro wires, manipulating the atoms close to the chip surface. As in all other atom chip experiments, cold atom clouds are found to break up to pieces in the vicinity of the trapping structure. A careful study of the underlying magnetic potential could attribute this fragmentation to current deviations, caused by corrugation of the wire edges. To avoid this effect, a new fabrication technique (electron beam lithography, gold evaporation) was employed to create 700nm cross section wires of significantly improved quality. A BEC was created and successfully transferred to the sub-micron structure, generating the double well. The general qualification of the device could be demonstrated by splitting cold thermal atomic clouds. However, numerous technical problems do yet prevent us from performing the experiment with BECs. The second approach pursued in this thesis combines static magnetic traps with oscillating (RF) magnetic fields and realizes a double well in the emerging adiabatic dressed potential. This scheme can be realized far from the chip surface, fragmentation does not occur and Bose-Einstein condensates could be split successfully. We realize a matter wave interferometer by recombining the two clouds in free expansion. The arising interference patterns reveal a narrow distribution of the relative phase, indicating a coherent splitting process. We monitor the phase evolution throughout and after the splitting and control it by deliberately unbalancing the double well.