Bose-Einstein condensation in micro-potentials for atom interferometry

Interferometry with atoms is a young discipline of physics. The ¯rst interfer- ometers were realised in the early 1990s, using light pulses as beamsplitters in momentum space. Recent developments in atom optics have led to new proposals for interferometers, where the splitting takes place spatially. Mag- netic and optical traps are both suited for this kind of interferometer if a well de¯ned and highly controllable trap is realised. In this thesis results from two experiments that in principle allow the creation of such traps are presented. After reviewing the principles and techniques of atom optics necessary for the understanding of this thesis, a theoretical discussion about the spatial single atom interferometer in a double well potential follows. It is shown that within reasonable limits the system can be reduced to two levels and solved by the Bloch equations. Using the realistic case of a not perfectly symmetric double well potential allows an understanding of the physics behind such an interferometer: how phase is accumulated and how localisation of the atoms leads to the loss of the interferometric signal. Then two experiments are presented. One experiment was newly built up as part of this thesis: it uses a novel hybrid atom chip' with a combination of a magneto-optical ¯lm and current-carrying structures to produce the magnetic trapping potentials. This experiment allowed 5¢108 87Rb atoms to be captured in a magneto-optical trap, where the atom-chip's surface acts as a mirror. The atoms were then transferred into a purely magnetic trap which was created by current carrying structures on the chip. From there on, RF radiation enforced evaporative cooling, so that a quantum degenerate Bose-Einstein condensate of up to 105 atoms was created. It was also shown that the magneto-optical ¯lm is able to hold and trap the atoms. In the second experiment atoms are trapped in the spatially varying inten- sity of light of 1.03 ¹m wavelength. This experiment used an existing set-up as a basis and was modi¯ed and improved for this new project. This experiment starts with 109 87Rb atoms in a 6-beam magneto-optical trap. After examining and optimising the loading process, 1:5 ¢ 105 atoms could be loaded directly from the Magneto-optical trap into the optical dipole potential of two crossed laser beams at 1.03 ¹m. Evaporative cooling was demonstrated though the phase transition to quantum degeneracy was not reached.