Manipulation of cold atoms by an adaptable magnetic reflector

Adaptive optics for cold atoms has been experimentally realized by applying a bias magnetic field to a static magnetic mirror. The mirror consist of a 12-mm-diameter piece of commercial videotape, having a sine wave of wavele ngth 25.4 mu m recorded in a single track across its width, curved to form a concave reflector with radius of curvature R = 54 mm. We have studied the performance of the mirror by monitoring the evolution of a 24 mu K cloud o f Rb-85 atoms bouncing on it. A uniform static external magnetic field was added to the mirror field causing a corrugated potential from which the ato ms bounce with increased angular spread. The characteristic angular distrib ution of the surface normal is mapped at the peak of the bounce for atoms d ropped from a height of R/2 and at the peak of the second bounce for a drop height of R/4. In a second experiment a time-dependent magnetic field was applied and the angular distribution of the cloud was measured as a functio n of field frequency. In this scheme we demonstrate a corrugated potential whose time-dependent magnitude behaves like a diffraction grating of variab le depth, Finally a rotating field was added to generate a corrugated poten tial that moves with a velocity given by the product of the external field rotation frequency and the videotape wavelength. This travelling grating pr ovides a new method of manipulation as cold atoms are transported across th e surface by surfing along the moving wave. Two theoretical methods have be en developed to predict the behaviour of atoms reflecting from these statio nary, variable magnitude and moving corrugated potentials. A simple analyti c theory provides excellent agreement for reflection fr om a stationary cor rugated potential and gives good agreement when extended to the case of a t ravelling grating. A Monte Carlo simulation was also performed by brute for ce numeric integration of the equations of motion fur atoms reflecting from all three corrugated potential cases.