Atom optics with magnetic surfaces: II. Microscopic analysis of the `floppy disk' mirror

Abstract

In a recent experiment we studied cold rubidium atoms bouncing on a magnetic mirror made from a flexible computer disk with sinusoidal magnetization. The motion was well described by a model in which the mirror was a perfect specular reflector, but complete agreement with the data required the reflecting surface to be slightly corrugated. Here we explore the physical origins of the corrugation both theoretically and experimentally.First, we develop a theory relating the reflecting force on the atoms to the magnetization of the mirror, taking into account the finite thickness of the magnetic film. We find that if the signal on the floppy disk is not harmonic the atoms appear to have been reflected from a corrugated surface, as observed in our recent experiment. Next, we describe magnetic force microscope measurements which allow us to determine the distortion on the disk and hence to quantify its effect on the reflected atoms. We show that recording nonlinearity is indeed a major cause of the mirror roughness. We also consider other sources of roughness and identify an important effect associated with the boundaries between recorded tracks. Agreement between our experiment and theory suggests that we have identified the limiting factors in a real atom-optical element made from a floppy disk. At present the angular resolution of the mirror is approximately 35 mrad for atoms dropped from a height of 4 cm. We discuss how this can be improved to reach a level of 5 mrad or better.

Cold atoms in videotape micro-traps

“…These include audiotape [1], floppy disks [2,3,4], videotape [5,6], magneto-optical films [7,8,9], and hard disks [10]. Using standard lithographic techniques, it is also possible to make small patterns of current carrying wires for the same purpose [11,12].…”

Sub-micron period lattice structures of magnetic microtraps for ultracold atoms on an atom chip

“…These values are close to the result from the SEM analysis (figure 4b) confirming the quality of the periodicity of the structure. Some of the difference between the two measurements comes from the calibration of the spatial dimensions in the MFM apparatus or from high harmonic terms that we have neglected in this analysis [53].…”

Magnetic Waveguide for Trapping Cold Atom Gases in Two Dimensions

“…At a distance z above the surface, the magnitude of the field is B max exp͑22p z͞l͒ [16]. Such surfaces have been developed recently for reflecting and focusing slow atomic beams through the Zeeman interaction, which is able to retroreflect atoms dropped from heights of many centimeters [17][18][19][20][21]. Here, we show how the Zeeman shift in sublevel F 3, m F 22, labeled f in Fig.…”

“…The quantized vibration of an atom in this trap has a minimum width of 9 nm, proportional to l 1͞2 ͑DnM͒ 21͞4 and independent of B max . The spacing of low-lying vibrational levels in this potential is proportional to ͑Dn͞M͒ 1͞2 l 21 and, in this example, equals 2 MHz ͑100 mK͒. Considering the potential to be a planar waveguide for atomic de Broglie waves, this is also the spacing of low-order modes.…”