Enhanced Longitudinal Confinement in an On-Chip Atom Wave-Guide via Optical Lensing of the Atomic Wave-Packet*

We report on progress at the Army Research Laboratory towards implementation of a compact and sensitive chip-based cold atom interferometer. The interferometer makes use of $^{87}$Rb atoms magnetically confined in a wave-guide near the surface of a lithographically patterned chip. Optical lensing effects in cold atom clouds have been recently demonstrated in free space for both a single Gaussian beam [1] and a moving optical lattice potential [2]. We will discuss a similar focusing and collimation of the atomic wave-packet in the chip wave-guide. This reverses the wave-packet broadening in the longitudinal direction of the wave-guide, and therefore improved contrast in interference fringes and signal-to-noise ratio can be expected. \\[4pt] [1] Zhou et al, Phys. Rev. A \textbf{80 }033411 (2009) \\[0pt] [2] Fallani et al, Phys. Rev. Lett. \textbf{91} 240405 (2003)