Coherent manipulation of ultracold atoms an atom chips

TL;DR: In this paper, the effect of the atom chip surface on internal-state coherence was investigated and a chip-based atomic clock was demonstrated, achieving a relative frequency stability of 1.7 × 10−11 (τ [s])−1/2.

Abstract: In this thesis, I report experiments and theoretical work on the coherent manipulation of ultracold atoms on an atom chip. We experimentally investigate the effect of the atom chip surface on internal-state coherence and demonstrate a chip-based atomic clock. Theoretical proposals are made for a robust atom chip quantum gate and for the coupling of a Bose-Einstein condensate to a nanoelectromechanical system. In our experiments, we trap atoms in a magnetic microchip trap and prepare them in a coherent superposition of two internal states with nearly identical magnetic moments. By performing Ramsey interferometry we investigate the effect of atom-surface interactions on internal-state coherence. Trap and coherence lifetimes exceeding 1 s are observed with atoms at distances of 5 − 130 μm from the chip surface. The coherence lifetime in the chip trap agrees well with the results of similar measurements in macroscopic magnetic traps. At distances below 5 μm, loss of atoms occurs due to the attractive Casimir-Polder surface potential. We make use of the good coherence properties to demonstrate a chipbased atomic clock and measure its relative frequency stability to 1.7 × 10−11 (τ [s])−1/2. Our measurements show that with straightforward improvements a relative stability in the 10−13 (τ [s])−1/2 range is realistic. An atom chip clock may find applications as a portable secondary standard and in satellite navigation. We propose to use our state pair for quantum information processing and describe a realistic implementation of a collisional quantum phase gate on an atom chip. In our proposal, a key role is played by state-selective microwave near-field potentials. These potentials are a useful new tool for atom chip experiments. They combine the versatility of optical dipole traps with the dissipationless character of static magnetic potentials and the adjustable geometry of a near-field trap. We describe the design and fabrication of a multi-layer atom chip for experiments with microwave near-fields. The work reported here shows that atom chips are a versatile system for quantum engineering. Moreover, atom chips enable new and intriguing experiments at the boundary between quantum optics and condensed matter physics. As an example, we propose to couple a Bose-Einstein condensate to the mechanical oscillations of a nanoscale cantilever with a magnetic tip. This system realizes a mechanical analog of cavity quantum electrodynamics, with the possibility to reach the strong coupling regime.