A high-flux cold atom source based on a nano-structured atom chip

Abstract

Modern physics is challenged by existential questions about the most fundamental interactions of matter. While three of the four known fundamental forces are modeled in the grand unified theory [1], gravity seems to be incompatible in its current formulation. Many physicists search to unify them, but often the invented models violate well-tested assumptions such as the Einstein Equivalence Principle, a cornerstone of General Relativity. Despite macroscopic tests of this principle have already been carried out to high precision [2–4], quantum tests exploiting matter-wave interferometry [5–7] may provide complementary information [8] with even higher precision [9–11]. These yield their ultimate performance with Bose-Einstein condensates (BECs) over long evolution times as conventionally achieved by free-fall in space [12]. As such, a new generation of high performance BEC sources is required with strict budgets on size, weight and power demands. Efforts to miniaturize these sources have been pursued with promising results using atom chips [13–15], but further miniaturization of these setups is necessary. In an attempt to simplify the usage of atom chips, the following thesis describes the development of a nano-structured atom chip that allows for single-beam magneto-optical trapping. The chip is implemented in a dedicated atom chip test facility that has been planned, built and characterized in the scope of this thesis. The facility features a state-of-the-art master oscillator power amplifier laser system, compact control electronics [13,15–17] and a high-flux 2D+-MOT as an atomic source. Despite the simplified setup, magneto-optical trapping of 1.1 × 10^9 Rubidium atoms was achieved within 1 s which is comparable to other atom chip setups and well above previous achievements with grating MOTs [18–23]. Illuminating the grating with a beam profile from a custom-built top-hat beam expander was instrumental to achieve balanced laser cooling in a large volume above the grating. This allowed to cool 4.7 × 10^8 atoms to 13 µK and transfer 2.4 × 10^8 atoms into a large-volume Ioffe-Pritchard type magnetic chip trap, demonstrating the required mode-matching between the laser cooled atoms and the magnetic trap. The trapped atoms were then used to characterize the magnetic field environment of the test facility using radio frequency spectroscopy gauging the surrounding magnetic bias coils. These results demonstrate the feasibility of using a nano structured atom chip to build a single-beam BEC source which could become the foundation of future high-performance quantum sensors on ground and in space.