Compact Atom Sources for Optical Frequency Standards

Abstract

Atomic clocks are crucial for precise time dissemination, supporting industrial applications for navigation, telecommunication, the financial system, and the energy industry by ensuring accurate timekeeping and synchronization. At present, the best atomic clocks are based on optical transitions. Optical lattice clocks based on Yb or Sr achieve fractional frequency uncertainties in the low 10^−18 regime. This remarkable accuracy allows resolving the gravitational redshift on the centimeter scale. This progress has driven the development of compact transportable optical lattice clocks, which are crucial for field- or even space applications. Especially for space operation, there is a critical need to minimize size, weight and power consumption of key components, particularly the source of laser-cooled atoms. Conventional atom sources for optical lattice clocks consist of an atomic oven with a high power consumption and a six-beam magneto-optical trap (MOT) that requires a large and complex optical setup. This thesis addresses the technical challenges associated with the development of compact sources of laser-cooled alkaline-earth-like atoms by demonstrating a miniaturized atomic oven and a miniaturized MOT for Yb and Sr. The MOT generation is tested with three types of in-vacuum optical elements that generate all the required laser beams for three-dimensional trapping and cooling with only one single input beam. A quasi-monolithic aluminum structure generating a conventional MOT beam geometry that is called pyramid reflector is compared to a quasi-planar optical element called Fresnel reflector. Both are characterized and compared using the same high-flux Yb source. Particularly, two-stage cooling of a fermionic alkaline-earth-like atom in a non-conventional MOT configuration is performed for the first time, demonstrating the applicability of planar MOT optics in optical lattice clocks. Furthermore, a planar diffraction grating is combined with the miniaturized atomic oven inside a highly compact vacuum chamber. The atomic oven is based on a circular fused silica chip and is tested by loading an Yb MOT generated with the pyramid reflector and a Sr MOT generated with the diffraction grating. It requires less than 250 mW of electrical heating power to generate a MOT loading rate above 10^8 atoms/s with the pyramid reflector. The presented components form a compact source of laser-cooled Yb or Sr atoms, and, when combined with a compact optical lattice setup, will serve as the basic building blocks of a future transportable optical lattice clock.