Interferometry is a universal, precision metrology tool. Matter wave interferometers have been developed over the last decades and are now used as gravimeters for prospecting and geoscience and in fundamental studies, i.e. of quantum coherence, gravitational constant measurements and dielectric response. Research is ongoing for use as accelerometers for long distance, under-water navigation and for dark matter and gravitational field exploration in space. Monolithic interferometers, where diffraction slabs are cut into a single crystal, are particularly attractive in the latter contexts due to their unsurpassed thermal and mechanical stability. However, up till now no monolithic interferometers for atoms have been realised, because atoms cannot penetrate the diffraction slabs. This project presents a completely new idea: A reflective monolithic atom interferometer with reflective slabs cut into a silicon monolith. Two configurations are considered: i) Surface Diffraction: Scattering at the intermolecular potential of Si(111)-H(1x1) (can be used with light atom beams only) and ii) Quantum diffraction: scattering at the dispersion potential from a blazed grating (can be used with all atom beams). The aim of this project is to provide a theoretical model of the new interferometer based on realistic experimental conditions and use the model to evaluate the new instrument for dark matter/gravitational waves exploration, prospecting and navigation applications. The project connects interdisciplinary expertise - the applicant Dr. Fiedler, expert on the theoretical description of matter-wave optical devices, Prof. Holst, expert on matter wave instrumentation, machine learning expert, Ass. Prof. Parviainen and theoretical particle physicist Prof. Kersten. The applicant will learn machine learning techniques, while improving several transferable skills, including scientific and grant application writing, open data and research management and science communication skills.