Quantum foundations research aims to probe the heart of quantum theory to understand it deeply and comprehensively. Bose-Einstein condensates are well-suited to foundations experiments, as their large-scale coherence allows them to act like a single large atom rather than an ensemble of thousands, well described by a single-particle wavefunction. I will describe two experiments that we have performed using our BEC of rubidium-87 which exploit these properties. The first experiment shows how geometric phases arise between different spin states of the condensate due to off-resonant couplings. The resulting interference pattern is an example of how these kinds of phases can create disturbances when performing complex operations on quantum systems, and it may be an important consideration in many quantum computing platforms. The second experiment is a weak version of a Stern-Gerlach experiment. By weakly separating two spin components of the BEC and post-selecting on an unlikely final state, the shift created by an external magnetic gradient is amplified by a factor of 14, effectively measuring a spin of 7 for a spin-1/2 particle. This experiment is the first of its kind using atoms, and future versions may be used for detecting small magnetic moments or for magnetic gradiometry.