  Due to the weakness of gravitational coupling, all quantum experiments up to
date in which gravity plays a role utilized the field of the Earth. Since this
field undergoes practically undetectable back-action from quantum particles, it
effectively admits a classical description as a fixed background Newtonian
field or spacetime. This argument strongly motivates theoretical and
experimental research towards a demonstration of gravitation between two
quantum masses, as this is one of the most straightforward scenarios where
quantum features of gravity could be observed. Several proposals studied the
possibility of generating entanglement between two massive objects. Along the
same lines, with a particular focus on gravity, this thesis introduces general
tools to tackle interaction-mediated entanglement and applies them to two
particles prepared in continuous-variable states.
