Newtonian self-gravity in trapped quantum systems and experimental tests

No experimental evidence exists, to date, whether or not the gravitational field must be quantised. Theoretical arguments in favour of quantisation are inconclusive. The most straightforward alternative to quantum gravity, a coupling between classical gravity and quantum matter according to the semi-classical Einstein equations, yields a nonlinear modification of the Schr"odinger equation. Here, effects of this so-called Schr"odinger-Newton equation are discussed, which allow for technologically feasible experimental tests.