Balls, strings and little elephants: Particles or Waves?

Molecular interferometry allows us to explore interesting questions on the foundations of physics and it opens new window to molecule metrology. Our experiments in Vienna started with fullerene diffraction several years ago and now allow us to play with an increasing number of different particles, with an even higher level of complexity, more and different degrees of freedom: including balls, strings and ‘little elephants’. Such experiments are intriguing and challenging since large molecules differ so strongly one from another that a multitude of different methods is required to address the diverse physical aspects and molecular properties. This includes the adaptation of molecular beams sources and detection schemes as well as methods for the preparation of coherence and the investigation of rich decoherence physics. Molecule interferometry can also serve as a new sensing tool for molecular properties, since it is highly sensitive to tiniest perturbations and beam displacements. We shall finally discuss the potential practical or fundamental limits of matter wave interferometry with large things in the future.