AlbaNova and Nordita colloquium

Universal Matter-Wave Interferometry 

Prof. Markus Arndt (University of Vienna)

23 october 2025, 15:15 - The Oskar Klein auditorium (FR4)

Quantum mechanics is celebrating its centenary, commemorating de Broglie’s matter wave hypothesis, Heisenberg’s matrix mechanics, Schrödinger's wave equation and many other fundamental achievements.  Confirmed by countless experiments, quantum theory has since become the foundation of a vast range of technologies.  Yet, we still struggle to grasp the meaning of the quantum wave function, the interpretation of its formalism and its implications for the nature of reality. This talk will illustrate the conundrum by exploring how quantum superpositions and extended wave functions of massive objects can be prepared in states that appear forbidden from the perspective of our macroscopic everyday world.

I will discuss the experimental conditions, realizations, and applications of matter-wave interferometry which we have extended across diverse material classes and ever-increasing mass scales: from C60 molecules to vitamins and polypeptides, molecular clusters, and metal nanoparticles containing thousands of atoms in a single delocalized body. In all cases, we confirm that quantum superpositions can be realized, in stark contradiction to a classical world view that assumes massive bodies traveling along well-defined trajectories. Our experiments have grown from ‘Schrödinger kittens’ to mesoscopic cats and I will highlight the next steps on this journey.