Transition to the Macroscopic World

Detlef Dürr, Stefan Teufel

Andrea López-Incera, Wolfgang Dür, Stefan Heusler

Abstract Schrödinger’s cat is an iconic example for the problem of the transition from the microscopic quantum world to the macroscopic, classical one. Up to which system size quantum effects can be expected? How can the transition between the classical and the quantum world be characterized? The field of macroscopicity aims at providing answers to those questions, both from a theoretical and an experimental point of view. Here, we present the main concepts in macroscopicity, including macroscopicity measures, experimental realizations and the link to metrology, from a pedagogical perspective. We provide visualizations and intuitive explanations, together with a hands-on activity where students can create their own macroscopic quantum cats from cardboard cells that are in a superposition of being dead and alive.

Gordon Baym, Eduardo Fradkin

Tony Leggett (1938-2026) was one of the great theoretical physicists of his generation, specializing in the quantum mechanics of fluids and solids. Rightly recognized by the 2003 Nobel Prize in Physics for his explanation of the experiments discovering the superfluidity of helium-3, he will be remembered equally for his pioneering inquiries into the transition from the quantum to the classical world and the extent to which we can observe quantum phenomena on macroscopic scales.

Inge Svein Helland

Marco Genovese

We present a panoramic view on various attempts to "solve" the problems of quantum measurement and macro-objectivation, i.e. of the transition from a probabilistic quantum mechanic microscopic world to a deterministic classical macroscopic world.

Inge Svein Helland