Using the macroscopic example of a cat, Schrödinger described what would be the normal case in the realm of the microcosm if the usual interpretation of quantum theory, especially by Niels Bohr, Werner Heisenberg and Wolfgang Paul, were correct. Accordingly, a cat that is exposed to a deadly quantum effect in a box would have to enter a ghostly superposition state: a superposition of “still alive” or “already dead” – at least until the box is opened to see what happened (BDW 9/2024, “Schrödinger’s ghostly cat”). This quantum mechanical “both-and” deeply contradicts the classic “either-or” of the everyday world.
Such apparently mutually exclusive “cat conditions” have now been proven experimentally on many occasions – although not in cats. But with the help of interferometers, even in the double-slit experiments commonly used in school lessons, waves such as particles can be caused to interfere or superpose, i.e. to be superimposed. They are then delocalized to a certain extent, i.e. spatially smeared, if they are not measured in the interferometer itself. This seems no less bizarre than a cat that is both alive and dead, because a body shouldn’t be “here” and “there” at the same time. But this may actually be the case, and to a significant extent.
More mass than an antibody
A team led by Markus Arndt, Stefan Gerlich and Sebastian Pedalino at the University of Vienna has now actually demonstrated the seemingly crazy quantum state with a sophisticated experiment. At the same time, the physicists set a new quantum record: They showed that even massive metal lumps made up of thousands of atoms can interfere and delocalize over considerable distances – in line with the predictions of quantum theory.
The new measurements are even more impressive than previous experiments. In these, individual atoms were smeared up to a distance of 50 centimeters, or for almost a quarter of an hour; A resonator weighing 0.016 grams could also be brought into superposition. Such numbers prove that quantum effects do not have to be tiny, i.e. they are limited to the microcosm, which is not accessible to our direct perception. They can become macroscopic under appropriate conditions.
This was first demonstrated in the 1980s using superconducting electrical circuits and extremely sensitive magnetic field sensors. In a sense, these are quantum systems that you can take into your hands. For such experiments, John Clarke, Michel H. Devoret and John M. Martinis from the University of California at Berkeley and Santa Barbara received the Nobel Prize in Physics in 2025.