The quantum cat is a state of light proposed by Schrödinger: photons behave like a spinning coin, seen as both heads and tails at once. Physicists have created such a 'coin' from 120 photons, racing at the speed of light in a light trap. Usually, a large system quickly collapses into one option due to increasing disorder (entropy).

The solution proved elegant: a quantum switch (qubit) was coupled with the light and a mathematical trick was applied that naturally maintains balance. Even with noise, accuracy exceeded 96%, and without noise the method is flawless. Astonishingly, the previous record of 40 photons has been tripled. Such large cats will help probe the boundary between quantum wonders and the familiar world, and also serve as ultra-sensitive sensors and the basis for fault-tolerant quantum computers, building on the work of von Neumann. The assessment of duality comes from a special technique invented by Wigner.