Measurement-induced quantum-to-classical transition in a chaotic gravitational wedge

Quantum mechanics is the most fundamental theory describing nature, and according to the correspondence principle, classical mechanics should emerge from it. However, in areas like chaotic motion, the connection between classical and quantum descriptions is not straightforward. A key challenge is understanding how classical chaotic behaviour, especially sensitivity to initial conditions, arises from quantum mechanics. Measurement processes are expected to drive such transitions, yet they raise many unresolved questions, known collectively as the measurement problem—including whether wavefunction collapse is a real physical process. Here, we experimentally study the quantum-to-classical transition in a two-dimensional billiard system. Position-dependent gain in this system acts similarly to a measurement, reducing quantum superpositions to eigenstates. By varying the gain position, we observe sensitivity to initial conditions via mode jumps. Our experiment offers a concrete example of how measurement-like processes can yield classical chaotic behaviour in a quantum system. Unlike idealized axiomatic measurements, our process is a tangible physical phenomenon, offering new insight into the nature of quantum measurements.