In quantum mechanics, wavefunction collapse (WFC) occurs when a wavefunction, initially composed of a weighted superposition of several eigenstates, reduces to a single eigenstate. The probability of collapse into any eigenstate is commensurate with its (squared) amplitude in the original superposition. In QM, collapse happens upon any attempt to observe/measure the wavefunction. "Wavefunction collapse" also refers more generally to symmetry-breaking processes that are functionally analogous to WFC in quantum mechanics, such as sampling tokens in autoregressive generation.