In quantum mechanics, when a measurement is performed on a quantum system, such as an atom, the change in the system's state or position is described by the process known as wavefunction collapse or wavefunction reduction.
The state of a quantum system is typically described by its wavefunction, which contains information about the probabilities of various outcomes of a measurement. Before the measurement, the wavefunction of the system is in a superposition, meaning it represents a combination of different possible states. However, when a measurement is made, the wavefunction "collapses" into one of the possible states corresponding to the measurement outcome. This collapse is a non-deterministic process, and the specific outcome is chosen randomly according to the probabilities encoded in the wavefunction.
The collapse of the wavefunction is often associated with an interaction between the quantum system and the measurement apparatus or the external environment. This interaction causes the entanglement between the system and the measuring device, leading to the collapse of the system's wavefunction into a definite state.
After the collapse, the state of the system is determined by the measurement outcome, and its position will be associated with the particular outcome that was observed. The precise details of how this collapse occurs and the exact mechanism behind it are still the subject of debate and interpretation in quantum mechanics, with different interpretations proposing various mechanisms or explanations for the collapse process.
It's important to note that the collapse of the wavefunction is a fundamental aspect of quantum mechanics, and it distinguishes it from classical physics. In classical physics, the act of measurement does not cause a fundamental change in the state of a system but merely reveals pre-existing properties. In quantum mechanics, however, the act of measurement fundamentally alters the state of the system being measured.