In quantum mechanics, the collapse of a particle's wave function occurs when a measurement is made on the particle. This collapse represents the transition from a superposition of possible states to a definite state as a result of the measurement. Once the wave function collapses, the particle is described by a specific state or eigenstate corresponding to the measured value.
After the collapse, the particle remains in a definite state unless another interaction or measurement occurs. In this sense, it does not spontaneously regain its wave function or revert back to a superposition of states. The subsequent behavior of the particle will be governed by the new state it has collapsed into.
However, it's important to note that the time evolution of the particle's wave function is determined by the Schrödinger equation, which describes how the wave function changes over time. Under specific conditions and interactions, such as in free space or certain potential fields, the wave function can spread out and exhibit wave-like behavior over time. This is known as wave packet dispersion.
But it's crucial to understand that the collapse of the wave function is a fundamental aspect of the measurement process in quantum mechanics, and once collapsed, the particle is described by a definite state. The subsequent evolution of the particle's wave function will depend on its interactions and the physical conditions it experiences.