After the measurement of a qubit, its quantum state "collapses" into one of the possible measurement outcomes. The measurement outcome corresponds to one of the eigenstates of the observable being measured. In quantum mechanics, the act of measurement causes the system to transition from a superposition of states to a definite state.
The outcome of a measurement is probabilistic, and the probabilities of different outcomes are determined by the quantum state of the qubit prior to the measurement. Specifically, the probability of obtaining a particular measurement outcome is given by the squared magnitude of the corresponding coefficient in the quantum state's superposition.
Once the measurement is performed and a specific outcome is obtained, the qubit's state is no longer in a superposition but is in a well-defined state corresponding to the measurement result. This collapse of the quantum state is often referred to as the "measurement collapse" or "wavefunction collapse." The collapse is a fundamental aspect of quantum mechanics but can be conceptually challenging as it involves a transition from probabilistic superposition to a definite state.
It's important to note that after the measurement, the subsequent behavior of the qubit will depend on the specific application or context. In some cases, the measured value may be used in further computations or information processing. In other cases, the measured qubit may interact with other qubits, leading to entanglement and more complex quantum dynamics.
Overall, the act of measurement in quantum mechanics is a process that extracts information from a quantum system and causes the collapse of its quantum state into a definite outcome, enabling the extraction of classical information from quantum systems.