The process of observing the state of a quantum system is known as measurement. Measuring a quantum system generally changes the quantum state that describes that system. The act of measurement will project the quantum state onto one of the eigenvectors of the Hilbert space that represents the system. When your system is a qubit, it will collapse from a value anywhere on the Bloch Sphere to either a 0 or 1 (the “north” or “south” pole of the Bloch Sphere; this is called Z-basis measurement). Measurement is one of the key features that distinguishes quantum mechanics from classical mechanics: if one measures a quantum state, the full quantum information is lost and the quantum state changes. This is sometimes referred to as the “measurement problem”.