The quantum state of any state is not directly observable.

For a qubit in the state , when we measure this qubit in the computational basis, it gives outcome 0 with probability and outcome 1 with probability .

Note that after we measure a state in the computational basis, it is no longer in the superposition state. Instead, if we get outcome 0, the quantum state will be . And same for 1.

The following circuit denoting measurements in the quantum circuit model. Note that we use the double wire at right to indicate that the measurement outputs a classical bit (either 0 or 1).