According to Quantum mechanics, light has the property of wave-particle duality. We cannot know whether it is wave or particle until we measure it. Before we take the observation, it is said that the light is in the superposition state of wave and particle.

In Quantum Computing (QC), a qubit also has the quantum superposition nature. Linear algebra will be used to represent all these quantum natures.

The superposition of the state |1> and |0> is the linear combination 1/sqrt(2)|1> + 1/sqrt(2)|0> . And the Born’s rule states that the modulus square of the amplitude of a state ,(which is the coefficient of the basis state |1> and |0>), is the probability of that state resulting after measurement. In this case, the amplitude of |1> and |0> is 1/sqrt(2), so the probability getting 1 or 0 in measuring the qubit is 1/sqrt(2)² = 1/2.

In contrast to the classical computing, where a bit can either be 1 or 0, and is deterministic, Qubit state is probabilistic, and later we will see Quantum Computing algorithm makes use of the superposition state to achieve the performance breakthrough.