A two qubit system can be written as a superposition of possible computational basis qubit states: | 00 ⟩ ⟩ , | 01 ⟩ ⟩ , | 10 ⟩ ⟩ , | 11 ⟩ ⟩ , each with an associated complex coefficient α α : | ψ ψ ⟩ ⟩ = α α 00 | 00 ⟩ ⟩ + α α 01 | 01 ⟩ ⟩ + α α 10 | 10 ⟩ ⟩ + α α 11 | 11 ⟩ ⟩