This short “featured article” with the schema of a programmable quantum network as a QCA (quantum cellular automaton) is used in the header of home page for “Quantum Bot” site of Alexander Vlasov.
Quantum circuits with conventional qubits are represented by complex vector spaces with Hermitian scalar product. Alternative models with real vector spaces and Euclidean scalar product also may be considered. A reduced example of such Euclidean qubit with 2D real space is also known as rebit. An extended model with 4D-real vector space is also useful, because the space corresponds to 2D complex vector space of conventional qubit.