  A multi-branch quantum circuit is considered from the viewpoint of coherent
electron or wave transport. Starting with the closed system, we give analytical
conditions for the appearance of two isolated localized states out of the
energy band. In the open system, using the method of the effective
non-Hermitian Hamiltonian, we study signal transmission through such a circuit.
The super-radiant transition occurs when the average level width becomes
comparable to the mean level spacing. We consider also the case with on-site
disorder and find an analytical estimate, confirmed by numerical data, for the
robustness of the isolated states and their role in transport processes.
