Closed loop examples

The specific properties of closed loop eigenfunctions deserve to be better understood. This chapter underlines that responses in closed loops differ from the responses in open loops. Within the following simple examples, constructed on closed loop robust zeros, many path states are found. A robust eigenfunction zero is robust because its eigenstate cannot be activated by any action applied on it. The path states are robust because they are confined within one-dimensional paths, and when they are degenerate they can turn around defects.