This node calculate the fidelity $F = |\langle \psi | \varphi \rangle |^2$ between two states. It is the norm-squared of the overlap of any two states $\psi$ and $\varphi$.
The node has the following inputs:
It displays the norm-square of the overlap between the states $\psi$ and $\varphi$ provided as inputs.
In the example below, the fidelity between a stationary state and a non-stationary (linear combination of the first two eigenstates) state is calculated by the Fidelity node.