Returns entanglement fidelity of a given quantum channel.

Entanglement fidelity $F_e$ of a quantum channel $E: L(H) \to L(H)$ is the overlap between the maximally entangled state $|\phi\rangle = \frac{1}{\sqrt{dim H} } \sum_i|i\rangle|i\rangle$ and the state obtained by sending one half of $|\phi\rangle$ through the channel $E$, i.e.

$$ F_e = \langle\phi|(E \otimes I)(|\phi\rangle\langle\phi|)|\phi\rangle $$

where $I: L(H) \to L(H)$ is the identity map.

operation Quantum channel whose entanglement fidelity is to be computed.

Entanglement fidelity of the channel represented by operation.