Function process_fidelity 

pub fn process_fidelity(
    channel: &QuantumChannel,
    target: &QuantumChannel,
) -> Result<f64, QuantumInfoError>

Calculate the process fidelity between a quantum channel and a target.

F_pro(E, F) = F(ρ_E, ρ_F) where ρ_E = Λ_E / d is the normalized Choi matrix.

For unitary target U: F_pro(E, U) = Tr[S_U† S_E] / d²

Arguments

• channel - Quantum channel (Choi matrix or Kraus operators)
• target - Target channel or unitary

Returns

The process fidelity F_pro ∈ [0, 1]