cirq.operation_to_choi

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Returns the unique Choi matrix associated with an operation.

cirq.operation_to_choi(
    operation: protocols.SupportsKraus
) -> np.ndarray

Choi matrix J(E) of a linear map E: L(H1) -> L(H2) which takes linear operators on Hilbert space H1 to linear operators on Hilbert space H2 is defined as

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

where \(|\phi\rangle = \sum_i|i\rangle|i\rangle\) is the unnormalized maximally entangled state and I: L(H1) -> L(H1) is the identity map. Note that J(E) is a square matrix with d1*d2 rows and columns where d1 = dim H1 and d2 = dim H2.