openfermion.transforms.get_interaction_operator

Convert a 2-body fermionic operator to InteractionOperator.

openfermion.transforms.get_interaction_operator(
    fermion_operator, n_qubits=None
)

This function should only be called on fermionic operators which consist of only a_p^\dagger a_q and a_p^\dagger a_q^\dagger a_r a_s terms. The one-body terms are stored in a matrix, one_body[p, q], and the two-body terms are stored in a tensor, two_body[p, q, r, s].

interaction_operator An instance of the InteractionOperator class.

TypeError Input must be a FermionOperator.
TypeError FermionOperator does not map to InteractionOperator.

Even assuming that each creation or annihilation operator appears at most a constant number of times in the original operator, the runtime of this method is exponential in the number of qubits.