openfermion.transforms.get_quadratic_hamiltonian

Convert a quadratic fermionic operator to QuadraticHamiltonian.

openfermion.transforms.get_quadratic_hamiltonian(
    fermion_operator,
    chemical_potential=0.0,
    n_qubits=None,
    ignore_incompatible_terms=False
)

Used in the notebooks

Used in the tutorials

fermion_operator FermionOperator

The operator to convert.

chemical_potential float

A chemical potential to include in the returned operator

n_qubits int

Optionally specify the total number of qubits in the system

ignore_incompatible_terms bool

This flag determines the behavior of this method when it encounters terms that are not quadratic that is, terms that are not of the form a^\dagger_p a_q. If set to True, this method will simply ignore those terms. If False, then this method will raise an error if it encounters such a term. The default setting is False.

quadratic_hamiltonian An instance of the QuadraticHamiltonian class.

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

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.