Compute an eigenvalue and eigenstate of a quadratic Hamiltonian.

Eigenstates of a quadratic Hamiltonian are also known as fermionic Gaussian states.

quadratic_hamiltonian(QuadraticHamiltonian): The Hamiltonian whose eigenstate is desired. occupied_orbitals(list): A list of integers representing the indices of the occupied orbitals in the desired Gaussian state. If this is None (the default), then it is assumed that the ground state is desired, i.e., the orbitals with negative energies are filled.


energy (float):
    The eigenvalue.
state (sparse):
    The eigenstate in scipy.sparse csc format.