Compute ground energy and state at a specified particle number.

Assumes the Jordan-Wigner transform. The input operator should be Hermitian and particle-number-conserving.

sparse_operator(sparse): A Jordan-Wigner encoded sparse matrix. particle_number(int): The particle number at which to compute the ground energy and states

ground_energy(float): The lowest eigenvalue of sparse_operator within the eigenspace of the number operator corresponding to particle_number. ground_state(ndarray): The ground state at the particle number