Calculation of the even-odd energy difference in superfluid Fermi systems using the pseudopotential theory

The pseudopotential theory is extended to the Bogoliubov-de Gennes equations to determine the excess energy when one atom is added to the trapped superfluid Fermi system with even number of atoms. Particular attention is paid to systems being at the Feshbach resonance point. The results for relatively small particle numbers are in harmony with the Monte Carlo calculations, but are also relevant for systems with larger particle numbers. Concerning the additional one-quasiparticle state we define and determine two new universal numbers to characterize its widths.