Natural orbits of atomic Cooper pairs in a nonuniform Fermi gas

We present the natural orbits of atomic Cooper pairs in an inhomogeneous Fermi gas. These orbits provide the pairing mode functions of constructing BCS states in finite systems. We further exploit such orbits to study Cooper pair wave functions in various trapping situations. In particular, we quantify and characterize the quantum entanglement between atoms in a Cooper pair associated with the spatial degrees of freedom. \newline (Reference : Y.H. Pong, C.K. Law, Phy. Rev. A \textbf{74}, 013618 (2006))