  We study the entanglement Hamiltonian for a spherical domain in the ground
state of a nonrelativistic free-fermion gas in arbitrary dimensions. Decomposed
into a set of radial entanglement Hamiltonians, we show that the entanglement
spectrum in each sector is identical to that of a hopping chain in a linear
potential, with the angular momentum playing the role of the subsystem
boundary. Furthermore, the eigenfunctions follow from a commuting differential
operator that has exactly the form predicted by conformal field theory.
Rescaled by the radial Fermi velocity, this operator gives a perfect
approximation of the entanglement Hamiltonian, except for large angular momenta
that belong to the edge regime in the analogous gradient chain. One thus finds
that the conformal field theory result becomes asymptotically exact only in one
dimension.
