Best,

-joe

Title: Reconstructing quantum states from single-party information

Abstract: The possible compatibility of density matrices for
single-party subsystems is described by linear constraints on their
respective spectra. Whenever some of those quantum marginal
constraints are saturated, the total quantum state has a specific,
simplified structure. We prove that these remarkable global
implications of extremal local information are stable, i.e. they hold
approximately for spectra close to the boundary of the allowed region.
Application of this general result to fermionic quantum systems allows
us to characterize natural extensions of the Hartree-Fock ansatz and
to quantify their accuracy by resorting to one-particle information,
only: The fraction of the correlation energy not recovered by such an
ansatz can be estimated from above by a simple geometric quantity in
the occupation number picture.