The effects of radiative cascades on the x-ray diagnostic lines of Fe¹⁶⁺

Abstract

We demonstrate, in an elementary manner, that given a partition of the single\nparticle Hilbert space into orthogonal subspaces, a Fermi sea may be factored\ninto pairs of entangled modes, similar to a BCS state. We derive expressions\nfor the entropy and for the particle number fluctuations of a subspace of a\nfermi sea, at zero and finite temperatures, and relate these by a lower bound\non the entropy. As an application we investigate analytically and numerically\nthese quantities for electrons in the lowest Landau level of a quantum Hall\nsample.\n