  In this thesis, we study aspects of entanglement theory of quantum field
theories from an algebraic point of view. The main motivation is to gain
insights about the general structure of the entanglement in QFT, towards a
definition of an entropic version of QFT. In the opposite direction, we are
also interested in exploring any consequence of the entanglement in algebraic
QFT. This may help us to reveal unknown features of QFT, with the final aim of
finding a dynamical principle which allows us to construct non-trivial and
rigorous models of QFT. The algebraic approach is the natural framework to
define and study entanglement in QFT, and hence, to pose the above inquiries.
After a self-contained review of algebraic QFT and quantum information theory
in operator algebras, we focus on our results. We compute, in a mathematically
rigorous way, exact solutions of entanglement measures and modular Hamiltonians
for specific QFT models, using algebraic tools from modular theory of von
Neumann algebras. These calculations show explicitly non-local features of
modular Hamiltonians and help us to solve ambiguities that arise in other
non-rigorous computations. We also study aspects of entanglement entropy in
theories having superselection sectors coming from global symmetries. We follow
the algebraic perspective of Doplicher, Haag, and Roberts. In this way, we find
an entropic order parameter that "measures" the size of the symmetry group,
which is made out of a difference of two mutual informations. Moreover, we
identify the main operators that take account of such a difference, and we
obtain a new quantum information quantity, the entropic certainty relation,
involving algebras containing such operators. This certainty relation keeps an
intrinsic connection with subfactor theory of von Neumann algebras.
