Information and correlations in a quantum system are closely related through
the process of measurement. We explore such relation in a many-body quantum
setting, effectively bridging between quantum metrology and condensed matter
physics. To this aim we adopt the information-theory view of correlations, and
study the amount of correlations after certain classes of
Positive-Operator-Valued Measurements are locally performed. As many-body
system we consider a one-dimensional array of interacting two-level systems (a
spin chain) at zero temperature, where quantum effects are most pronounced. We
demonstrate how the optimal strategy to extract the correlations depends on the
quantum phase through a subtle interplay between local interactions and
coherence.Comment: 5 pages, 5 figures + supplementary material. To be published in PR