  The thesis establishes a link between theoretical foundations and practical
applications in the emerging field of propagating quantum microwaves. Although
the concrete focus of the main results lies in specific quantum communication
and sensing protocols, the thesis also gives a self-contained introduction to
quantum parameter estimation and Gaussian quantum continuous variables,
justifying the theoretical results used. Motivated, firstly, by the
compatibility between superconducting circuits (a promising quantum computing
platform), and the microwave frequency range; and, secondly, by the
transparency window of the atmosphere to these frequencies, the work contains
two concrete contributions to the fields of microwave quantum sensing and
communication: a novel protocol that uses frequency entanglement to measure the
first order dependence in frequency of the reflectivity of an object; and a
large investigation on different aspects of entanglement degradation due to
loss and atmospheric absorption in the context of continuous-variable
entanglement distribution for the task of quantum teleportation in open-air.
  The dissertation includes, as a last chapter, an article that reviews the
state-of-the-art in quantum microwave technology, and proposes different
research lines, including quantum communication between Earth-based stations
and satellites, quantum radar, direct dark matter detection, and exploration of
the quantum properties of the cosmic microwave background. This more
speculative, yet rigorous chapter closes with a roadmap for possible future
research lines in the field of propagating quantum microwaves, that can serve
as an outlook of the thesis.
