  Quantum mechanics cements the intimate relationship between the nature of
light and its detection. Historically, quantum theories of photodetection have
generally fallen into two categories: the first tries to determine what quantum
field observable is measured when photoelectrons are detected, laying the
theoretical groundwork for photodetection being possible. The second type are
phenomenological theories, which take great care to model the details of
specific photodetectors. In this dissertation, we fill in the gap between these
two models in the modern literature on photodetection by constructing a fully
quantum mechanical and sufficiently realistic model that includes all stages of
the photodetection process: transmission, amplification, and a final classical
measurement. We accomplish this within the framework of quantum information
theory using the language of positive operator valued measures (POVMs).
  This dissertation contains material previously published in three papers:
  Propp, Tz. B & van Enk, S. J. (2019). On nonlinear amplification: improved
quantum limits for photon counting. Optics Express 27, 16, 23454-23463.
  Propp, Tz. B & van Enk, S. J. (2019). Quantum networks for single photon
detection. Physical Review A, 100, 033836.
  Propp, Tz. B & van Enk, S. J. (2020). How to project onto an arbitrary
single-photon wavepacket. Physical Review A, 102, 053707.
