  Over the past three decades, quantum mechanics has allowed the development of
technologies that provide unconditionally secure communication. In parallel,
the quantum nature of the transverse electromagnetic field has spawned the
field of quantum imaging that encompasses technologies such as quantum ghost
imaging and high-dimensional quantum key distribution (QKD). The emergence of
such quantum technologies also highlights the need for the development of
methods for characterizing the elusive quantum state itself. In this document,
we describe new technologies that use the quantum properties of light for
security. The first is a technique that extends the principles behind QKD to
the field of imaging. By applying the polarization-based BB84 protocol to
individual photons in an active imaging system, we obtained images that are
secure against intercept-resend jamming attacks. The second technology
presented in this article is based on an extension of quantum ghost imaging. We
used a holographic filtering technique to build a quantum ghost image
identification system that uses a few pairs of photons to identify an object
from a set of known objects. The third technology addressed in this document is
a high-dimensional QKD system that uses orbital-angular-momentum (OAM) modes of
light for encoding. Moving to a high-dimensional state space in QKD allows one
to impress more information on each photon, as well as introduce higher levels
of security. We discuss the development of two OAM-QKD protocols based on the
BB84 and Ekert QKD protocols. The fourth and final technology presented in this
article is a relatively new technique called direct measurement that uses
sequential weak and strong measurements to characterize a quantum state. We use
this technique to characterize the quantum state of a photon with a
dimensionality of d=27, and measure its rotation in the natural basis of OAM.
