  This thesis is a compilation of research in relativistic quantum information
theory, and research in quantum reference frames. The research in the former
category provides a fundamental construction of quantum information theory of
localised qubits in curved spacetimes. For example, this concerns quantum
experiments on free-space photons and electrons in the vicinity of the Earth.
From field theory a description of localised qubits that traverse classical
trajectories in curved spacetimes is obtained, for photons and massive spin-1/2
fermions. The equations governing the evolution of the two-dimensional quantum
state and its absolute phase are determined. Quantum information theory of
these qubits is then developed. The Stern-Gerlach measurement formalism for
massive spin-1/2 fermions is also derived from field theory. In the latter
category of research, the process of changing reference frames is considered
for the case where the reference frames are quantum systems. As part of this
process, it is shown that decoherence is necessarily induced on any quantum
system described relative to these frames. This process is explored using
examples involving quantum reference frames for phase and orientation.
Quantifying the effect of changing quantum reference frames provides a
theoretical description for this process in quantum experiments, and serves as
a first step in developing a relativity principle for theories in which all
objects including reference frames are necessarily quantum.
