  In this thesis we focus on the influence of uniform acceleration on quantum
states and their properties, as well as on quantum entanglement contained in
the vacuum. First, we analyze a quantum clock measuring time in terms of the
decay of an unstable particle. We compare the rate of ticking of a stationary
clock to the one of a uniformly accelerating clock. We discover that there
exists a deviation from what the discrepancy between those rates is predicted
to be by special relativity. In a further part of this thesis we focus on the
family of two-mode Gaussian states of two localized modes of a given quantum
field. A general framework is developed for investigating the properties of
such states, when observed by two uniformly accelerated observers, having
access to another pair of localized modes. In particular, we focus on the
vacuum state and examine the amount of quantum entanglement perceived by the
observers. The framework is developed for three cases: the quantum scalar field
in 1+1 and 3+1 dimensions and the Dirac spinor field in 1+1 dimensions. We find
that in general more entanglement is seen when the accelerations of the
observers increase and when the size of the modes of the observers and their
central frequencies decrease. Furthermore, we extend our attention also to
tripartite entanglement and investigate its extraction from the quantum vacuum
by three particle detectors in a cavity, interacting with a quantum field for a
finite time. Detailed maps of amounts of tripartite and bipartite entanglement
extracted by the detectors, are produced and compared between two types of
boundary conditions. It is found vacuum entanglement is most easily extracted
in the case of periodic boundary conditions and it is easier to extract
tripartite than bipartite entanglement.
