  The quantum adiabatic theorem ensures that a slowly changing system,
initially prepared in its ground state, will evolve to its final ground state
with arbitrary precision. As a first result this thesis extends the original
theorem to projection operators keeping the statement valid for Hamiltonians
with degenerate ground spaces.
  Yet the main focus of this work lies in studying the efficiency of quantum
circuit simulations by adabatic quantum computation. The standard Hamiltonian
construction by Kitaev is based on a path graph reflecting the $L$ computation
steps and influencing the scaling of the necessary evolution time by its
spectral gap of $\mathcal{O}\left(\frac{1}{L^2}\right)$. Aspiring to an
improved running time we generalize Kitaev's Hamiltonian to so-called standard
graph Hamiltonians based on graph families with a different spectral gap.
  In this generalized construction the first two time derivatives of the
Hamiltonian and the fraction of initial vertices appear as additional
parameters of running time. In a first step the time derivatives can be proven
to be constant. Expansion results from spectral graph theory however impose a
trade-off between the spectral gap and the fraction of initial vertices as well
as the fraction of final vertices which corresponds to the probability for
obtaining the correct computational output. Graphs with spectral gap
$\mathcal{O}\left(\frac{1}{L^k}\right)$, $k<2$, turn out to contradict very
likely, graphs with $k<1$ even for sure at least one of the efficiency
criterias for running time, output probability or Hamiltonian implementation.
  The above results may also be obstacles for a possible quantum PCP-theorem in
complexity theory claiming the local Hamiltonian problem with constant gap to
be QMA-complete since the very same Kitaev Hamiltonian is constructed in the
QMA-hardness proof for the Local Hamiltonian problem.
