  Quantum walks underlie an important class of quantum computing algorithms,
and represent promising approaches in various simulations and practical
applications. Here we design stroboscopically monitored quantum walks and their
subsequent graphs that can naturally boost target searches. We show how to
construct walks with the property that all the eigenvalues of the non-Hermitian
survival operator, describing the mixed effects of unitary dynamics and the
back-action of measurement, coalesce to zero, corresponding to an exceptional
point whose degree is the size of the system. Generally, the resulting search
is guaranteed to succeed in a bounded time for any initial condition, which is
faster than classical random walks or quantum walks on typical graphs. We then
show how this efficient quantum search is related to a quantized topological
winding number and further discuss the connection of the problem to an
effective massless Dirac particle.
