  We present a scheme for linear optical quantum computation (LOQC) which is
highly robust to imperfect single photon sources and inefficient detectors. In
particular we show that if the product of the detector efficiency with the
source efficiency is greater than 2/3, then efficient LOQC is possible. This
threshold is many orders of magnitude more relaxed than those which could be
inferred by application of standard results in fault tolerance. The result is
achieved within the cluster state paradigm for quantum computation.
