We present a method which can be used to convert certain single photon sources, such as quantum dots, into devices capable of emitting large strings of photonic cluster states in a controlled and pulsed "on demand" manner. Such sources greatly alleviate the resources required to achieve linear optical quantum computation. Standard spin errors, such as dephasing, are shown to affect only 1 or 2 of the emitted photons at a time. This allows for the use of standard fault tolerance techniques, and shows that the machine gun can be fired for arbitrarily long times. Using realistic parameters for current semiconductor quantum dot sources, we conclude high entangled-photon emission rates are achievable, with Pauli-error rates less than 0.2%.
http://arxiv.org/abs/0810.2587