  A quantum computer is a hypothetical device in which the laws of quantum
mechanics are used to introduce a degree of parallelism into computations and
which could therefore significantly improve on the computational speed of a
classical computer at certain tasks. Cluster state quantum computing (recently
proposed by Raussendorf and Briegel) is a new paradigm in quantum information
processing and is a departure from the conventional model of quantum
computation. The cluster state quantum computer begins by creating a highly
entangled multi-particle state (the cluster state) which it uses as a quantum
resource during the computation. Information is processed in the computer via
selected measurements on individual qubits that form the cluster state. We
describe in detail how a scalable quantum computer can be constructed using
microwave cavity QED and, in a departure from the traditional understanding of
a computer as a fixed array of computational elements, we show that cluster
state quantum computing is well suited to atomic beam experiments. We show that
all of the necessary elements have been individually realised, and that the
construction of a truly scalable atomic beam quantum computer may be an
experimental reality in the near future.
