  This work is concerned with phrasing the concepts of fault-tolerant quantum
computation within the framework of disordered systems, Bernoulli site
percolation in particular. We show how the so-called "threshold theorems" on
the possibility of fault-tolerant quantum computation with constant error rate
can be cast as a renormalization (coarse-graining) of the site percolation
process describing the occurrence of errors during computation. We also use
percolation techniques to derive a trade-off between the complexity overhead of
the fault-tolerant circuit and the threshold error rate.
