Recently, it was realized that use of the properties of quantum mechanics
might speed up certain computations dramatically. Interest in quantum
computation has since been growing. One of the main difficulties of realizing
quantum computation is that decoherence tends to destroy the information in a
superposition of states in a quantum computer, thus making long computations
impossible. A futher difficulty is that inaccuracies in quantum state
transformations throughout the computation accumulate, rendering the output of
long computations unreliable. It was previously known that a quantum circuit
with t gates could tolerate O(1/t) amounts of inaccuracy and decoherence per
gate. We show, for any quantum computation with t gates, how to build a
polynomial size quantum circuit that can tolerate O(1/(log t)^c) amounts of
inaccuracy and decoherence per gate, for some constant c. We do this by showing
how to compute using quantum error correcting codes. These codes were
previously known to provide resistance to errors while storing and transmitting
quantum data.Comment: Latex, 11 pages, no figures, in 37th Symposium on Foundations of
Computing, IEEE Computer Society Press, 1996, pp. 56-6
