Pseudothreshold or threshold? - More realistic threshold estimates for fault-tolerant quantum computing
Krysta M. Svore, Andrew W. Cross, Isaac L. Chuang, Alfred V. Aho · arXiv (Cornell University) · 2005
An arbitrarily reliable quantum computer can be efficiently constructed from noisy components using a recursive simulation procedure, provided that those components fail with probability less than the fault-tolerance threshold. Recent estimates of the threshold are near some experimentally achieved gate fidelities. However, the landscape of threshold estimates includes pseudothresholds, threshold estimates based on a single component and a single application of the recursive procedure. In this paper, we define pseudothresholds and present classical and quantum fault-tolerant circuits exhibiting pseudothresholds that differ significantly from fault-tolerance thresholds. Pseudothresholds are a generic phenomenon in fault-tolerant computation and recent quantum threshold estimates may in fact be pseudothresholds. We develop tools for visualizing the distinction between pseudothresholds and fault-tolerance threshold. Finally, we conjecture that refinements of these methods may establish upper bounds on the fault-tolerance threshold.