Revisiting the hopes for scalable quantum computation
M. I. Dyakonov
Laboratoire Charles Coulomb, Université Montpellier II, CNRS, 34095 Montpellier, France
Abstract
The hopes for scalable quantum computing rely on the "threshold theorem": once the error
per qubit per gate is below a certain value, the methods of quantum error correction allow
indefinitely long quantum computations. The proof is based on a number of assumptions, which
are supposed to be satisfied exactly, like axioms, e.g. zero undesired interactions between qubits, etc. However, in the physical world no continuous quantity can be exactly zero,
it can only be more or less small. Thus the "error per qubit per gate" threshold must be
complemented by the required precision with which each assumption should be fulfilled. In the absence of this crucial information, the prospects of scalable quantum computing remain uncertain.