  Experimental attempts to implement quantum speedup of computations over the
past 30 years have yielded a negative result, despite the absence of physical
laws prohibiting such speedup. The article formulates the limitation of quantum
formalism in the form of uncertainty "the complexity of the system - the
accuracy of its description at the quantum level", and provides arguments in
favor of its physical status. An experiment to determine this constant through
Grover's algorithm is described. Rough estimates on the constant of this ratio
are given, based on the possibility of applying the quantum theory to two
processes: the emission of a photon by a Rubidium atom and the decay of an
unstable isotope of Helium 6. This ratio explicitly prohibits the physical
implementation of scalable fast quantum computations, but leaves the
possibility of modeling the dynamics of real systems on a quantum computer, the
only advantage of which is the use of quantum nonlocality.
