  The complexity of the quantum state of a multiparticle system and the maximum
possible accuracy of its quantum description are connected by a relation
similar to the coordinate-momentum uncertainty relation. The coefficient in
this relation is equal to the maximum number of qubits whose dynamics can be
adequately described by quantum theory, and therefore it can be determined
experimentally through Grover search algorithm. Such a restriction of the
Copenhagen formalism is relevant for complex systems; it gives a natural
description of unitary dynamics together with decoherence and measurement, but
also implies the existence of a minimum non-zero amplitude size, as well as a
restriction on the equality of bases in the state space. The quantization of
the amplitude allows us to formally introduce a certain kind of determinism
into quantum evolution, which is important for complex systems.
