Thirty Years of Quantum Computing

The possibility of building a quantum computer is critically analyzed. The main point is that the general state of the hypothetical quantum computer with N qubits is characterized by 2 N quantum amplitudes, which are complex numbers restricted by the normalization condition only. It looks highly improbable that it will ever be possible to keep under our control this number of complex parameters even for modest values of [Formula: see text] 50 or 100.