On Qubits and Quantum Information Technologies

Abstract

The basic assumption underlying various quantum information technologies, such as quantum computation and quantum communication, is that qubits are physical objects. However, this assumption is false. A qubit is a quantum superposition, which is a purely mathematical entity in a Hilbert space for description of a two-level quantum system. There is no theoretical or experimental evidence for quantum superpositions in general, and for qubits in particular, having physical counterparts in the real world, although quantum systems themselves are all physical objects. Nevertheless, quantum superpositions failing to be physical objects does not necessarily imply quantum mechanics failing to be correct. Hilbert spaces differ essentially from the three-dimensional Euclidean space; the latter is the model of space in which we live and measure physical quantities. Associated with time or space coordinates, measurements of all quantum systems must be performed in the real world. However, precise time and space coordinates are not attainable by measurement. Based on a comparison between the Euclidean space and Hilbert spaces, this paper shows that no quantum systems in the real world can realize qubits, and hence, quantum information technologies are not physically realizable; their so-called advantages over classical information technologies make little sense.