Quantal ‘Tapes’

Abstract

So far we have considered observables represented by a single quantal ‘bit’, or a pair of qubits. These could be of hermitean type, as in Sects. 2.1 and 2.2, or of pseudo-hermitean type, as in the last two sections. In quantal information processing, and in quantized field theory, the matrix representation of a ‘tape’, consisting of several or even many qubits of the same type, is required. This can be constructed by direct multiplication from the representations of the separate qubits, which may be but are not necessarily of the same type. The simplest example, where no more than two qubits were involved, was considered in Sect. 3.4.