Quantum Computers

This paper first considers sequential quantum machines (SQMs). The SQMs thatpossess an isometric transition operator and the SQMs that are factorizable orstrongly factorizable are characterized. Quantum Turing machines (QTMs) arestudied next and an alternative proof of the result that characterizes the unitaryevolution of a QTM is given. It is shown that any QTM can be represented interms of two quantum printers which are much simpler than a QTM. UnidirectionalQTMs are studied and it is shown that their corresponding quantum printers areclosely related to each other. A simple method for constructing unidirectionalQTMs is given. Finally, a preliminary development of generalized QTMs andquantum pushdown automata is presented.