Continuous theory of operator expansions of finite dimensional Hilbert spaces, continuous structures of quantum circuits and decidability

Abstract

We consider continuous structures which are obtained from finite dimensional Hilbert spaces over $\mathbb{C}$ by adding some unitary operators. Quantum automata and circuits are naturally interpretable in such structures. We consider appropriate algorithmic problems concerning continuous theories of natural classes of these structures. We connect them with the topic of approximations by metric groups. This paper extends and corrects the paper A. Ivanov, "Continuous structures of quantum circuits", arXiv: 1406.4635. Replacing version contains a new section (Section 4.4).