78 research outputs found

    Turing machines based on unsharp quantum logic

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    In this paper, we consider Turing machines based on unsharp quantum logic. For a lattice-ordered quantum multiple-valued (MV) algebra E, we introduce E-valued non-deterministic Turing machines (ENTMs) and E-valued deterministic Turing machines (EDTMs). We discuss different E-valued recursively enumerable languages from width-first and depth-first recognition. We find that width-first recognition is equal to or less than depth-first recognition in general. The equivalence requires an underlying E value lattice to degenerate into an MV algebra. We also study variants of ENTMs. ENTMs with a classical initial state and ENTMs with a classical final state have the same power as ENTMs with quantum initial and final states. In particular, the latter can be simulated by ENTMs with classical transitions under a certain condition. Using these findings, we prove that ENTMs are not equivalent to EDTMs and that ENTMs are more powerful than EDTMs. This is a notable difference from the classical Turing machines.Comment: In Proceedings QPL 2011, arXiv:1210.029

    A true concurrency model of CCS semantics

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    AbstractDegano et al. (1989) introduced AC/E systems (augmented C/E systems) to give a true concurrency semantics to CCS. But the true concurrency was not complete. There was no true concurrency for recursive agents (like <x>.e1|e2) and nondeterminant agents (like e1|e2+e3|e4). Also the concept of bisimulation has not been transplanted to AC/E systems. This paper defines a complete true concurrency model of CCS by exploiting the potential concurrency of any CCS agent to its full strength. It introduces a kind of multilayered Petri nets, called NP/R nets, to define the processes on AC/E systems. We also introduced the notion of bisimulation of groups of NP/R nets and proved that this bisimulation relation can determine the CCS bisimulation uniquely

    New class of 3D topological insulator in double perovskite

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    We predict a new class of three-dimensional topological insulators (TIs) in which the spin-orbit coupling (SOC) can more effectively generate a large band gap at Γ\Gamma point. The band gap of conventional TI such as Bi2_2Se3_3 is mainly limited by two factors, the strength of SOC and, from electronic structure perspective, the band gap when SOC is absent. While the former is an atomic property, we find that the latter can be minimized in a generic rock-salt lattice model in which a stable crossing of bands {\it at} the Fermi level along with band character inversion occurs for a range of parameters in the absence of SOC. Thus, large-gap TI's or TI's comprised of lighter elements can be expected. In fact, we find by performing first-principle calculations that the model applies to a class of double perovskites A2_2BiXO6_6 (A = Ca, Sr, Ba; X = Br, I) and the band gap is predicted up to 0.55 eV. Besides, more detailed calculations considering realistic surface structure indicate that the Dirac cones are robust against the presence of dangling bond at the boundary with a specific termination.Comment: submitted; title changed and new references added; see DOI for published versio