7,912 research outputs found
Computational Processes and Incompleteness
We introduce a formal definition of Wolfram's notion of computational process
based on cellular automata, a physics-like model of computation. There is a
natural classification of these processes into decidable, intermediate and
complete. It is shown that in the context of standard finite injury priority
arguments one cannot establish the existence of an intermediate computational
process
Lattice Gauge Tensor Networks
We present a unified framework to describe lattice gauge theories by means of
tensor networks: this framework is efficient as it exploits the high amount of
local symmetry content native of these systems describing only the gauge
invariant subspace. Compared to a standard tensor network description, the
gauge invariant one allows to speed-up real and imaginary time evolution of a
factor that is up to the square of the dimension of the link variable. The
gauge invariant tensor network description is based on the quantum link
formulation, a compact and intuitive formulation for gauge theories on the
lattice, and it is alternative to and can be combined with the global symmetric
tensor network description. We present some paradigmatic examples that show how
this architecture might be used to describe the physics of condensed matter and
high-energy physics systems. Finally, we present a cellular automata analysis
which estimates the gauge invariant Hilbert space dimension as a function of
the number of lattice sites and that might guide the search for effective
simplified models of complex theories.Comment: 28 pages, 9 figure
Turing degrees of limit sets of cellular automata
Cellular automata are discrete dynamical systems and a model of computation.
The limit set of a cellular automaton consists of the configurations having an
infinite sequence of preimages. It is well known that these always contain a
computable point and that any non-trivial property on them is undecidable. We
go one step further in this article by giving a full characterization of the
sets of Turing degrees of cellular automata: they are the same as the sets of
Turing degrees of effectively closed sets containing a computable point
Exhaustive Generation of Linear Orthogonal Cellular Automata
We consider the problem of exhaustively visiting all pairs of linear cellular
automata which give rise to orthogonal Latin squares, i.e., linear Orthogonal
Cellular Automata (OCA). The problem is equivalent to enumerating all pairs of
coprime polynomials over a finite field having the same degree and a nonzero
constant term. While previous research showed how to count all such pairs for a
given degree and order of the finite field, no practical enumeration algorithms
have been proposed so far. Here, we start closing this gap by addressing the
case of polynomials defined over the field \F_2, which corresponds to binary
CA. In particular, we exploit Benjamin and Bennett's bijection between coprime
and non-coprime pairs of polynomials, which enables us to organize our study
along three subproblems, namely the enumeration and count of: (1) sequences of
constant terms, (2) sequences of degrees, and (3) sequences of intermediate
terms. In the course of this investigation, we unveil interesting connections
with algebraic language theory and combinatorics, obtaining an enumeration
algorithm and an alternative derivation of the counting formula for this
problem.Comment: 9 pages, 1 figure. Submitted to the exploratory track of AUTOMATA
2023. arXiv admin note: text overlap with arXiv:2207.0040
Quasi-adiabatic Switching for Metal-Island Quantum-dot Cellular Automata
Recent experiments have demonstrated a working cell suitable for implementing
the Quantum-dot Cellular Automata (QCA) paradigm. These experiments have been
performed using metal island clusters. The most promising approach to QCA
operation involves quasi-adiabatically switching the cells. This has been
analyzed extensively in gated semiconductor cells. Here we present a metal
island cell structure that makes quasi-adiabatic switching possible. We show
how this permits quasi-adiabatic clocking, and enables a pipelined
architecture.Comment: 40 preprint-style double-spaced pages including 16 figure
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