451 research outputs found
Quantum Cellular Automata
Quantum cellular automata (QCA) are reviewed, including early and more recent
proposals. QCA are a generalization of (classical) cellular automata (CA) and
in particular of reversible CA. The latter are reviewed shortly. An overview is
given over early attempts by various authors to define one-dimensional QCA.
These turned out to have serious shortcomings which are discussed as well.
Various proposals subsequently put forward by a number of authors for a general
definition of one- and higher-dimensional QCA are reviewed and their properties
such as universality and reversibility are discussed.Comment: 12 pages, 3 figures. To appear in the Springer Encyclopedia of
Complexity and Systems Scienc
Entanglement Dynamics in 1D Quantum Cellular Automata
Several proposed schemes for the physical realization of a quantum computer
consist of qubits arranged in a cellular array. In the quantum circuit model of
quantum computation, an often complex series of two-qubit gate operations is
required between arbitrarily distant pairs of lattice qubits. An alternative
model of quantum computation based on quantum cellular automata (QCA) requires
only homogeneous local interactions that can be implemented in parallel. This
would be a huge simplification in an actual experiment. We find some minimal
physical requirements for the construction of unitary QCA in a 1 dimensional
Ising spin chain and demonstrate optimal pulse sequences for information
transport and entanglement distribution. We also introduce the theory of
non-unitary QCA and show by example that non-unitary rules can generate
environment assisted entanglement.Comment: 12 pages, 8 figures, submitted to Physical Review
Electron Spin for Classical Information Processing: A Brief Survey of Spin-Based Logic Devices, Gates and Circuits
In electronics, information has been traditionally stored, processed and
communicated using an electron's charge. This paradigm is increasingly turning
out to be energy-inefficient, because movement of charge within an
information-processing device invariably causes current flow and an associated
dissipation. Replacing charge with the "spin" of an electron to encode
information may eliminate much of this dissipation and lead to more
energy-efficient "green electronics". This realization has spurred significant
research in spintronic devices and circuits where spin either directly acts as
the physical variable for hosting information or augments the role of charge.
In this review article, we discuss and elucidate some of these ideas, and
highlight their strengths and weaknesses. Many of them can potentially reduce
energy dissipation significantly, but unfortunately are error-prone and
unreliable. Moreover, there are serious obstacles to their technological
implementation that may be difficult to overcome in the near term.
This review addresses three constructs: (1) single devices or binary switches
that can be constituents of Boolean logic gates for digital information
processing, (2) complete gates that are capable of performing specific Boolean
logic operations, and (3) combinational circuits or architectures (equivalent
to many gates working in unison) that are capable of performing universal
computation.Comment: Topical Revie
Cellular Structures for Computation in the Quantum Regime
We present a new cellular data processing scheme, a hybrid of existing
cellular automata (CA) and gate array architectures, which is optimized for
realization at the quantum scale. For conventional computing, the CA-like
external clocking avoids the time-scale problems associated with ground-state
relaxation schemes. For quantum computing, the architecture constitutes a novel
paradigm whereby the algorithm is embedded in spatial, as opposed to temporal,
structure. The architecture can be exploited to produce highly efficient
algorithms: for example, a list of length N can be searched in time of order
cube root N.Comment: 11 pages (LaTeX), 3 figure
Quantum cellular automata quantum computing with endohedral fullerenes
We present a scheme to perform universal quantum computation using global
addressing techniques as applied to a physical system of endohedrally doped
fullerenes. The system consists of an ABAB linear array of Group V endohedrally
doped fullerenes. Each molecule spin site consists of a nuclear spin coupled
via a Hyperfine interaction to an electron spin. The electron spin of each
molecule is in a quartet ground state . Neighboring molecular electron
spins are coupled via a magnetic dipole interaction. We find that an
all-electron construction of a quantum cellular automata is frustrated due to
the degeneracy of the electronic transitions. However, we can construct a
quantum celluar automata quantum computing architecture using these molecules
by encoding the quantum information on the nuclear spins while using the
electron spins as a local bus. We deduce the NMR and ESR pulses required to
execute the basic cellular automata operation and obtain a rough figure of
merit for the the number of gate operations per decoherence time. We find that
this figure of merit compares well with other physical quantum computer
proposals. We argue that the proposed architecture meets well the first four
DiVincenzo criteria and we outline various routes towards meeting the fifth
criteria: qubit readout.Comment: 16 pages, Latex, 5 figures, See http://planck.thphys.may.ie/QIPDDF/
submitted to Phys. Rev.
QCA-Based Majority Gate Design under Radius of Effect-Induced Faults
This paper presents reliable QCA cell structures for designing single clock-controlled majority gates with a tolerance to radius of effect-induced faults, for use as a basic building component for carry look-ahead adder. Realizable quantum computing is still well in the future due to the complexity of the quantum mechanics that govern them. In this regard, QCA-based system design is a challenging task since each cell\u27\u27s state must interact with all the cells that are in its energy-effective range in its clocking zone, referred to as its radius of effect. This paper proposes a design approach for majority gates to overcome the constraints imposed by the radius of effect of each cell with respect to clock controls. Radius of effect induces faults that lead to constraints on the clocking scheme of majority gates. We show majority gate structures that operate with multiple radius of effect-induced faults under a single clock control. The proposed design approach to a single clock controlled majority gate ultimately facilitate more efficient and flexible clocking schemes for complex QCA designs
Synthesis and Optimization of Reversible Circuits - A Survey
Reversible logic circuits have been historically motivated by theoretical
research in low-power electronics as well as practical improvement of
bit-manipulation transforms in cryptography and computer graphics. Recently,
reversible circuits have attracted interest as components of quantum
algorithms, as well as in photonic and nano-computing technologies where some
switching devices offer no signal gain. Research in generating reversible logic
distinguishes between circuit synthesis, post-synthesis optimization, and
technology mapping. In this survey, we review algorithmic paradigms ---
search-based, cycle-based, transformation-based, and BDD-based --- as well as
specific algorithms for reversible synthesis, both exact and heuristic. We
conclude the survey by outlining key open challenges in synthesis of reversible
and quantum logic, as well as most common misconceptions.Comment: 34 pages, 15 figures, 2 table
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