12,895 research outputs found
Silicon Atomic Quantum Dots Enable Beyond-CMOS Electronics
We review our recent efforts in building atom-scale quantum-dot cellular
automata circuits on a silicon surface. Our building block consists of silicon
dangling bond on a H-Si(001) surface, which has been shown to act as a quantum
dot. First the fabrication, experimental imaging, and charging character of the
dangling bond are discussed. We then show how precise assemblies of such dots
can be created to form artificial molecules. Such complex structures can be
used as systems with custom optical properties, circuit elements for
quantum-dot cellular automata, and quantum computing. Considerations on
macro-to-atom connections are discussed.Comment: 28 pages, 19 figure
Two-tape finite automata with quantum and classical states
{\it Two-way finite automata with quantum and classical states} (2QCFA) were
introduced by Ambainis and Watrous, and {\it two-way two-tape deterministic
finite automata} (2TFA) were introduced by Rabin and Scott. In this paper we
study 2TFA and propose a new computing model called {\it two-way two-tape
finite automata with quantum and classical states} (2TQCFA). First, we give
efficient 2TFA algorithms for recognizing languages which can be recognized by
2QCFA. Second, we give efficient 2TQCFA algorithms to recognize several
languages whose status vis-a-vis 2QCFA have been posed as open questions, such
as . Third, we show that
can be recognized by {\it -tape
deterministic finite automata} (TFA). Finally, we introduce {\it
-tape automata with quantum and classical states} (TQCFA) and prove that
can be recognized by TQCFA.Comment: 25 page
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
Charge-to-spin conversion of electron entanglement states and spin-interaction-free solid-state quantum computation
Without resorting to spin-spin coupling, we propose a scalable spin quantum
computing scheme assisted with a semiconductor multiple-quantum-dot structure.
The techniques of single electron transitions and the nanostructure of
quantum-dot cellular automata (QCA) are used to generate charge entangled
states of two electrons, which are then converted into spin entanglement states
using single-spin rotations only. Deterministic two-qubit quantum gates are
also manipulated using only single-spin rotations with the help of QCA. A
single-shot readout of spin states can be carried out by coupling the multiple
dot structure to a quantum point contact. As a result, deterministic
spin-interaction-free quantum computing can be implemented in semiconductor
nanostructure.Comment: 5 pages, 4 figures, the revised version of quant-ph/0502002 for
publication in Phys. Rev. B (to be appear on the issue of Oct. 15, 2007
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.
Interference Automata
We propose a computing model, the Two-Way Optical Interference Automata
(2OIA), that makes use of the phenomenon of optical interference. We introduce
this model to investigate the increase in power, in terms of language
recognition, of a classical Deterministic Finite Automaton (DFA) when endowed
with the facility of optical interference. The question is in the spirit of
Two-Way Finite Automata With Quantum and Classical States (2QCFA) [A. Ambainis
and J. Watrous, Two-way Finite Automata With Quantum and Classical States,
Theoretical Computer Science, 287 (1), 299-311, (2002)] wherein the classical
DFA is augmented with a quantum component of constant size. We test the power
of 2OIA against the languages mentioned in the above paper. We give efficient
2OIA algorithms to recognize languages for which 2QCFA machines have been shown
to exist, as well as languages whose status vis-a-vis 2QCFA has been posed as
open questions. Finally we show the existence of a language that cannot be
recognized by a 2OIA but can be recognized by an space Turing machine.Comment: 19 pages. A preliminary version appears under the title "On a Model
of Computation based on Optical Interference" in Proc. of the 16-th
Australasian Workshop on Combinatorial Algorithms (AWOCA'05), pp. 249-26
Quantum-Dot Cellular Automata using Buried Dopants
The use of buried dopants to construct quantum-dot cellular automata is
investigated as an alternative to conventional electronic devices for
information transport and elementary computation. This provides a limit in
terms of miniaturisation for this type of system as each potential well is
formed by a single dopant atom. As an example, phosphorous donors in silicon
are found to have good energy level separation with incoherent switching times
of the order of microseconds. However, we also illustrate the possibility of
ultra-fast quantum coherent switching via adiabatic evolution. The switching
speeds are numerically calculated and found to be 10's of picoseconds or less
for a single cell. The effect of decoherence is also simulated in the form of a
dephasing process and limits are estimated for operation with finite dephasing.
The advantages and limitations of this scheme over the more conventional
quantum-dot based scheme are discussed. The use of a buried donor cellular
automata system is also discussed as an architecture for testing several
aspects of buried donor based quantum computing schemes.Comment: Minor changes in response to referees comments. Improved section on
scaling and added plot of incoherent switching time
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