5,509 research outputs found
Cellular Automata as a Model of Physical Systems
Cellular Automata (CA), as they are presented in the literature, are abstract
mathematical models of computation. In this pa- per we present an alternate
approach: using the CA as a model or theory of physical systems and devices.
While this approach abstracts away all details of the underlying physical
system, it remains faithful to the fact that there is an underlying physical
reality which it describes. This imposes certain restrictions on the types of
computations a CA can physically carry out, and the resources it needs to do
so. In this paper we explore these and other consequences of our
reformalization.Comment: To appear in the Proceedings of AUTOMATA 200
What is a quantum computer, and how do we build one?
The DiVincenzo criteria for implementing a quantum computer have been seminal
in focussing both experimental and theoretical research in quantum information
processing. These criteria were formulated specifically for the circuit model
of quantum computing. However, several new models for quantum computing
(paradigms) have been proposed that do not seem to fit the criteria well. The
question is therefore what are the general criteria for implementing quantum
computers. To this end, a formal operational definition of a quantum computer
is introduced. It is then shown that according to this definition a device is a
quantum computer if it obeys the following four criteria: Any quantum computer
must (1) have a quantum memory; (2) facilitate a controlled quantum evolution
of the quantum memory; (3) include a method for cooling the quantum memory; and
(4) provide a readout mechanism for subsets of the quantum memory. The criteria
are met when the device is scalable and operates fault-tolerantly. We discuss
various existing quantum computing paradigms, and how they fit within this
framework. Finally, we lay out a roadmap for selecting an avenue towards
building a quantum computer. This is summarized in a decision tree intended to
help experimentalists determine the most natural paradigm given a particular
physical implementation
Models of Quantum Cellular Automata
In this paper we present a systematic view of Quantum Cellular Automata
(QCA), a mathematical formalism of quantum computation. First we give a general
mathematical framework with which to study QCA models. Then we present four
different QCA models, and compare them. One model we discuss is the traditional
QCA, similar to those introduced by Shumacher and Werner, Watrous, and Van Dam.
We discuss also Margolus QCA, also discussed by Schumacher and Werner. We
introduce two new models, Coloured QCA, and Continuous-Time QCA. We also
compare our models with the established models. We give proofs of computational
equivalence for several of these models. We show the strengths of each model,
and provide examples of how our models can be useful to come up with
algorithms, and implement them in real-world physical devices
The extremely asymmetric radio structure of the z=3.1 radio galaxy B3 J2330+3927
We report on 1.7 and 5.0 GHz observations of the z=3.087 radio galaxy B3
J2330+3927, using the Very Long Baseline Array (VLBA), and archival 1.4 and 8.4
GHz Very Large Array (VLA) data. Our VLBA data identify a compact, flat
spectrum (\alpha_{1.7 GHz}^{5 GHz} = -0.2 +/- 0.1; S_\nu ~ \nu^\alpha) radio
component as the core. The VLA images show that the fraction of core emission
is very large (f_c \approx 0.5 at 8.4 GHz), and reveal a previously undetected,
very faint counterjet, implying a radio lobe flux density ratio R >= 11 and a
radio lobe distance ratio Q \approx 1.9. Those values are much more common in
quasars than in radio galaxies, but the optical/near-IR spectra show a clear
type II AGN for B3 J2330+3927, confirming that it is indeed a radio galaxy.
Unlike all other radio galaxies, the bright Ly-\alpha emitting gas is located
towards the furthest radio arm. We argue against environmental and relativistic
beaming effects being the cause of the observed asymmetry, and suggest this
source has intrinsically asymmetric radio jets. If this is the case, B3
J2330+3927 is the first example of such a source at high redshift, and seems to
be difficult to reconcile with the unified model, which explains the
differences between quasars and radio galaxies as being due to orientation
effects.Comment: 6 pages, 3 figures, to appear as a Letter to MNRA
Single spin measurement using cellular automata techniques
We propose an approach for single spin measurement. Our method uses
techniques from the theory of quantum cellular automata to correlate a large
amount of ancillary spins to the one to be measured. It has the distinct
advantage of being efficient, and to a certain extent fault-tolerant. Under
ideal conditions, it requires the application of only order of cube root of N
steps (each requiring a constant number of rf pulses) to create a system of N
correlated spins. It is also fairly robust against pulse errors, imperfect
initial polarization of the ancilla spin system, and does not rely on
entanglement. We study the scalability of our scheme through numerical
simulation.Comment: Submitted to Physical Review Letter
Management System for Harvest Scheduling: The Case of Horticultural Production in Southeast Spain
horticultural farmer, optimization, planning, mathematical programming, marketing, cooperative, Agribusiness, Crop Production/Industries, Demand and Price Analysis, Farm Management, Land Economics/Use,
Quantum Blockchain Miners Provide Massive Energy Savings
Blockchain-based cryptocurrencies have become an extremely important,
highly-used, technology. A major criticism of cryptocurrencies, however, is
their energy consumption. In May 2022 Bitcoin alone was reported to be
consuming 150 terawatt-hours of electricity annually; more than many entire
countries. Hence, any meaningful efficiency increase in this process would have
a tremendous positive impact. Meanwhile, practical applications of quantum
information technologies, and in particular of near-term quantum computers
(NISQ) continue to be an important research question. Here, we study the
efficiency benefits of moving cryptocurrency mining from current ASIC-based
miners to quantum, and in particular NISQ, miners. While the time-efficiency
benefits of quantum technologies is extremely well-studied, here we focus on
energy savings. We show that the transition to quantum-based mining could incur
an energy saving, by relatively conservative estimates, of about roughly
126.7TWH, or put differently the total energy consumption of Sweden in 2020
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