11,707 research outputs found
An Introduction to Quantum Computing for Non-Physicists
Richard Feynman's observation that quantum mechanical effects could not be
simulated efficiently on a computer led to speculation that computation in
general could be done more efficiently if it used quantum effects. This
speculation appeared justified when Peter Shor described a polynomial time
quantum algorithm for factoring integers.
In quantum systems, the computational space increases exponentially with the
size of the system which enables exponential parallelism. This parallelism
could lead to exponentially faster quantum algorithms than possible
classically. The catch is that accessing the results, which requires
measurement, proves tricky and requires new non-traditional programming
techniques.
The aim of this paper is to guide computer scientists and other
non-physicists through the conceptual and notational barriers that separate
quantum computing from conventional computing. We introduce basic principles of
quantum mechanics to explain where the power of quantum computers comes from
and why it is difficult to harness. We describe quantum cryptography,
teleportation, and dense coding. Various approaches to harnessing the power of
quantum parallelism are explained, including Shor's algorithm, Grover's
algorithm, and Hogg's algorithms. We conclude with a discussion of quantum
error correction.Comment: 45 pages. To appear in ACM Computing Surveys. LATEX file. Exposition
improved throughout thanks to reviewers' comment
A Gentle Introduction to Quantum Computing Algorithms with Applications to Universal Prediction
In this technical report we give an elementary introduction to Quantum
Computing for non-physicists. In this introduction we describe in detail some
of the foundational Quantum Algorithms including: the Deutsch-Jozsa Algorithm,
Shor's Algorithm, Grocer Search, and Quantum Counting Algorithm and briefly the
Harrow-Lloyd Algorithm. Additionally we give an introduction to Solomonoff
Induction, a theoretically optimal method for prediction. We then attempt to
use Quantum computing to find better algorithms for the approximation of
Solomonoff Induction. This is done by using techniques from other Quantum
computing algorithms to achieve a speedup in computing the speed prior, which
is an approximation of Solomonoff's prior, a key part of Solomonoff Induction.
The major limiting factors are that the probabilities being computed are often
so small that without a sufficient (often large) amount of trials, the error
may be larger than the result. If a substantial speedup in the computation of
an approximation of Solomonoff Induction can be achieved through quantum
computing, then this can be applied to the field of intelligent agents as a key
part of an approximation of the agent AIXI
Entangled states of light
These notes are more or less a faithful representation of my talk at the
Workshop on ``Quantum Coding and Quantum Computing'' held at the University of
Virginia. As such it is an introduction for non-physicists to the topics of the
quantum theory of light and entangled states of light. In particular, I discuss
the photon concept and what is really entangled in an entangled state of light
(it is not the photons). Moreover, I discuss an example that highlights the
peculiar behavior of entanglement in an infinite-dimensional Hilbert space.Comment: 5 pages, 1 figure, notes of my talk at the Workshop on ``Quantum
Coding and Quantum Computing'' held at the University of Virgini
Free Will - A road less travelled in quantum information
Conway and Kochen's Free Will Theory is examined as an important foundational
element in a new area of activity in computer science - developing protocols
for quantum computingComment: 18 pages including reference
Yet another time about time - Part I
This paper presents yet another personal reflection on one the most important
concepts in both science and the humanities: time. This elusive notion has been
not only bothering philosophers since Plato and Aristotle. It goes throughout
human history embracing all analytical and creative (anthropocentric)
disciplines. Time has been a central theme in physical and life sciences,
philosophy, psychology, music, art and many more. This theme is known with a
vast body of knowledge across different theories and categories. What has been
explored concerns its nature (rational, irrational, arational),
appearances/qualia, degrees, dimensions and scales of conceptualization
(internal, external, fractal, discrete, continuous, mechanical, quantum, local,
global, etc.). Of particular interest have been parameters of time such as
duration ranges, resolutions, modes (present, now, past, future), varieties of
tenses (e.g. present perfect, present progressive, etc.) and some intuitive,
but also fancy phenomenological characteristics such as arrow, stream, texture,
width, depth, density, even scent. Perhaps the most distinct characteristic of
this fundamental concept is the absolute time constituting the flow of
consciousness according to Husserl, the reflection of pure (human) nature
without having the distinction between exo and endo. This essay is a personal
reflection upon the meaning of time in modern physics and phenomenological
philosophy.Comment: 35 pages, 1 figures, to be published in: J. Progress in Biophysics
and Molecular Biology. Vol. 119, Issue 2. Special Theme Issue on Integral
Biomathics: Life Sciences, Mathematics, and Phenomenological Philosophy.
Elsevier. ISSN: 0079-6107, Progress in Biophysics and Molecular Biology, Vol.
119, Issue 2, 201
Quantum entanglement
Expository paper providing a historical survey of the gradual transformation
of the "philosophical discussions" between Bohr, Einstein and Schr\"odinger on
foundational issues in quantum mechanics into a quantitative prediction of a
new quantum effect, its experimental verification and its proposed (and loudly
advertised) applications. The basic idea of the 1935 paper of
Einstein-Podolsky-Rosen (EPR) was reformulated by David Bohm for a finite
dimensional spin system. This allowed John Bell to derive his inequalities that
separate the prediction of quantum entanglement from its possible classical
interpretation. We reproduce here their later (1971) version, reviewing on the
way the generalization (and mathematical derivation) of Heisenberg's
uncertainty relations (due to Weyl and Schr\"odinger) needed for the passage
from EPR to Bell. We also provide an improved derivation of the quantum
theoretic violation of Bell's inequalities. Soon after the experimental
confirmation of the quantum entanglement (culminating with the work of Alain
Aspect) it was Feynman who made public the idea of a quantum computer based on
the observed effect.Comment: 15 pages, 2 figures. Dedicated to the memory of Professor Christo
Christov (1915-1990
Machine Learning for Condensed Matter Physics
Condensed Matter Physics (CMP) seeks to understand the microscopic
interactions of matter at the quantum and atomistic levels, and describes how
these interactions result in both mesoscopic and macroscopic properties. CMP
overlaps with many other important branches of science, such as Chemistry,
Materials Science, Statistical Physics, and High-Performance Computing. With
the advancements in modern Machine Learning (ML) technology, a keen interest in
applying these algorithms to further CMP research has created a compelling new
area of research at the intersection of both fields. In this review, we aim to
explore the main areas within CMP, which have successfully applied ML
techniques to further research, such as the description and use of ML schemes
for potential energy surfaces, the characterization of topological phases of
matter in lattice systems, the prediction of phase transitions in off-lattice
and atomistic simulations, the interpretation of ML theories with
physics-inspired frameworks and the enhancement of simulation methods with ML
algorithms. We also discuss in detail the main challenges and drawbacks of
using ML methods on CMP problems, as well as some perspectives for future
developments.Comment: 48 pages, 2 figures, 300 references. Review paper. Major Revisio
Is Planck's Constant h a "Quantum" Constant? An Alternative Classical Interpretation
Although Planck's constant h is currently regarded as the elementary quantum
of action appearing in quantum theory, it can also be interpreted as the
multiplicative scale factor setting the scale of classical zero-point radiation
appearing in classical electromagnetic theory. Relativistic classical electron
theory with classical electromagnetic zero-point radiation gives many results
in agreement with quantum theory. The areas of agreement between this classical
theory and Nature seem worth further investigation.Comment: 10 page
mc4qcd: Online Analysis Tool for Lattice QCD
mc4qcd is a web based collaboration tool for analysis of Lattice QCD data.
Lattice QCD computations consists of a large scale Markov Chain Monte Carlo.
Multiple measurements are performed at each MC step. Our system acquires the
data by uploading log files, parses them for results of measurements, filters
the data, mines for required information by aggregating results, represents the
results as plots and histograms, and it further allows refining and interaction
by fitting the results. The system computes moving averages and
autocorrelations, builds bootstrap samples and bootstrap errors, and allows
modeling the data using Bayesian correlated constrained linear and non-linear
fits. It can be scripted to allow real time visualization of results form an
ongoing computation. The system is modular and it can be adapted to automating
the analysis workflow of different types of MC computations
Quantum computation and hidden variables
Many physicists limit oneself to an instrumentalist description of quantum
phenomena and ignore the problems of foundation and interpretation of quantum
mechanics. This instrumentalist approach results to "specialization barbarism"
and mass delusion concerning the problem, how a quantum computer can be made.
The idea of quantum computation can be described within the limits of quantum
formalism. But in order to understand how this idea can be put into practice
one should realize the question: "What could the quantum formalism describe?",
in spite of the absence of an universally recognized answer. Only a realization
of this question and the undecided problem of quantum foundations allows to see
in which quantum systems the superposition and EPR correlation could be
expected. Because of the "specialization barbarism" many authors are sure that
Bell proved full impossibility of any hidden-variables interpretation.
Therefore it is important to emphasize that in reality Bell has restricted to
validity limits of the no- hidden-variables proof and has shown that two-state
quantum system can be described by hidden variables. The later means that no
experimental result obtained on two-state quantum system can prove the
existence of superposition and violation of the realism. One should not assume
before unambiguous experimental evidence that any two-state quantum system is
quantum bit. No experimental evidence of superposition of macroscopically
distinct quantum states and of a quantum bit on base of superconductor
structure was obtained for the present. Moreover same experimental results can
not be described in the limits of the quantum formalism.Comment: 15 pages, 3 figures, The talk presented at the International
Symposium "Quantum Informatics-2007" Zvenigorod, Moscow region, Russia, 200
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