202,314 research outputs found
Philosophical Aspects of Quantum Information Theory
Quantum information theory represents a rich subject of discussion for those
interested in the philosphical and foundational issues surrounding quantum
mechanics for a simple reason: one can cast its central concerns in terms of a
long-familiar question: How does the quantum world differ from the classical
one? Moreover, deployment of the concepts of information and computation in
novel contexts hints at new (or better) means of understanding quantum
mechanics, and perhaps even invites re-assessment of traditional material
conceptions of the basic nature of the physical world. In this paper I review
some of these philosophical aspects of quantum information theory, begining
with an elementary survey of the theory, seeking to highlight some of the
principles and heuristics involved. We move on to a discussion of the nature
and definition of quantum information and deploy the findings in discussing the
puzzles surrounding teleportation. The final two sections discuss,
respectively, what one might learn from the development of quantum computation
(both about the nature of quantum systems and about the nature of computation)
and consider the impact of quantum information theory on the traditional
foundational questions of quantum mechanics (treating of the views of
Zeilinger, Bub and Fuchs, amongst others).Comment: LaTeX; 55pp; 3 figs. Forthcoming in Rickles (ed.) The Ashgate
Companion to the New Philosophy of Physic
Black Holes: Eliminating Information or Illuminating New Physics?
Black holes, initially thought of as very interesting geometric constructions
of nature, over time, have learnt to (often) come up with surprises and
challenges. From the era of being described as merely some interesting and
exotic solutions of \gr, they have, in modern times, really started to test our
confidence in everything else, we thought we know about the nature. They have
in this process, also earned a dreadsome reputation in some corners of
theoretical physics. The most serious charge on the black holes is that they
eat up information, never to release and subsequently erase it. This goes
absolutely against the sacred principles of all other branches of fundamental
sciences. This realization has shaken the very base of foundational concepts,
both in quantum theory and gravity, which we always took for granted. Attempts
to exorcise black holes of this charge, have led us to crossroads with
concepts, hold dearly in quantum theory. The sphere of black hole's tussle with
quantum theory has readily and steadily grown, from the advent of the Hawking
radiation some four decades back, into domain of quantum information theory in
modern times, most aptly, recently put in the form of the firewall puzzle. Do
black holes really indicate something sinister about their existence or do they
really take the lid off our comfort with ignoring the fundamental issues, our
modern theories are seemingly plagued with? In this review, we focus on issues
pertaining to black hole evaporation, the development of the information loss
paradox, its recent formulation, the leading debates and promising directions
in the community.Comment: Published in Univers
Quantum processes
A number of ideas and questions related to the construction of quantum
processes are discussed. Quantum state extension, entanglement and asymptotic
behaviour of the entropy are some of the issues explored. These topics are
studied in more detail for a class of quantum processes known as finitely
correlated states. Several examples of such processes are presented,
specifically a Free Fermionic model.Comment: 20 pages, 2 figures, to appear in the proceedings of the 46th Karpacz
Winter School of Theoretical Physics "Quantum Dynamics and Information:
Theory and Experiment
How far can a pragmatist go into quantum theory? - A critical view of our current understanding of quantum phenomena
To date, quantum mechanics has proven to be our most successful theoretical
model. However, it is still surrounded by a "mysterious halo" that can be
summarized in a simple but challenging question: Why quantum phenomena are not
understood under the same logic as classical ones? Although this is an open
question (probably without an answer), from a pragmatist's point of view there
is still room enough to further explore the quantum world, marveling ourselves
with new physical insights. We just need to look back in the historical
evolution of the quantum theory and thoroughly reconsider three key issues: (1)
how this has developed since its early stages at a conceptual level, (2) what
kind of experiments can be performed at present in a laboratory, and (3) what
nonstandard conceptual models are available to extract some extra information.
This contribution is aimed at providing some answers (and, perhaps, also
raising some issues) to these questions through one of such models, namely
Bohmian mechanics, a hydrodynamic formulation of the quantum theory, which is
currently trying to open new pathways of understanding. Specifically, the
Chapter constitutes a brief and personal overview on the historic and
contextual evolution of this quantum formulation, its physical meaning and
interest (leaving aside metaphysical issues), and how it may help to overcome
some preconceived paradoxical aspects of the quantum theory.Comment: 11 pages, 2 figures; contribution to "Particle and Astroparticle
Physics, Gravitation and Cosmology: Predictions, Observations and New
Projects" (Proceedings of the XXXth International Workshop on High Energy
Physics), eds. V. Petrov and R. Ryutin (World Scientific, Singapore, 2015),
pp. 161-17
The Quantum PCP Conjecture
The classical PCP theorem is arguably the most important achievement of
classical complexity theory in the past quarter century. In recent years,
researchers in quantum computational complexity have tried to identify
approaches and develop tools that address the question: does a quantum version
of the PCP theorem hold? The story of this study starts with classical
complexity and takes unexpected turns providing fascinating vistas on the
foundations of quantum mechanics, the global nature of entanglement and its
topological properties, quantum error correction, information theory, and much
more; it raises questions that touch upon some of the most fundamental issues
at the heart of our understanding of quantum mechanics. At this point, the jury
is still out as to whether or not such a theorem holds. This survey aims to
provide a snapshot of the status in this ongoing story, tailored to a general
theory-of-CS audience.Comment: 45 pages, 4 figures, an enhanced version of the SIGACT guest column
from Volume 44 Issue 2, June 201
On the quantumness of correlations in nuclear magnetic resonance
Nuclear Magnetic Resonance (NMR) was successfully employed to test several
protocols and ideas in Quantum Information Science. In most of these
implementations the existence of entanglement was ruled out. This fact
introduced concerns and questions about the quantum nature of such bench tests.
In this article we address some issues related to the non-classical aspects of
NMR systems. We discuss some experiments where the quantum aspects of this
system are supported by quantum correlations of separable states. Such
quantumness, beyond the entanglement-separability paradigm, is revealed via a
departure between the quantum and the classical versions of information theory.
In this scenario, the concept of quantum discord seems to play an important
role. We also present an experimental implementation of an analogous of the
single-photon Mach-Zehnder interferometer employing two nuclear spins to encode
the interferometric paths. This experiment illustrate how non-classical
correlations of separable states may be used to simulate quantum dynamics. The
results obtained are completely equivalent to the optical scenario, where
entanglement (between two field modes) may be present
Quantum Riemannian Geometry and Black Holes
Black Holes have always played a central role in investigations of quantum
gravity. This includes both conceptual issues such as the role of classical
singularities and information loss, and technical ones to probe the consistency
of candidate theories. Lacking a full theory of quantum gravity, such studies
had long been restricted to black hole models which include some aspects of
quantization. However, it is then not always clear whether the results are
consequences of quantum gravity per se or of the particular steps one had
undertaken to bring the system into a treatable form. Over a little more than
the last decade loop quantum gravity has emerged as a widely studied candidate
for quantum gravity, where it is now possible to introduce black hole models
within a quantum theory of gravity. This makes it possible to use only quantum
effects which are known to arise also in the full theory, but still work in a
rather simple and physically interesting context of black holes. Recent
developments have now led to the first physical results about non-rotating
quantum black holes obtained in this way. Restricting to the interior inside
the Schwarzschild horizon, the resulting quantum model is free of the classical
singularity, which is a consequence of discrete quantum geometry taking over
for the continuous classical space-time picture. This fact results in a change
of paradigm concerning the information loss problem. The horizon itself can
also be studied in the quantum theory by imposing horizon conditions at the
level of states. Thereby one can illustrate the nature of horizon degrees of
freedom and horizon fluctuations. All these developments allow us to study the
quantum dynamics explicitly and in detail which provides a rich ground to test
the consistency of the full theory.Comment: 45 pages, 4 figures, chapter of "Trends in Quantum Gravity Research"
(Nova Science
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