61,526 research outputs found
The Quantum Frontier
The success of the abstract model of computation, in terms of bits, logical
operations, programming language constructs, and the like, makes it easy to
forget that computation is a physical process. Our cherished notions of
computation and information are grounded in classical mechanics, but the
physics underlying our world is quantum. In the early 80s researchers began to
ask how computation would change if we adopted a quantum mechanical, instead of
a classical mechanical, view of computation. Slowly, a new picture of
computation arose, one that gave rise to a variety of faster algorithms, novel
cryptographic mechanisms, and alternative methods of communication. Small
quantum information processing devices have been built, and efforts are
underway to build larger ones. Even apart from the existence of these devices,
the quantum view on information processing has provided significant insight
into the nature of computation and information, and a deeper understanding of
the physics of our universe and its connections with computation.
We start by describing aspects of quantum mechanics that are at the heart of
a quantum view of information processing. We give our own idiosyncratic view of
a number of these topics in the hopes of correcting common misconceptions and
highlighting aspects that are often overlooked. A number of the phenomena
described were initially viewed as oddities of quantum mechanics. It was
quantum information processing, first quantum cryptography and then, more
dramatically, quantum computing, that turned the tables and showed that these
oddities could be put to practical effect. It is these application we describe
next. We conclude with a section describing some of the many questions left for
future work, especially the mysteries surrounding where the power of quantum
information ultimately comes from.Comment: Invited book chapter for Computation for Humanity - Information
Technology to Advance Society to be published by CRC Press. Concepts
clarified and style made more uniform in version 2. Many thanks to the
referees for their suggestions for improvement
Quantum computing and the entanglement frontier - Rapporteur talk at the 25th Solvay Conference
Quantum information science explores the frontier of highly complex quantum states,
the "entanglement frontier". This study is motivated by the observation (widely believed
but unproven) that classical systems cannot simulate highly entangled quantum systems
efficiently, and we hope to hasten the day when well controlled quantum systems can
perform tasks surpassing what can be done in the classical world. One way to achieve
such "quantum supremacy" would be to run an algorithm on a quantum computer which
solves a problem with a super-polynomial speedup relative to classical computers, but
there may be other ways that can be achieved sooner, such as simulating exotic quantum
states of strongly correlated matter. To operate a large scale quantum computer reliably
we will need to overcome the debilitating effects of decoherence, which might be done
using "standard" quantum hardware protected by quantum error-correcting codes, or by
exploiting the nonabelian quantum statistics of anyons realized in solid state systems,
or by combining both methods. Only by challenging the entanglement frontier will we
learn whether Nature provides extravagant resources far beyond what the classical world
would allow
Extremal Quantum Correlations: Experimental Study with Two-qubit States
We explore experimentally the space of two-qubit quantum correlated mixed
states, including frontier ones as defined by the use of quantum discord and
von Neumann entropy. Our experimental setup is flexible enough to allow for the
high-quality generation of a vast variety of states. We address quantitatively
the relation between quantum discord and a recently suggested alternative
measure of quantum correlations.Comment: 5 pages, 2 figure
Quantum algebraic representation of localization and motion of a Dirac electron
Quantum algebraic observables representing localization in space-time of a
Dirac electron are defined. Inertial motion of the electron is represented in
the quantum algebra with electron mass acting as the generator of motion. Since
transformations to uniformly accelerated frames are naturally included in this
conformally invariant description, the quantum algebra is also able to deal
with uniformly accelerated motion.Comment: 10 pages, Frontier Tests of QED and Physics of the Vacuum, Trieste,
5-11/10/200
New Approaches for ab initio Calculations of Molecules with Strong Electron Correlation
Reliable quantum chemical methods for the description of molecules with
dense-lying frontier orbitals are needed in the context of many chemical
compounds and reactions. Here, we review developments that led to our
newcomputational toolbo x which implements the quantum chemical density matrix
renormalization group in a second-generation algorithm. We present an overview
of the different components of this toolbox.Comment: 19 pages, 1 tabl
Quantum Fluctuations of the Gravitational Field and Propagation of Light: a Heuristic Approach
Quantum gravity is quite elusive at the experimental level; thus a lot of
interest has been raised by recent searches for quantum gravity effects in the
propagation of light from distant sources, like gamma ray bursters and active
galactic nuclei, and also in earth-based interferometers, like those used for
gravitational wave detection. Here we describe a simple heuristic picture of
the quantum fluctuations of the gravitational field that we have proposed
recently, and show how to use it to estimate quantum gravity effects in
interferometers.Comment: LaTeX2e, 8 pages, 2 eps figures: Talk presented at QED2000, 2nd
Workshop on Frontier Tests of Quantum Electrodynamics and Physics of the
Vacuum; included in conference proceeding
Pseudoscalar production in electromagnetic fields by a Schwinger-like mechanism
In this talk I report on some recent calculations on the production of
pseudoscalars from intense electromagnetic fields.Comment: 5 pages, Invited talk at QED2000, 2nd Workshop on Frontier Tests of
Quantum Electrodynamics and Physics of the Vacuum, Trieste (October 2000
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