1,808 research outputs found
Finite-Block-Length Analysis in Classical and Quantum Information Theory
Coding technology is used in several information processing tasks. In
particular, when noise during transmission disturbs communications, coding
technology is employed to protect the information. However, there are two types
of coding technology: coding in classical information theory and coding in
quantum information theory. Although the physical media used to transmit
information ultimately obey quantum mechanics, we need to choose the type of
coding depending on the kind of information device, classical or quantum, that
is being used. In both branches of information theory, there are many elegant
theoretical results under the ideal assumption that an infinitely large system
is available. In a realistic situation, we need to account for finite size
effects. The present paper reviews finite size effects in classical and quantum
information theory with respect to various topics, including applied aspects
A high-speed multi-protocol quantum key distribution transmitter based on a dual-drive modulator
We propose a novel source based on a dual-drive modulator that is adaptable
and allows Alice to choose between various practical quantum key distribution
(QKD) protocols depending on what receiver she is communicating with.
Experimental results show that the proposed transmitter is suitable for
implementation of the Bennett and Brassard 1984 (BB84), coherent one-way (COW)
and differential phase shift (DPS) protocols with stable and low quantum bit
error rate. This could become a useful component in network QKD, where
multi-protocol capability is highly desirable.Comment: 15 pages, 7 figure
Quantum Repeater with Encoding
We propose a new approach to implement quantum repeaters for long distance
quantum communication. Our protocol generates a backbone of encoded Bell pairs
and uses the procedure of classical error correction during simultaneous
entanglement connection. We illustrate that the repeater protocol with simple
Calderbank-Shor-Steane (CSS) encoding can significantly extend the
communication distance, while still maintaining a fast key generation rate.Comment: 11 pages, 5 figures (add new section III with an explicit example and
new appendix A
Security of quantum key distribution protocols using two-way classical communication or weak coherent pulses
We apply the techniques introduced in [Kraus et. al., Phys. Rev. Lett. 95,
080501, 2005] to prove security of quantum key distribution (QKD) schemes using
two-way classical post-processing as well as QKD schemes based on weak coherent
pulses instead of single-photon pulses. As a result, we obtain improved bounds
on the secret-key rate of these schemes
Quantum entanglement
All our former experience with application of quantum theory seems to say:
{\it what is predicted by quantum formalism must occur in laboratory}. But the
essence of quantum formalism - entanglement, recognized by Einstein, Podolsky,
Rosen and Schr\"odinger - waited over 70 years to enter to laboratories as a
new resource as real as energy.
This holistic property of compound quantum systems, which involves
nonclassical correlations between subsystems, is a potential for many quantum
processes, including ``canonical'' ones: quantum cryptography, quantum
teleportation and dense coding. However, it appeared that this new resource is
very complex and difficult to detect. Being usually fragile to environment, it
is robust against conceptual and mathematical tools, the task of which is to
decipher its rich structure.
This article reviews basic aspects of entanglement including its
characterization, detection, distillation and quantifying. In particular, the
authors discuss various manifestations of entanglement via Bell inequalities,
entropic inequalities, entanglement witnesses, quantum cryptography and point
out some interrelations. They also discuss a basic role of entanglement in
quantum communication within distant labs paradigm and stress some
peculiarities such as irreversibility of entanglement manipulations including
its extremal form - bound entanglement phenomenon. A basic role of entanglement
witnesses in detection of entanglement is emphasized.Comment: 110 pages, 3 figures, ReVTex4, Improved (slightly extended)
presentation, updated references, minor changes, submitted to Rev. Mod. Phys
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