7,313 research outputs found
Continuous Variable Quantum Cryptography using Two-Way Quantum Communication
Quantum cryptography has been recently extended to continuous variable
systems, e.g., the bosonic modes of the electromagnetic field. In particular,
several cryptographic protocols have been proposed and experimentally
implemented using bosonic modes with Gaussian statistics. Such protocols have
shown the possibility of reaching very high secret-key rates, even in the
presence of strong losses in the quantum communication channel. Despite this
robustness to loss, their security can be affected by more general attacks
where extra Gaussian noise is introduced by the eavesdropper. In this general
scenario we show a "hardware solution" for enhancing the security thresholds of
these protocols. This is possible by extending them to a two-way quantum
communication where subsequent uses of the quantum channel are suitably
combined. In the resulting two-way schemes, one of the honest parties assists
the secret encoding of the other with the chance of a non-trivial superadditive
enhancement of the security thresholds. Such results enable the extension of
quantum cryptography to more complex quantum communications.Comment: 12 pages, 7 figures, REVTe
Gaussian Quantum Information
The science of quantum information has arisen over the last two decades
centered on the manipulation of individual quanta of information, known as
quantum bits or qubits. Quantum computers, quantum cryptography and quantum
teleportation are among the most celebrated ideas that have emerged from this
new field. It was realized later on that using continuous-variable quantum
information carriers, instead of qubits, constitutes an extremely powerful
alternative approach to quantum information processing. This review focuses on
continuous-variable quantum information processes that rely on any combination
of Gaussian states, Gaussian operations, and Gaussian measurements.
Interestingly, such a restriction to the Gaussian realm comes with various
benefits, since on the theoretical side, simple analytical tools are available
and, on the experimental side, optical components effecting Gaussian processes
are readily available in the laboratory. Yet, Gaussian quantum information
processing opens the way to a wide variety of tasks and applications, including
quantum communication, quantum cryptography, quantum computation, quantum
teleportation, and quantum state and channel discrimination. This review
reports on the state of the art in this field, ranging from the basic
theoretical tools and landmark experimental realizations to the most recent
successful developments.Comment: 51 pages, 7 figures, submitted to Reviews of Modern Physic
Quantum cryptography: key distribution and beyond
Uniquely among the sciences, quantum cryptography has driven both
foundational research as well as practical real-life applications. We review
the progress of quantum cryptography in the last decade, covering quantum key
distribution and other applications.Comment: It's a review on quantum cryptography and it is not restricted to QK
Continuous variable controlled quantum dialogue and secure multiparty quantum computation
A continuous variable controlled quantum dialogue scheme is proposed. The
scheme is further modified to obtain two other protocols of continuous variable
secure multiparty computation. The first one of these protocols provides a
solution of two party socialist millionaire problem, while the second protocol
provides a solution for a special type of multi-party socialist millionaire
problem which can be viewed as a protocol for multiparty quantum private
comparison. It is shown that the proposed scheme of continuous variable
controlled quantum dialogue can be performed using bipartite entanglement and
can be reduced to obtain several other two and three party cryptographic
schemes in the limiting cases. The security of the proposed scheme and its
advantage over corresponding discrete variable counterpart are also discussed.
Specifically, the ignorance of an eavesdropper in the proposed scheme is shown
to be very high compared with corresponding discrete variable scheme and thus
the present scheme is less prone to information leakage inherent with the
discrete variable quantum dialogue based schemes.It is further established that
the proposed scheme can be viewed as a continuous variable counterpart of
quantum cryptographic switch which allows a supervisor to control the
information transferred between the two legitimate parties to a continuously
varying degree.Comment: Quantum dialogue and its application in the continuous variable
scenario is studied in detai
Distributing Secret Keys with Quantum Continuous Variables: Principle, Security and Implementations
The ability to distribute secret keys between two parties with
information-theoretic security, that is, regardless of the capacities of a
malevolent eavesdropper, is one of the most celebrated results in the field of
quantum information processing and communication. Indeed, quantum key
distribution illustrates the power of encoding information on the quantum
properties of light and has far reaching implications in high-security
applications. Today, quantum key distribution systems operate in real-world
conditions and are commercially available. As with most quantum information
protocols, quantum key distribution was first designed for qubits, the
individual quanta of information. However, the use of quantum continuous
variables for this task presents important advantages with respect to qubit
based protocols, in particular from a practical point of view, since it allows
for simple implementations that require only standard telecommunication
technology. In this review article, we describe the principle of
continuous-variable quantum key distribution, focusing in particular on
protocols based on coherent states. We discuss the security of these protocols
and report on the state-of-the-art in experimental implementations, including
the issue of side-channel attacks. We conclude with promising perspectives in
this research field.Comment: 21 pages, 2 figures, 1 tabl
Trusted Noise in Continuous-Variable Quantum Key Distribution: a Threat and a Defense
We address the role of the phase-insensitive trusted preparation and
detection noise in the security of a continuous-variable quantum key
distribution, considering the Gaussian protocols on the basis of coherent and
squeezed states and studying them in the conditions of Gaussian lossy and noisy
channels. The influence of such a noise on the security of Gaussian quantum
cryptography can be crucial, even despite the fact that a noise is trusted, due
to a strongly nonlinear behavior of the quantum entropies involved in the
security analysis. We recapitulate the known effect of the preparation noise in
both direct and reverse-reconciliation protocols, as well as the detection
noise in the reverse-reconciliation scenario. As a new result, we show the
negative role of the trusted detection noise in the direct-reconciliation
scheme. We also describe the role of the trusted preparation or detection noise
added at the reference side of the protocols in improving the robustness of the
protocols to the channel noise, confirming the positive effect for the
coherent-state reverse-reconciliation protocol. Finally, we address the
combined effect of trusted noise added both in the source and the detector.Comment: 25 pages, 9 figure
Security of two-way quantum cryptography against asymmetric Gaussian attacks
Recently, we have shown the advantages of two-way quantum communications in
continuous variable quantum cryptography. Thanks to this new approach, two
honest users can achieve a non-trivial security enhancement as long as the
Gaussian interactions of an eavesdropper are independent and identical. In this
work, we consider asymmetric strategies where the Gaussian interactions can be
different and classically correlated. For several attacks of this kind, we
prove that the enhancement of security still holds when the two-way protocols
are used in direct reconciliation.Comment: Proceeding of the SPIE Conference "Quantum Communications and Quantum
Imaging VI" - San Diego 2008. This paper is connected with
arXiv:quant-ph/0611167 (for the last version see: Nature Physics 4, 726
(2008)
Continuous Variable Quantum Key Distribution with a Noisy Laser
Existing experimental implementations of continuous-variable quantum key
distribution require shot-noise limited operation, achieved with shot-noise
limited lasers. However, loosening this requirement on the laser source would
allow for cheaper, potentially integrated systems. Here, we implement a
theoretically proposed prepare-and-measure continuous-variable protocol and
experimentally demonstrate the robustness of it against preparation noise
stemming for instance from technical laser noise. Provided that direct
reconciliation techniques are used in the post-processing we show that for
small distances large amounts of preparation noise can be tolerated in contrast
to reverse reconciliation where the key rate quickly drops to zero. Our
experiment thereby demonstrates that quantum key distribution with
non-shot-noise limited laser diodes might be feasible.Comment: 10 pages, 6 figures. Corrected plots for reverse reconciliatio
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