341 research outputs found
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
Unidimensional continuous-variable quantum key distribution
We propose the continuous-variable quantum key distribution protocol based on
the Gaussian modulation of a single quadrature of the coherent states of light,
which is aimed to provide simplified implementation compared to the
symmetrically modulated Gaussian coherent-state protocols. The protocol waives
the necessity in phase quadrature modulation and the corresponding channel
transmittance estimation. The security of the protocol against collective
attacks in a generally phase-sensitive Gaussian channels is analyzed and is
shown achievable upon certain conditions. Robustness of the protocol to channel
imperfections is compared to that of the symmetrical coherent-state protocol.
The simplified unidimensional protocol is shown possible at a reasonable
quantitative cost in terms of key rate and of tolerable channel excess noise.Comment: 7 pages, 5 figures, close to the published versio
Complete elimination of information leakage in continuous-variable quantum communication channels
In all lossy communication channels realized to date, information is
inevitably leaked to a potential eavesdropper. Here we present a communication
protocol that does not allow for any information leakage to a potential
eavesdropper in a purely lossy channel. By encoding information into a
restricted Gaussian alphabet of squeezed states we show, both theoretically and
experimentally, that the Holevo information between the eavesdropper and the
intended recipient can be exactly zero in a purely lossy channel while
minimized in a noisy channel. This result is of fundamental interest, but might
also have practical implications in extending the distance of secure quantum
key distribution.Comment: 9 pages, 5 figure
Single-Quadrature Continuous-Variable Quantum Key Distribution
Most continuous-variable quantum key distribution schemes are based on the
Gaussian modulation of coherent states followed by continuous quadrature
detection using homodyne detectors. In all previous schemes, the Gaussian
modulation has been carried out in conjugate quadratures thus requiring two
independent modulators for their implementations. Here, we propose and
experimentally test a largely simplified scheme in which the Gaussian
modulation is performed in a single quadrature. The scheme is shown to be
asymptotically secure against collective attacks, and considers asymmetric
preparation and excess noise. A single-quadrature modulation approach renders
the need for a costly amplitude modulator unnecessary, and thus facilitates
commercialization of continuous-variable quantum key distribution.Comment: 13 pages, 7 figure
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
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