871 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
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
Finding and breaking the realistic rate-distance limit of continuous variable quantum key distribution
In this work, the rate-distance limit of continuous variable quantum key
distribution is studied. We find that the excess noise generated on Bob's side
and the method for calculating the excess noise restrict the rate-distance
limit. Then, a realistic rate-distance limit is found. To break the realistic
limit, a method for calculating the secret key rate using pure excess noise is
proposed. The improvement in the rate-distance limit due to a higher
reconciliation efficiency is analyzed. It is found that this improvement is
dependent on the excess noise. From a finite-size analysis, the monotonicity of
the Holevo bound versus the transmission efficiency is studied, and a tighter
rate-distance limit is presented.Comment: 5 pages,5 figure
- …