105,588 research outputs found
One-way Quantum Key Distribution System based on Planar Lightwave Circuits
We developed a one-way quantum key distribution (QKD) system based upon a
planar lightwave circuit (PLC) interferometer. This interferometer is expected
to be free from the backscattering inherent in commercially available two-way
QKD systems and phase drift without active compensation. A key distribution
experiment with spools of standard telecom fiber showed that the bit error rate
was as low as 6% for a 100-km key distribution using an attenuated laser pulse
with a mean photon number of 0.1 and was determined solely by the detector
noise. This clearly demonstrates the advantages of our PLC-based one-way QKD
system over two-way QKD systems for long distance key distribution.Comment: 23 pages, 5 figure
Which verification qubits perform best for secure communication in noisy channel?
In secure quantum communication protocols, a set of single qubits prepared
using 2 or more mutually unbiased bases or a set of -qubit ()
entangled states of a particular form are usually used to form a verification
string which is subsequently used to detect traces of eavesdropping. The qubits
that form a verification string are referred to as decoy qubits, and there
exists a large set of different quantum states that can be used as decoy
qubits. In the absence of noise, any choice of decoy qubits provides equivalent
security. In this paper, we examine such equivalence for noisy environment
(e.g., in amplitude damping, phase damping, collective dephasing and collective
rotation noise channels) by comparing the decoy-qubit assisted schemes of
secure quantum communication that use single qubit states as decoy qubits with
the schemes that use entangled states as decoy qubits. Our study reveals that
the single qubit assisted scheme perform better in some noisy environments,
while some entangled qubits assisted schemes perform better in other noisy
environments. Specifically, single qubits assisted schemes perform better in
amplitude damping and phase damping noisy channels, whereas a few
Bell-state-based decoy schemes are found to perform better in the presence of
the collective noise. Thus, if the kind of noise present in a communication
channel (i.e., the characteristics of the channel) is known or measured, then
the present study can provide the best choice of decoy qubits required for
implementation of schemes of secure quantum communication through that channel.Comment: 11 pages, 4 figure
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
Experimental quantum key distribution based on a Bell test
We report on a complete free-space field implementation of a modified Ekert91
protocol for quantum key distribution using entangled photon pairs. For each
photon pair we perform a random choice between key generation and a Bell
inequality. The amount of violation is used to determine the possible knowledge
of an eavesdropper to ensure security of the distributed final key.Comment: 5 pages ReVTeX, 3 figures; version v2 with updated references and
minor corrections, author spelling fixe
- …