955 research outputs found
Practical Decoy State for Quantum Key Distribution
Decoy states have recently been proposed as a useful method for substantially
improving the performance of quantum key distribution. Here, we present a
general theory of the decoy state protocol based on only two decoy states and
one signal state. We perform optimization on the choice of intensities of the
two decoy states and the signal state. Our result shows that a decoy state
protocol with only two types of decoy states--the vacuum and a weak decoy
state--asymptotically approaches the theoretical limit of the most general type
of decoy state protocols (with an infinite number of decoy states). We also
present a one-decoy-state protocol. Moreover, we provide estimations on the
effects of statistical fluctuations and suggest that, even for long distance
(larger than 100km) QKD, our two-decoy-state protocol can be implemented with
only a few hours of experimental data. In conclusion, decoy state quantum key
distribution is highly practical.Comment: 31 pages. 6 figures. Preprint forma
High-dimensional decoy-state quantum key distribution over 0.3 km of multicore telecommunication optical fibers
Multiplexing is a strategy to augment the transmission capacity of a
communication system. It consists of combining multiple signals over the same
data channel and it has been very successful in classical communications.
However, the use of enhanced channels has only reached limited practicality in
quantum communications (QC) as it requires the complex manipulation of quantum
systems of higher dimensions. Considerable effort is being made towards QC
using high-dimensional quantum systems encoded into the transverse momentum of
single photons but, so far, no approach has been proven to be fully compatible
with the existing telecommunication infrastructure. Here, we overcome such a
technological challenge and demonstrate a stable and secure high-dimensional
decoy-state quantum key distribution session over a 0.3 km long multicore
optical fiber. The high-dimensional quantum states are defined in terms of the
multiple core modes available for the photon transmission over the fiber, and
the decoy-state analysis demonstrates that our technique enables a positive
secret key generation rate up to 25 km of fiber propagation. Finally, we show
how our results build up towards a high-dimensional quantum network composed of
free-space and fiber based linksComment: Please see the complementary work arXiv:1610.01812 (2016
Decoy state quantum key distribution with two-way classical post-processing
Decoy states have recently been proposed as a useful method for substantially
improving the performance of quantum key distribution protocols when a coherent
state source is used. Previously, data post-processing schemes based on one-way
classical communications were considered for use with decoy states. In this
paper, we develop two data post-processing schemes for the decoy-state method
using two-way classical communications. Our numerical simulation (using
parameters from a specific QKD experiment as an example) results show that our
scheme is able to extend the maximal secure distance from 142km (using only
one-way classical communications with decoy states) to 181km. The second scheme
is able to achieve a 10% greater key generation rate in the whole regime of
distances
Security Analysis of an Untrusted Source for Quantum Key Distribution: Passive Approach
We present a passive approach to the security analysis of quantum key
distribution (QKD) with an untrusted source. A complete proof of its
unconditional security is also presented. This scheme has significant
advantages in real-life implementations as it does not require fast optical
switching or a quantum random number generator. The essential idea is to use a
beam splitter to split each input pulse. We show that we can characterize the
source using a cross-estimate technique without active routing of each pulse.
We have derived analytical expressions for the passive estimation scheme.
Moreover, using simulations, we have considered four real-life imperfections:
Additional loss introduced by the "plug & play" structure, inefficiency of the
intensity monitor, noise of the intensity monitor, and statistical fluctuation
introduced by finite data size. Our simulation results show that the passive
estimate of an untrusted source remains useful in practice, despite these four
imperfections. Also, we have performed preliminary experiments, confirming the
utility of our proposal in real-life applications. Our proposal makes it
possible to implement the "plug & play" QKD with the security guaranteed, while
keeping the implementation practical.Comment: 35 pages, 19 figures. Published Versio
Security of Plug-and-Play QKD Arrangements with Finite Resources
The security of a passive plug-and-play QKD arrangement in the case of finite
(resources) key lengths is analysed. It is assumed that the eavesdropper has
full access to the channel so an unknown and untrusted source is assumed. To
take into account the security of the BB84 protocol under collective attacks
within the framework of quantum adversaries, a full treatment provides the
well-known equations for the secure key rate. A numerical simulation keeping a
minimum number of initial parameters constant as the total error sought and the
number of pulses is carried out. The remaining parameters are optimized to
produce the maximum secure key rate. Two main strategies are addressed: with
and without two-decoy-states including the optimization of signal to decoy
relationship
Beating the PNS attack in practical quantum cryptography
In practical quantum key distribution, weak coherent state is often used and
the channel transmittance can be very small therefore the protocol could be
totally insecure under the photon-number-splitting attack. We propose an
efficient method to verify the upper bound of the fraction of counts caused by
multi-photon pluses transmitted from Alice to Bob, given whatever type of Eve's
action. The protocol simply uses two coherent states for the signal pulses and
vacuum for decoy pulse. Our verified upper bound is sufficiently tight for QKD
with very lossy channel, in both asymptotic case and non-asymptotic case. The
coherent states with mean photon number from 0.2 to 0.5 can be used in
practical quantum cryptography. We show that so far our protocol is the
decoy-state protocol that really works for currently existing set-ups.Comment: So far this is the unique decoy-state protocol which really works
efficiently in practice. Prior art results are commented in both main context
and the Appendi
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