77 research outputs found
Efficient rate-adaptive reconciliation for continuous-variable quantum key distribution
Information reconciliation protocol has a significant effect on the secret
key rate and maximal transmission distance of continuous-variable quantum key
distribution (CV-QKD) systems. We propose an efficient rate-adaptive
reconciliation protocol suitable for practical CV-QKD systems with time-varying
quantum channel. This protocol changes the code rate of multi-edge type low
density parity check codes, by puncturing (increasing the code rate) and
shortening (decreasing the code rate) techniques, to enlarge the correctable
signal-to-noise ratios regime, thus improves the overall reconciliation
efficiency comparing to the original fixed rate reconciliation protocol. We
verify our rate-adaptive reconciliation protocol with three typical code rate,
i.e., 0.1, 0.05 and 0.02, the reconciliation efficiency keep around 93.5%,
95.4% and 96.4% for different signal-to-noise ratios, which shows the potential
of implementing high-performance CV-QKD systems using single code rate matrix.Comment: 12 pages, 5 figure
Continuous-variable QKD over 50km commercial fiber
The continuous-variable version of quantum key distribution (QKD) offers the
advantages (over discrete-variable systems) of higher secret key rates in
metropolitan areas as well as the use of standard telecom components that can
operate at room temperature. An important step in the real-world adoption of
continuous-variable QKD is the deployment of field tests over commercial
fibers. Here we report two different field tests of a continuous-variable QKD
system through commercial fiber networks in Xi'an and Guangzhou over distances
of 30.02 km (12.48 dB) and 49.85 km (11.62 dB), respectively. We achieve secure
key rates two orders-of-magnitude higher than previous field test
demonstrations. This is achieved by developing a fully automatic control system
to create stable excess noise and by applying a rate-adaptive reconciliation
protocol to achieve a high reconciliation efficiency with high success
probability. Our results pave the way to achieving continuous-variable QKD in a
metropolitan setting.Comment: 19 pages, 6 figure
Satellite-Based Continuous-Variable Quantum Communications: State-of-the-Art and a Predictive Outlook
The recent launch of the Micius quantum-enabled satellite heralds a major
step forward for long-range quantum communication. Using single-photon
discrete-variable quantum states, this exciting new development proves beyond
any doubt that all of the quantum protocols previously deployed over limited
ranges in terrestrial experiments can, in fact, be translated to global
distances via the use of low-orbit satellites. In this work, we survey the
imminent extension of space-based quantum communication to the
continuous-variable regime - the quantum regime perhaps most closely related to
classical wireless communications. The CV regime offers the potential for
increased communication performance and represents the next major step forward
for quantum communications and the development of the global quantum internet.Comment: Submitted to IEEE Communications Surveys and Tutorials. Contains
updated reference
Information Reconciliation for Continuous-Variable Quantum Key Distribution using Non-Binary Low-Density Parity-Check Codes
An information reconciliation method for continuous-variable quantum key
distribution with Gaussian modulation that is based on non-binary low-density
parity-check (LDPC) codes is presented. Sets of regular and irregular LDPC
codes with different code rates over the Galois fields , ,
, and have been constructed. We have performed simulations to
analyze the efficiency and the frame error rate using the sum-product
algorithm. The proposed method achieves an efficiency between and
if the signal-to-noise ratio is between dB and dB.Comment: 23 pages, 7 figure
High speed error correction for continuous-variable quantum key distribution with multi-edge type LDPC code
Error correction is a significant step in postprocessing of
continuous-variable quantum key distribution system, which is used to make two
distant legitimate parties share identical corrected keys. We propose an
experiment demonstration of high speed error correction with multi-edge type
low-density parity check (MET-LDPC) codes based on graphic processing unit
(GPU). GPU supports to calculate the messages of MET-LDPC codes simultaneously
and decode multiple codewords in parallel. We optimize the memory structure of
parity check matrix and the belief propagation decoding algorithm to reduce
computational complexity. Our results show that GPU-based decoding algorithm
greatly improves the error correction speed. For the three typical code rate,
i.e., 0.1, 0.05 and 0.02, when the block length is and the iteration
number are 100, 150 and 200, the average error correction speed can be
respectively achieved to 30.39Mbits/s (over three times faster than previous
demonstrations), 21.23Mbits/s and 16.41Mbits/s with 64 codewords decoding in
parallel, which supports high-speed real-time continuous-variable quantum key
distribution system.Comment: 8 pages, 2 figure
High Throughput and Low Cost LDPC Reconciliation for Quantum Key Distribution
Reconciliation is a crucial procedure in post-processing of Quantum Key
Distribution (QKD), which is used for correcting the error bits in sifted key
strings. Although most studies about reconciliation of QKD focus on how to
improve the efficiency, throughput optimizations have become the highlight in
high-speed QKD systems. Many researchers adpot high cost GPU implementations to
improve the throughput. In this paper, an alternative high throughput and
efficiency solution implemented in low cost CPU is proposed. The main
contribution of the research is the design of a quantized LDPC decoder
including improved RCBP-based check node processing and saturation-oriented
variable node processing. Experiment results show that the throughput up to
60Mbps is achieved using the bi-directional approach with reconciliation
efficiency approaching to 1.1, which is the optimal combination of throughput
and efficiency in Discrete-Variable QKD (DV-QKD). Meanwhile, the performance
remains stable when Quantum Bit Error Rate (QBER) varies from 1% to 8%
Adding artificial noise for code rate matching in continuous-variable quantum key distribution
The reconciliation step of continuous-variable quantum key distribution
protocols usually involves forward error correction codes. Matching the code
rate and the signal-to-noise ratio (SNR) of the quantum channel is required to
achieve the high reconciliation efficiencies that are crucial for long distance
links. Puncturing and shortening is a way to adapt the code rate to the SNR at
the cost of a slightly reduced reconciliation efficiencies. Instead of adapting
the code rate to the SNR, we propose to add a controlled amount of artificial
noise to the measured data, so that the resulting SNR could be reduced to match
the given code rate. We show that our method can compete with puncturing and
shortening and even outperform it in high-loss, high-excess noise scenarios
Novel Reconciliation Protocol Based on Spinal Code for Continuous-variable Quantum Key Distribution
Reconciliation is a crucial procedure in post-processing of continuous
variable quantum key distribution (CV-QKD) system, which is used to make two
distant legitimate parties share identical corrected keys. The adaptive
reconciliation is necessary and important for practical systems to cope with
the variable channel. Many researchers adopt the punctured LDPC codes to
implement adaptive reconciliation. In this paper, a novel rateless
reconciliation protocol based on spinal code is proposed, which can achieve a
high-efficiency and adaptive reconciliation in a larger range of SNRs. Due to
the short codes length and simple tructure, our protocol is easy to implement
without the complex codes designs of fixed rate codes, e.g., LDPC codes.
Meanwhile, the structure of our protocol is highly parallel, which is suitable
for hardware implementation, thus it also has the potential of high-speed
hardware implementation. Besides, the security of proposed protocol is proved
in theory. Experiment results show that the reconciliation efficiency maintains
around 95% for ranging SNRs in a larger range (0,0.5), even exceeds 96.5% at
extremely low SNR (<= 0.03) by using this novel scheme. The proposed protocol
makes the long-distance CV-QKD systems much easier and stable to perform a
high-performance and adaptive reconciliation
Feasibility Assessment For Practical Continuous Variable Quantum Key Distribution Over The Satellite-to-Earth Channel
Currently, quantum key distribution (QKD) using continuous variable (CV)
technology has only been demonstrated over short-range terrestrial links. Here
we attempt to answer whether CV-QKD over the much longer satellite-to-Earth
channel is feasible. To this end, we first review the concepts and technologies
that will enable CV-QKD over the satellite-to-Earth channels. We then consider,
in the infinite key limit, the simplest-to-deploy QKD protocols, the coherent
state (CS) QKD protocol with homodyne detection and the CS-QKD protocol with
heterodyne detection. We then focus on the CS-QKD protocol with heterodyne
detection in the pragmatic setting of finite keys, where complete security
against general attacks is known. We pay particular attention to the relevant
noise terms in the satellite-to-Earth channel and their impact on the secret
key rates. In system set-ups where diffraction dominates losses, we find that
the main components of the total excess noise are the intensity fluctuations
due to scintillation, and the time-of-arrival fluctuations between signal and
local oscillator. We conclude that for a wide range of pragmatic system models,
CS-QKD with information-theoretic security in the satellite-to-Earth channel is
feasible.Comment: 16 pages, 6 figures, 4 tables, Closest to Published Versio
Continuous-Variable Quantum Key Distribution with Rateless Reconciliation Protocol
Information reconciliation is crucial for continuous-variable quantum key
distribution (CV-QKD) because its performance affects the secret key rate and
maximal secure transmission distance. Fixed-rate error correction codes limit
the potential applications of the CV-QKD because of the difficulty of
optimizing such codes for different low SNRs. In this paper, we propose a
rateless reconciliation protocol combined multidimensional scheme with Raptor
codes that not only maintains the rateless property but also achieves high
efficiency in different SNRs using just one degree distribution. It
significantly decreases the complexity of optimization and increases the
robustness of the system. Using this protocol, the CV-QKD system can operate
with the optimal modulation variance which maximizes the secret key rate.
Simulation results show that the proposed protocol can achieve reconciliation
efficiency of more than 95% within the range of SNR from -20 dB to 0 dB. It
also shows that we can obtain a high secret key rate at arbitrary distances in
a certain range and achieve a secret key rate of about 5*10^(-4) bits/pulse at
a maximum distance of 132 km (corresponding SNR is -20dB) that is higher than
previous works. The proposed protocol can maintain high efficient key
extraction under the wide range of SNRs and paves the way toward the practical
application of CV-QKD systems in flexible scenarios.Comment: 10 pages, 6 figure
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