Reconciliation Efficiency Research Articles

Enhancing discrete-modulated continuous-variable measurement-device-independent quantum key distribution via quantum catalysis

Discrete modulation can make up for the shortage of transmission distance in measurement-device-independent continuous-variable quantum key distribution (MDI-CVQKD), providing a unique advantage against all side-channel attacks but also creating a challenge for further performance improvement. Here we suggest a quantum catalysis (QC) approach for enhancing the performance of the discrete-modulated (DM) MDI-CVQKD in terms of the achievable secret key rate and lengthening the maximal transmission distance. The numerical simulation results show that the QC-based MDI-CVQKD with discrete modulation, involving a zero-photon catalysis (ZPC) operation, can not only obtain a higher secret key rate than the original DM protocol, but also contribute to a reasonable increase of the corresponding optimal variance. As for the extreme asymmetric and symmetric cases, the secret key rate and maximal transmission distance of the ZPC-involved DM MDI-CVQKD system can be further improved under the same parameters. This approach enables the system to tolerate lower reconciliation efficiency, which may provide excellent potential for practical implementations with state-of-art technology.

A Secure Communication Scheme Based on Equivalent Interference Channel Assisted by Physical Layer Secret Keys

Due to the channel estimation error, most of the physical layer secret key generation schemes need information reconciliation to correct error key bits, resulting in reduced efficiency. To solve the problem, this work proposes a novel secure communication scheme based on a equivalent interference channel. Different keys generated from imperfect channel state information are directly applied to signal scrambling and descrambling, which is equivalent to the process of a signal passing through an interference channel. Legitimate communication parties can reduce interference with the help of similar keys and channel coding without sending additional signals, while the eavesdropper channel is deteriorated due to the spatial decorrelation. For this kind of schemes, we first establish a discrete memoryless broadcast channel model to derive the expressions of bit error rate (BER), channel capacity, and security capacity for performance analysis. Simulation results verify the derivations that the proposed scheme achieves secure communication with a correlated eavesdropping channel and has a higher upper bound of transmission rate. Furthermore, we design a new metric to evaluate the efficiency and the result shows that the proposed scheme has superior performance on error reconciliation efficiency, despite its slight increase in BER.

High Efficiency Continuous-Variable Quantum Key Distribution Based on ATSC 3.0 LDPC Codes.

Due to the rapid development of quantum computing technology, encryption systems based on computational complexity are facing serious threats. Based on the fundamental theorem of quantum mechanics, continuous-variable quantum key distribution (CVQKD) has the property of physical absolute security and can effectively overcome the dependence of the current encryption system on the computational complexity. In this paper, we construct the spatially coupled (SC)-low-density parity-check (LDPC) codes and quasi-cyclic (QC)-LDPC codes by adopting the parity-check matrices of LDPC codes in the Advanced Television Systems Committee (ATSC) 3.0 standard as base matrices and introduce these codes for information reconciliation in the CVQKD system in order to improve the performance of reconciliation efficiency, and then make further improvements to final secret key rate and transmission distance. Simulation results show that the proposed LDPC codes can achieve reconciliation efficiency of higher than 0.96. Moreover, we can obtain a high final secret key rate and a long transmission distance through using our proposed LDPC codes for information reconciliation.

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 for practical systems to cope with the variable channel. Many researchers adopt fixed-rate error correction codes to implement adaptive reconciliation, such as the punctured LDPC code; however such protocol can achieve high efficiency only in a small range of signal-to-noise ratios (SNRs). In this paper, the spinal-based rateless reconciliation protocol for CV-QKD is first proposed. The proposed adaptive reconciliation protocol can achieve high efficiency in a much larger range of SNRs. Because the protocol we propose uses the code with short length and simple encoding/decoding structure, the design and implementation complexities of our protocol are greatly decreased. Meanwhile, its parallel attribute makes it suitable for hardware implementation, which means it has the potential of achieving high-throughput reconciliation. Moreover, the security of proposed protocol is investigated and proved. Experimental results show that the reconciliation efficiency of the spinal-based protocol maintains around $$95\%$$ in a larger SNR range (0,0.5), and even exceeds $$96.5\%$$ at extremely low SNR ( $$\le 0.032$$ ) with quite low frame error rate (FER) ( $$\le 5.2\%$$ ). Both the theoretical analysis and experimental results demonstrate that the proposed adaptive reconciliation protocol is a suitable candidate for the long-distance CV-QKD systems.

Comprehensive high-speed reconciliation for continuous-variable quantum key distribution

Reconciliation is currently the bottleneck of continuous-variable quantum key distribution systems for its great influence on the key rate and the distance of systems. In this paper, we address the increase in key rates by accelerating the speed of reconciliation algorithms based on the protocol of sliced error correction on a heterogeneous computing structure (a GPGPU card (general purpose graphics processing units will be abbreviated as GPU in this paper) and a general CPU) in the framework of Open Computing Language (OpenCL) (OpenCL is a programming framework based on C language). A block length of its component codes of low-density parity-check (LDPC) codes up to 2 $$^{17}$$ bits is employed in order to achieve a higher reconciliation efficiency. To meet the requirements of the OpenCL specifications, we designed a data structure, namely static cross bi-directional circular linked list, to store a super large sparse check matrix of the LDPC codes. Such a configuration ensures the practicability of our system, i.e. a better trade-off between the speed and net key rates of the reconciliation. The speed of the proposed reconciliation scheme reaches about 70.1 Mb/s with 512 codewords decoding in parallel, approximately 3600 times faster than that with the platform with only a CPU.

Phase-noise estimation using Bayesian inference for discretely modulated measurement-device-independent continuous-variable quantum key distribution

Measurement-device-independent continuous-variable quantum key distribution (MDI-CVQKD) protocol calibrates the phase reference frames by transmitting local oscillator pulses between two legitimate parties. The above implementation leaves massive loopholes; in particular, an eavesdropper can attack the system by manipulating the power of the local oscillator pulses. In this paper, a Bayesian phase-noise estimation model is proposed to estimate the phase drift and its uncertainty in the MDI-CVQKD protocol. The model employs the Bayesian estimation of the very weak quantum signal pulses and eliminates the necessity of transmitting local oscillator pulses between two legitimate parties. Moreover, the Bayesian inference algorithm has the characteristic of high robustness to noise and can achieve a well-motivated confidence interval of the estimated eigenphase. Comparing with its Gaussian counterpart, we adopt the discrete modulation in the MDI-CVQKD protocol, which allows a much better reconciliation efficiency at low signal-to-noise ratio. With simpler implementation, the proposed Bayesian phase-noise estimation model precisely avoids the security bottleneck due to the transmitted local oscillator pulses.

Multimatrix rate-compatible reconciliation for quantum key distribution

Key reconciliation of quantum key distribution (QKD) is the process of correcting errors caused by channel noise and eavesdropper to identify the keys of two legitimate users. Reconciliation efficiency is the most important figure for judging the quality of a reconciliation scheme. To improve reconciliation efficiency, rate-compatible technologies was proposed for key reconciliation, which is denoted as the single-matrix ratecompatible reconciliation (SRCR). In this paper, a recently suggested technique called multi-matrix reconciliation is introduced into SRCR, which is referred to as the multi-matrix rate-compatible reconciliation (MRCR), to further improve reconciliation efficiency and promote the throughput of SRCR. Simulation results show that MRCR we proposed outperforms SRCR in reconciliation efficiency and throughput.

Unidimensional Continuous-variable Quantum Key Distribution Based on Basis-encoding Coherent States Protocol

We propose the unidimensional continuous-variable quantum key distribution(UDCVQKD) protocol based on the basis-encoding of Gaussian modulated coherent states. the UDCVQKD protocol disregards the necessity in one of the quadrature modulations in coherent states. On that basis, we propose our scheme by encoding the secret keys on the either randomly selected measurement bases: the phase quadrature (X) or the amplitude quadrature (P), in order to slightly weaken the effects of reconciliation efficiency and channel excess noise compare to the present UCVQKD protocol. The new protocol with a view to simplify the precedent unidimensional protocols in the decoding procedure, meanwhile ensure the security of the quantum communication.

Free-space continuous-variable quantum key distribution in atmospheric channels based on low-density parity-check codes

Free-space continuous-variable quantum key distribution (CV-QKD) links provide greater information capability and broader geographical coverage. A major challenge for the practical use of free-space quantum systems is that the signal-to-noise ratios of the channels are relatively low and are sensitive to atmospheric disturbance. The atmospheric channel has several negative characteristics that diminish the secret key rate, such as beam extinction and various turbulence effects. The effect of beam wandering on the quantum properties is mainly considered, and the probability distribution of the transmission coefficient is derived to establish the channel model. Low-density parity-check (LDPC) codes operated in the reconciliation procedure are utilized to deal with information interactivity. However, the LDPC codes need to be chosen from a range of codes, where the code rate is considered in low signal-to-noise ratio free-space links. The accumulate–repeat–accumulate code is adopted to improve the decoding threshold of a code. It is found that the multi-edge feature of extended codes is beneficial to the performance of short- and medium-length codes. And numerical results show the proposed scheme provides enhancement in the reconciliation efficiency. LDPC codes containing an additional structure that facilitates decoding could be suitable for free-space CV-QKD protocols when weak atmospheric turbulence is considered.

Quantum catalysis-based discrete modulation continuous variable quantum key distribution with eight states

How to lengthen the maximum transmission of continuous variable quantum key distribution (CVQKD) has been a notorious hard problem in quantum communications. Here, we propose a simple solution to this problem, i.e., quantum catalyzing CVQKD for discrete modulation with eight states. The quantum catalysis, which can facilitate the conversion of the target ensemble, is used for not only tolerating more excess noise but also lengthening the maximum transmission distance. Security analysis shows that the zero-photon catalysis (ZPC), which is actually seen as a noiseless attenuation can be used as an elegant candidate for the performance improvement of discrete modulation (DM)-CVQKD. The numerical simulations show the ZPC-involved DM-CVQKD protocol outperforms the original DM-CVQKD in terms of maximum transmission distance as well as tolerable noise. Moreover, the ZPC-involved DM-CVQKD protocol can tolerate lower reconciliation efficiency and allow the lower detection efficiency to achieve the same performance.

Reconciliation for CV-QKD using globally-coupled LDPC codes**Project supported by the National Natural Science Foundation of China (Grant Nos. 61801522, 61972418, and 61872390), the Natural Science Foundation of Hunan Province, China (Grant Nos. 2019JJ40352 and 2017JJ3415), and the Special Foundation for Distinguished Young Scientists of Changsha City, China (Grant No. kq1905058).

Reconciliation is a necessary step in postprocessing of continuous-variable quantum key distribution (CV-QKD) system. We use globally coupled low-density parity-check (GC-LDPC) codes in reconciliation to extract a precise secret key from the raw keys over the authenticated classical public channel between two users. GC-LDPC codes have excellent performance over both the additive Gaussian white noise and binary-erasure channels. The reconciliation based on GC-LDPC codes can improve the reconciliation efficiency to 95.42% and reduce the frame error rate to 3.25 × 10–3. Using distillation, the decoding speed can achieve 23.8 Mbits/s and decrease the cost of memory. Given decoding speed and low memory usage, this makes the proposed reconciliation method viable approach for high-speed CV-QKD system.

Blind information reconciliation with variable step sizes for quantum key distribution

Quantum key distribution (QKD) generates symmetric keys between two authenticated parties with the guarantee of information-theoretically security. A vital step in QKD to obtain fully-matched key between two parties is information reconciliation. The blind reconciliation protocol provides a useful tool that corrects the mismatch in a wide range of qubit error rate (QBER) but without a prior error estimation. However, there is a contradiction between the reconciliation efficiency and the processing time in this protocol. In this work, we propose a blind reconciliation protocol with variable step sizes to relieve this contradiction. The analysis and simulation results show that the improved protocol inherits all the advantages of the original blind reconciliation protocol and can obtain better reconciliation efficiency with less operation time. The improved blind reconciliation protocol enhances the final secret key rate and accelerates the processing speed of a QKD system.

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.

Free-space continuous-variable quantum key distribution of unidimensional Gaussian modulation using polarized coherent states in an urban environment

We use single homodyne detector to accomplish Continuous-Variable quantum key distribution(CV QKD) in a laboratory and urban environment free-space channel. This is based on Gaussian modulation with coherent-states in the polarization degree of freedom. We achieved a QKD distance at 460m, at the repetition rate of 10 kHz. We give the security of this protocol against collective attack in the asymptotic regime. The secure key rate is 0.152 kbps at the typical reconciliation efficiency of 0.95. The experiment setup of this scheme is simplified and the difficulty to realize has been remarkably reduced compared to traditional symmetric modulation ones, for example, GG02 protocol. The influence of security key rate brought by asymmetric modulation is small in a relative low channel loss condition in the free-space environment. This scheme is expected to be significance meaning to the future practically utilize.

A Hybrid Information Reconciliation Method for Physical Layer Key Generation.

Physical layer key generation (PKG) has become a research focus as it solves the key distribution problem, which is difficult in traditional cryptographic mechanisms. Information reconciliation is a critical process in PKG to obtain symmetric keys. Various reconciliation schemes have been proposed, including the error detection protocol-based approach (EDPA) and error correction code-based approach (ECCA). Both EDPA and ECCA have advantages and drawbacks, regarding information leakage, interaction delay, and computation complexity. In this paper, we choose the BBBSS protocol from EDPA and BCH code from ECCA as a case study, analyzing their comprehensive efficiency performance versus pass number and bit disagreement ratio (BDR), respectively. Next, we integrate the strength of the two to design a new hybrid information reconciliation protocol (HIRP). The design of HIRP consists of three main phases, i.e., training, table lookup, and testing. To comprehensively evaluate the reconciliation schemes, we propose a novel efficiency metric to achieve a balance of corrected bits, information leakage, time delay, and computation time, which represents the effectively corrected bits per unit time. The simulation results show that our proposed method outperforms other reconciliation schemes to improve the comprehensive reconciliation efficiency. The average improvement in efficiency is 2.48 and 22.36 times over the BBBSS and BCH code, respectively, when the range of the BDR is from 0.5% to 11.5%. Compared to the BBBSS protocol and the BCH code, HIRP lies at a mid-level in terms of information leakage and computation time cost. Besides, with the lowest time delay cost, HIRP reaches the highest reconciliation efficiency.

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%.

Continuous-variable QKD over 50 km 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 by employing an efficient calibration model with one-time evaluation. This accomplishment is also realized by developing a fully automatic control system which stabilizes system noise, and by applying a rate-adaptive reconciliation method which maintains high reconciliation efficiency with high success probability in fluctuated environments. Our results pave the way for the deployment of continuous-variable QKD in metropolitan settings.

Multi-matrix error estimation and reconciliation for quantum key distribution.

Post-processing is a significant step in quantum key distribution (QKD), which is used for correcting the quantum-channel noise errors and distilling identical corrected keys between two distant legitimate parties. Efficient error reconciliation protocol, which can lead to an increase in the secure key generation rate, is one of the main performance indicators of QKD setups. In this paper, we propose a multi-low-density parity-check codes based reconciliation scheme, which can provide remarkable perspectives for highly efficient information reconciliation. By testing our approach through data simulation, we show that the proposed scheme combining multi-syndrome-based error rate estimation allows for a more accurate estimation of the error rate as compared with random sampling and single-syndrome estimation techniques before the error correction, as well as a significant increase in the efficiency of the procedure without compromising security and sacrificing reconciliation efficiency.

Realistic rate-distance limit of continuous-variable quantum key distribution.

Continuous variable quantum key distribution (CV QKD) is a promising candidate for the deployment of quantum cryptography. At present, the longest distance is limited to ∼100 km at fiber-based quantum channel. We investigated in depth the realistic rate-distance limit (RDL) of CV QKD, considering reconciliation efficiency, finite-size effect, and realistic excess noise under collective attack. It is shown that the excess noise generated on Bob's side degrades significantly the transmission distance and we verify it in experiment. The improvement in RDL by reconciliation efficiency depends on the excess noise level, considerable increase of RDL by improving the reconciliation efficiency occurs only for relative large excess noises. A convergence modulation variance, useful in calculation simplification, is found. Furthermore, we restudy the finite-size analysis and eliminates a loophole arising from the Holevo-bound information monotonicity and a safe RDL is guaranteed. Based on the revised finite-size analysis, the optimum ratio determining the amount of data used for parameter estimation is analyzed.

Pharmacists and medication reconciliation: a review of recent literature.

Background: Adverse drug event (ADE) errors are common and costly in health care systems across the world. Medication reconciliation is a means to decrease these medication-related injuries and increase quality of care. Research has shown that medication reconciliation accuracy and efficiency improved when pharmacists are directly involved in the process.Objective: We review studies examining how pharmacists impact the medication reconciliation process and we discuss pharmacists’ future roles during the medication reconciliation process and then barriers pharmacy staff may face during this critical process.Methods: A comprehensive literature search from MEDLINE and manual searching of bibliographies was performed for the time period January 2012 through November 2018.Conclusion: Although the issue of rising costs and injury due to medication errors in our health care system are not solvable via medication reconciliation alone, it is the first and perhaps most critical piece of the medication management puzzle. As such, numerous organizations have called for pharmacists to expand their roles in the medication reconciliation process due to their expertise in medication management.