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The standard way to measure the performance of existing continuous variable quantum key distribution (CVQKD) protocols is by using the achievable secret key rate (SKR) with respect to one parameter while keeping all other parameters constant. However, this atomistic method requires many individual parameter analyses while overlooking the co-dependence of other parameters. In this work, a numerical tool is developed for comparing different CVQKD protocols while taking into account the simultaneous effects of multiple CVQKD parameters on the capability of protocols to produce positive SKRs. Using the transmittance, excess noise, and modulation amplitude parameter space, regions of positive SKR are identified to compare three discrete modulated (DM) CVQKD protocols. The results show that the M-QAM protocol outperforms the M-APSK and M-PSK protocols and that there is a non-linear increase in the capability to produce positive SKRs as the number of coherent states used for a protocol increases. The tool developed is beneficial for choosing the optimum protocol in unstable channels, such as free space, where the transmittance and excess noise fluctuate, providing a more holistic assessment of a protocol's capability to produce positive SKRs. [ABSTRACT FROM AUTHOR]

Background: Body mass index (BMI) serves as a global metric for assessing obesity and overall health status. However, the impact of BMI, treated as a continuous variable, on the risk of perioperative stroke remains poorly understood. This retrospective cohort study aimed to elucidate the association between BMI and the risk of perioperative ischemic stroke in patients undergoing non‐cardiovascular surgery. Methods: A cohort of 223,415 patients undergoing noncardiac surgery at the First Medical Center of Chinese PLA General Hospital between January 1, 2008 and August 31, 2019 was screened. Preoperative high BMI, defined as BMI >22.64 kg/m2, was the primary exposure, and the outcome of interest was the new diagnosis of perioperative ischemic stroke within 30 days post‐surgery. Robust controls for patient and intraoperative factors were implemented to minimize residual confounding. Logistic regression and propensity score matching were employed, and patients were stratified into subgroups for further investigation. Results: The overall incidence of perioperative ischemic stroke was 0.23% (n = 525) in the cohort. After adjusting for patient‐related variables (OR 1.283; 95% CI, 1.04–1.594; p < 0.05), surgery‐related variables (OR 1.484; 95% CI, 1.2–1.849; p < 0.001), and all confounding variables (OR 1.279; 95% CI, 1.025–1.607; p < 0.05), patients with BMI >22.64 kg/m2 exhibited a significantly increased risk of perioperative ischemic stroke. This association persisted in the propensity score matched cohort (OR 1.577; 95% CI, 1.203–2.073; p < 0.01). Subgroup analyses indicated that preoperative BMI >22.64 kg/m2 correlated with an elevated risk of perioperative ischemic stroke in female patients, those with coronary heart disease, peripheral vascular diseases, and individuals undergoing neurosurgery. Conclusion: We first identified BMI >22.64 kg/m2 as a substantial and independent risk factor for perioperative ischemic stroke in Chinese noncardiac surgery patients. Normal BMI may not suffice as a universal preventive standard. Instead, a more stringent perioperative weight management approach is recommended, particularly for specific subgroups such as female patients, those with coronary heart disease and peripheral vascular disease, and individuals scheduled for neurosurgery. [ABSTRACT FROM AUTHOR]

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An entanglement-based continuous variable (CV) QKD scheme is proposed, performing information reconciliation over an entanglement-assisted link. The same entanglement generation source is used in both raw key transmission and information reconciliation. The entanglement generation source employs only low-cost devices operated in the C-band. The proposed CV-QKD scheme with information reconciliation over an entanglement-assisted link significantly outperforms the corresponding CV-QKD scheme with information reconciliation over an authenticated public channel. It also outperforms the CV-QKD scheme in which a classical free-space optical communication link is used to perform information reconciliation. An experimental demonstration over the free-space optical testbed established at the University of Arizona campus indicates that the proposed CV-QKD can operate in strong turbulence regimes. To improve the secret key rate performance further, adaptive optics is used. [ABSTRACT FROM AUTHOR]

We have introduced, for the first time, a protocol for Continuous-Variable Measurement-Device-Independent Quantum Key Distribution (CV-MDI-QKD) in the terahertz (THz) frequency band. We have conducted a secret key rate analysis against collective attacks. The proposed THz CV-MDI-QKD is immune to all detector attacks, significantly enhancing the security assurance of practical THz CVQKD implementations. Furthermore, we investigated the impact of finite key length (the finite-size effect) and finite reconciliation efficiency on the performance of practical THz CV-MDI-QKD systems. Our findings reveal that by employing a large number of keys or signals and optimizing the modulation variance, the detrimental effects arising from the finite-size effect and suboptimal reconciliation efficiency can be notably mitigated. These insights play a crucial role in advancing the feasibility of THz CVQKD technology towards practical applications. [ABSTRACT FROM AUTHOR]

Implementing quantum communication between space-separated local networks is essential for designing global quantum networks. In this study, we propose quantum teleportation and remote state preparation schemes between users of two space-separated local networks established by continuous-variable multipartite entangled states. In the proposed schemes, the quantum nodes belonging to the two distant local networks are first entangled by entanglement swapping, and then quantum communication protocols are realized. We show that quantum teleportation between any two users belonging to space-separated local networks can be realized with the assistance of other users, and squeezed thermal states can be remotely prepared in one local network by performing a homodyne projective measurement on the state in another distant local network. Our results provide a feasible approach for quantum communication between space-separated quantum networks with multipartite entangled states. [ABSTRACT FROM AUTHOR]

The standard way to measure the performance of existing continuous variable quantum key distribution (CVQKD) protocols is by using the achievable secret key rate (SKR) with respect to one parameter while keeping all other parameters constant. However, this atomistic method requires many individual parameter analyses while overlooking the co-dependence of other parameters. In this work, a numerical tool is developed for comparing different CVQKD protocols while taking into account the simultaneous effects of multiple CVQKD parameters on the capability of protocols to produce positive SKRs. Using the transmittance, excess noise, and modulation amplitude parameter space, regions of positive SKR are identified to compare three discrete modulated (DM) CVQKD protocols. The results show that the M-QAM protocol outperforms the M-APSK and M-PSK protocols and that there is a non-linear increase in the capability to produce positive SKRs as the number of coherent states used for a protocol increases. The tool developed is beneficial for choosing the optimum protocol in unstable channels, such as free space, where the transmittance and excess noise fluctuate, providing a more holistic assessment of a protocol’s capability to produce positive SKRs.

Distributed Constraint Optimization Problems (DCOPs) are an efficient framework widely used in multi-agent collaborative modeling. The traditional DCOP framework assumes that variables are discrete and constraint utilities are represented in tabular forms. However, the variables are continuous and constraint utilities are in functional forms in many practical applications. To overcome this limitation, researchers have proposed Continuous DCOPs (C-DCOPs), which can model DCOPs with continuous variables. However, most of the existing C-DCOP algorithms rely on gradient information for optimization, which means that they are unable to solve the situation where the utility function is a non-differentiable function. Although the Particle Swarm-Based C-DCOP (PCD) and Particle Swarm with Local Decision-Based C-DCOP (PCD-LD) algorithms can solve the situation with non-differentiable utility functions, they need to implement Breadth First Search (BFS) pseudo-trees for message passing. Unfortunately, employing the BFS pseudo-tree results in expensive computational overheads and agent privacy leakage, as messages are aggregated to the root node of the BFS pseudo-tree. Therefore, this paper aims to propose a fully distributed C-DCOP algorithm to solve the utility function form problem and avoid the disadvantages caused by the BFS pseudo-tree. Inspired by the population-based algorithms, we propose a fully decentralized local search algorithm, named Population-based Local Search Algorithm (PLSA), for solving C-DCOPs with three-fold advantages: (i) PLSA adopts a heuristic method to guide the local search to achieve a fast search for high-quality solutions; (ii) in contrast to the conventional C-DCOP algorithm, PLSA can solve utility functions of any form; and (iii) compared to PCD and PCD-LD, PLSA avoids complex message passing to achieve efficient computation and agent privacy protection. In addition, we implement an extended version of PLSA, named Population-based Global Search Algorithm (PGSA), and empirically show that our algorithms outperform the state-of-the-art C-DCOP algorithms on three types of benchmark problems. [ABSTRACT FROM AUTHOR]

Dual-polarization division multiplexing (DPDM) is considered to be a potential method to boost the secure key rate (SKR) of the continuous-variable quantum key distribution (CV-QKD) system. In this article, we propose a pilot alternately assisted local local oscillator (LLO) CV-QKD scheme based on multi-dimensional multiplexing, where time division multiplexing and frequency division multiplexing are combined with dual-polarization multiplexing techniques to dramatically isolate the quantum signal from the pilot tone. We establish a general excess noise model for the LLO CV-QKD system to analyze the influence mechanism of various disturbances (e.g., time-domain diffusion, frequency-domain modulation residual, and polarization perturbation) on the key parameters, such as the channel transmittance and excess noise. Specifically, the photon leakage noise from the reference path to the quantum path and that between quantum signals with two different polarization paths are simultaneously analyzed in the dual-polarization LLO CV-QKD scheme for the first time. Furthermore, a series of simulations are established to verify the performance of the proposed scheme. The results show that the maximal isolation degree achieves 84.0 dB~90.4 dB, and the crosstalk between pilot tones and quantum signals can be suppressed to a very small range. By optimizing the system parameters (e.g., modulation variance and repetition frequency), the SKR with 12.801 Mbps@25 km is achieved under the infinite polarization extinction ratio (PER) and 30 dB residual ratio of the frequency modulation in the nanosecond-level pulse width. Moreover, the performance of the proposed DPDM CV-QKD scheme under relatively harsh conditions is simulated; the results show that the SKR with 1.02 Mbps@25 km is achieved under a relatively low PER of 17 dB with the nanosecond-level pulse width and 20 dB residual ratio of the frequency modulation. Our work lays an important theoretical foundation for the practical DPDM LLO CV-QKD system. [ABSTRACT FROM AUTHOR]

Objective: In order to apply association rule mining to data sets with continuous variables, it is necessary to convert the variables into categorical structure. Therefore, we aim to compare the results obtained by categorizing continuous variables using different methods and analyzing them with association rule mining. Material and Methods: In this study, ChiMerge, clustering, Minimum Description Length Principle, equal interval, equal frequency methods were used to transform continuous variables into categorical structure by discretizing them. Various datasets were generated in the R with sample sizes of 100, 200, 500 and one binary dependent variable was created in each dataset. Additionally, 2, 3, 4, 5, 6, 7 continuous variables with a standard normal distribution were generated and various methods for transforming variables into categorical format were applied. A support of 10%, a confidence level of 80% were used. The number of rules varies based on the number of variables and the number of categories. Results: The study's results compared the descriptive statistics of the number of rules and the lift values. It can be said that high lift values are observed in scenarios with high levels of correlation and a higher number of variables and increasing the sample size can reduce the lift values of rules. Conclusion: In terms of the number of rules, the ChiMerge is the most affected by increasing the sample size. Furthermore, the ChiMerge yields stricter and higher lift values compared to other methods. While using association analysis, data type and multi-level associations should be considered. [ABSTRACT FROM AUTHOR]

Continuous-variable quantum key distribution offers simple, stable and easyto-implement key distribution systems. The discrete modulation scheme further reduces the technical difficulty. The main regret is that the security of discrete modulation schemes has not been sufficiently demonstrated. Schemes with different signal state distributions use various physical conditions to obtain the key rate formula, resulting in different security levels, computation complexities and implementation difficulties. Therefore, a relatively systematic and logically consistent security proof against most general attacks is worth exploring. On the other hand, extending the discrete modulation scheme and its variants to different applications, such as satellite-to-earth communication, can further activate and advance this field. Here, we briefly review the achievements that have been made in discretemodulated continuous-variable quantum key distribution, and openly discuss some issues worthy of further research. [ABSTRACT FROM AUTHOR]

Quantum Key Distribution (QKD) offers unconditional security in principle. Many QKD protocols have been proposed and demonstrated to ensure secure communication between two authenticated users. Continuous variable (CV) QKD offers many advantages over discrete variable (DV) QKD since it is cost-effective, compatible with current classical communication technologies, efficient even in daylight, and gives a higher secure key rate. Keeping this in view, we demonstrate a discrete modulated CVQKD protocol in the free space which is robust against polarization drift. We also present the simulation results with a noise model to account for the channel noise and the effects of various parameter changes on the secure key rate. These simulation results help us to verify the experimental values obtained for the implemented CVQKD.

The Bayesian network (BN) method has been successfully applied to evaluate earthquake liquefaction‐induced settlement of free‐field ground in recent years due to several specific advantages. However, the existing BN models need to discretize all continuous variables, and therefore, they can only predict the range value of the settlement (i.e., classification). Thus, information loss is inevitable in the process of discretization, which will largely reduce the prediction accuracy of the model. To realize the application of the BN method in the regression prediction of seismic liquefaction‐induced settlement, this study proposes a hybrid modelling method combining a hill‐climbing algorithm and domain knowledge to construct the structure of a continuous BN regression model based on historical liquefaction‐induced settlement data, and then the conditional linear Gaussian approach is used to learn the conditional probability distributions of parameters. A five‐fold cross‐validation test is used to demonstrate better generalization performance and advantages (such as considering model uncertainty and prior knowledge) of the continuous BN regression model compared with a discrete BN classification model, simplified methods such as the Tokimatsu & Seed and Ishihara & Yoshimine methods, and an artificial neural network model. Their advantages and disadvantages are discussed. In addition, the other two continuous BN models using the Arias intensity and cumulative absolute velocity instead of the peak ground acceleration perform slightly worse than the proposed continuous BN model, and the reason for this difference is discussed. [ABSTRACT FROM AUTHOR]

Abstract Background The multivariable fractional polynomial (MFP) approach combines variable selection using backward elimination with a function selection procedure (FSP) for fractional polynomial (FP) functions. It is a relatively simple approach which can be easily understood without advanced training in statistical modeling. For continuous variables, a closed test procedure is used to decide between no effect, linear, FP1, or FP2 functions. Influential points (IPs) and small sample sizes can both have a strong impact on a selected function and MFP model. Methods We used simulated data with six continuous and four categorical predictors to illustrate approaches which can help to identify IPs with an influence on function selection and the MFP model. Approaches use leave-one or two-out and two related techniques for a multivariable assessment. In eight subsamples, we also investigated the effects of sample size and model replicability, the latter by using three non-overlapping subsamples with the same sample size. For better illustration, a structured profile was used to provide an overview of all analyses conducted. Results The results showed that one or more IPs can drive the functions and models selected. In addition, with a small sample size, MFP was not able to detect some non-linear functions and the selected model differed substantially from the true underlying model. However, when the sample size was relatively large and regression diagnostics were carefully conducted, MFP selected functions or models that were similar to the underlying true model. Conclusions For smaller sample size, IPs and low power are important reasons that the MFP approach may not be able to identify underlying functional relationships for continuous variables and selected models might differ substantially from the true model. However, for larger sample sizes, a carefully conducted MFP analysis is often a suitable way to select a multivariable regression model which includes continuous variables. In such a case, MFP can be the preferred approach to derive a multivariable descriptive model.

We have introduced, for the first time, a protocol for Continuous-Variable Measurement-Device-Independent Quantum Key Distribution (CV-MDI-QKD) in the terahertz (THz) frequency band. We have conducted a secret key rate analysis against collective attacks. The proposed THz CV-MDI-QKD is immune to all detector attacks, significantly enhancing the security assurance of practical THz CVQKD implementations. Furthermore, we investigated the impact of finite key length (the finite-size effect) and finite reconciliation efficiency on the performance of practical THz CV-MDI-QKD systems. Our findings reveal that by employing a large number of keys or signals and optimizing the modulation variance, the detrimental effects arising from the finite-size effect and suboptimal reconciliation efficiency can be notably mitigated. These insights play a crucial role in advancing the feasibility of THz CVQKD technology towards practical applications.

An entanglement-based continuous variable (CV) QKD scheme is proposed, performing information reconciliation over an entanglement-assisted link. The same entanglement generation source is used in both raw key transmission and information reconciliation. The entanglement generation source employs only low-cost devices operated in the C-band. The proposed CV-QKD scheme with information reconciliation over an entanglement-assisted link significantly outperforms the corresponding CV-QKD scheme with information reconciliation over an authenticated public channel. It also outperforms the CV-QKD scheme in which a classical free-space optical communication link is used to perform information reconciliation. An experimental demonstration over the free-space optical testbed established at the University of Arizona campus indicates that the proposed CV-QKD can operate in strong turbulence regimes. To improve the secret key rate performance further, adaptive optics is used.

Quantum teleportation is one of the fundamental primitives of quantum cryptography. In order to achieve a wider range of high-capacity information transfer, we propose a free-space quantum teleportation (QT) protocol with orbital angular momentum (OAM) multiplexed continuous variable (CV) entangled states. The preparation of the entangled states is accomplished by the spontaneous four-wave mixing (SFWM) process occurring in a hot 85 Rb vapor cell, and the mode selection for the Bell-state measurement is achieved by employing the balanced homodyne detection technique. The fidelity of teleporting EPR entangled states carrying different topological charges via a Kolmogorov-type atmospheric turbulence channel is derived, and the superiority of enhancing the system channel capacity via OAM multiplexing is demonstrated. Our work provides a feasible scheme to implement high-capacity quantum communication in atmospheric environments. [ABSTRACT FROM AUTHOR]

Spatial modeling of ore grades is frequently impacted by the local variation in geological domains such as lithological characteristics, rock types, and geological formations. Disregarding this information may lead to biased results in the final ore grade block model, subsequently impacting the downstream processes in a mining chain project. In the current practice of ore body evaluation, which is known as stochastic cascade/hierarchical geostatistical modeling, the geological domain is first characterized, and then, within the geological model, the ore grades of interest are evaluated. This practice may be unrealistic in the case when the variability in ore grade across the boundary is gradual, following a smooth transition. To reproduce such characteristics, the cross dependence that exists between the ore grade and geological formations is considered in the conventional joint simulation between continuous and categorical variables. However, when using this approach, only one ore variable is considered, and its relationship with other ore grades that may be available at the sample location is ignored. In this study, an alternative approach to jointly model two cross-correlated ore grades and one categorical variable (i.e., geological domains) with soft contact relationships that exist among the geological domains is proposed. The statistical and geostatistical tools are provided for variogram inference, Gibbs sampling, and conditional cosimulation. The algorithm is also tested by applying it to a Cu deposit, where the geological formations are managed by the local and spatial distribution of two cross-correlated ore grades, Cu and Au, throughout the deposit. The results show that the proposed algorithm outperforms other geostatistical techniques in terms of global and local reproduction of statistical parameters. [ABSTRACT FROM AUTHOR]

Quantum satellite networking is central to enabling quantum key distribution (QKD) and quantum-state transfer. Delving into the synergistic relations of quantum technology and satellite communications, we elucidate on continuous variable and discrete variable QKD schemes, and the strategic selection of satellite orbits for optimal QKD. The prospects and possibilities of the integration of software-defined networking into this paradigm showcases a fusion of traditional and quantum communication methods. In the context of continuous variable quantum systems, a comparative discussion on Gaussian and non-Gaussian paradigms is presented, emphasizing their distinct characteristics crucial for satellite-assisted quantum networks. Moreover, we underscore the role of quantum computing in bolstering the security of satellite information networks, emphasizing the importance of delay reduction for the connection of Internet of Things (IoT) devices to satellite networks. Lastly, we propose potential domains ripe for future exploration in this burgeoning field.

Frequency entangled state originated from optical frequency comb (OFC) is an important quantum source for quantum communication. In this paper, we propose a traveling quantum anonymous voting (TQAV) protocol, which employs a monolithic microresonator with cascaded four-wave mixing (FWM) to prepare continuous-variable frequency entanglement sources. Multi-pair EPR entangled states and five-partite entangled states generated from the degenerate and nondegenerate FWM process are used as signal sources for the TQAV to characterize different candidates. Voters are able to vote for their preferred candidates by performing displacement operations on the received modes, and the ballot agency can judge the voting result according to the measurements. The entanglement property of the quantum state is utilized to keep voters away from the voting results. The security of the protocol under collective attacks and spectroscopic noise attacks is guaranteed by the security mechanism of continuous-variable quantum key distribution. Our results provide a reference for the application of OFC in multiparty quantum communication. [ABSTRACT FROM AUTHOR]

Quantum Key Distribution (QKD) is a cutting-edge communication method that enables secure communication between two parties. Continuous-variable QKD (CV-QKD) is a promising approach to QKD that has several advantages over traditional discrete-variable systems. Despite its potential, CV-QKD systems are highly sensitive to optical and electronic component impairments, which can significantly reduce the secret key rate. In this research, we address this challenge by modeling a CV-QKD system to simulate the impact of individual impairments on the secret key rate. The results show that laser frequency drifts and small imperfections in electro-optical devices such as the beam splitter and the balanced detector have a negative impact on the secret key rate. This provides valuable insights into strategies for optimizing the performance of CV-QKD systems and overcome limitations caused by component impairments. By offering a method to analyze them, the study enables the establishment of quality standards for the components of CV-QKD systems, driving the development of advanced technologies for secure communication in the future.

Distributed Constraint Optimization Problems (DCOPs) are an efficient framework widely used in multi-agent collaborative modeling. The traditional DCOP framework assumes that variables are discrete and constraint utilities are represented in tabular forms. However, the variables are continuous and constraint utilities are in functional forms in many practical applications. To overcome this limitation, researchers have proposed Continuous DCOPs (C-DCOPs), which can model DCOPs with continuous variables. However, most of the existing C-DCOP algorithms rely on gradient information for optimization, which means that they are unable to solve the situation where the utility function is a non-differentiable function. Although the Particle Swarm-Based C-DCOP (PCD) and Particle Swarm with Local Decision-Based C-DCOP (PCD-LD) algorithms can solve the situation with non-differentiable utility functions, they need to implement Breadth First Search (BFS) pseudo-trees for message passing. Unfortunately, employing the BFS pseudo-tree results in expensive computational overheads and agent privacy leakage, as messages are aggregated to the root node of the BFS pseudo-tree. Therefore, this paper aims to propose a fully distributed C-DCOP algorithm to solve the utility function form problem and avoid the disadvantages caused by the BFS pseudo-tree. Inspired by the population-based algorithms, we propose a fully decentralized local search algorithm, named Population-based Local Search Algorithm (PLSA), for solving C-DCOPs with three-fold advantages: (i) PLSA adopts a heuristic method to guide the local search to achieve a fast search for high-quality solutions; (ii) in contrast to the conventional C-DCOP algorithm, PLSA can solve utility functions of any form; and (iii) compared to PCD and PCD-LD, PLSA avoids complex message passing to achieve efficient computation and agent privacy protection. In addition, we implement an extended version of PLSA, named Population-based Global Search Algorithm (PGSA), and empirically show that our algorithms outperform the state-of-the-art C-DCOP algorithms on three types of benchmark problems.

Dual-polarization division multiplexing (DPDM) is considered to be a potential method to boost the secure key rate (SKR) of the continuous-variable quantum key distribution (CV-QKD) system. In this article, we propose a pilot alternately assisted local local oscillator (LLO) CV-QKD scheme based on multi-dimensional multiplexing, where time division multiplexing and frequency division multiplexing are combined with dual-polarization multiplexing techniques to dramatically isolate the quantum signal from the pilot tone. We establish a general excess noise model for the LLO CV-QKD system to analyze the influence mechanism of various disturbances (e.g., time-domain diffusion, frequency-domain modulation residual, and polarization perturbation) on the key parameters, such as the channel transmittance and excess noise. Specifically, the photon leakage noise from the reference path to the quantum path and that between quantum signals with two different polarization paths are simultaneously analyzed in the dual-polarization LLO CV-QKD scheme for the first time. Furthermore, a series of simulations are established to verify the performance of the proposed scheme. The results show that the maximal isolation degree achieves 84.0 dB~90.4 dB, and the crosstalk between pilot tones and quantum signals can be suppressed to a very small range. By optimizing the system parameters (e.g., modulation variance and repetition frequency), the SKR with 12.801 Mbps@25 km is achieved under the infinite polarization extinction ratio (PER) and 30 dB residual ratio of the frequency modulation in the nanosecond-level pulse width. Moreover, the performance of the proposed DPDM CV-QKD scheme under relatively harsh conditions is simulated; the results show that the SKR with 1.02 Mbps@25 km is achieved under a relatively low PER of 17 dB with the nanosecond-level pulse width and 20 dB residual ratio of the frequency modulation. Our work lays an important theoretical foundation for the practical DPDM LLO CV-QKD system.

In this paper, we present a neural network-based framework to compensate for the nonlinear distortion of high-speed continuous variable quantum key distribution (CV-QKD) systems. In practice, the nonlinear impairment of imperfect devices could bring interference to the measured quadrature values and thus compromise the parameter estimation procedure and the secure key rate. Specifically, for a high-speed CV-QKD system, the balanced homodyne detector (BHD) and the following analog-to-digital converter are the primary sources of nonlinear impairment. The nonlinear distortion effect will be more pronounced as the pulse repetition rate increases. We propose an autoencoder-based network to learn the inner patterns of distorted data and then compensate the quadrature measurements in real-time at the receiver’s side. The numerical simulation demonstrates that the excess noise induced by nonlinear impairment is reduced to the $10^{-3}$ level in the shot noise unit. Consequently, such a software approach has the ability to significantly boost the bandwidth efficiency of the BHD and the secure key bit rate.

Continuous-variable quantum key distribution offers simple, stable and easy-to-implement key distribution systems. The discrete modulation scheme further reduces the technical difficulty. The main regret is that the security of discrete modulation schemes has not been sufficiently demonstrated. Schemes with different signal state distributions use various physical conditions to obtain the key rate formula, resulting in different security levels, computation complexities and implementation difficulties. Therefore, a relatively systematic and logically consistent security proof against most general attacks is worth exploring. On the other hand, extending the discrete modulation scheme and its variants to different applications, such as satellite-to-earth communication, can further activate and advance this field. Here, we briefly review the achievements that have been made in discretemodulated continuous-variable quantum key distribution, and openly discuss some issues worthy of further research. [ABSTRACT FROM AUTHOR]

Quantum key distribution (QKD) is now moving toward a scalable and secure QKD network, which establishes secret keys among network users. The continuous-variable (CV) and discrete-variable (DV) QKD systems are currently being developed in parallel and are all used in QKD networks. We propose here a hybrid QKD network, in which the CV QKD system is used to build metropolitan QKD networks, and the DV QKD system is used to connect metropolitan QKD networks. The hybrid QKD network takes advantage of high secret key rates for CV QKD systems and long distance for DV QKD systems. We also present a feasible hybrid measurement-device-independent (MDI) QKD network, which combines both CV and DV MDI QKD systems. The presented hybrid QKD networks meet the low cost and compact requirement of a realistic QKD network and provide a feasible solution for future real QKD networks by combining the advantages of both CV and DV QKD systems. [ABSTRACT FROM AUTHOR]

Passive continuous variable quantum key distribution using multimode thermal source waives the necessity of usage of amplitude and phase modulators, thus it can effectively simplify the implementation of quantum key distribution. Compared with Gaussian modulation quantum key distribution scheme, this protocol is more cost-effective. However, the composable security of this scheme under collective attack has not been proved. In view of this, we take the composable security of the protocol under collective attack into consideration, and analyze the impact of the average photon number and mode-overlap coefficient on the performance of passive continuous variable quantum key distribution using multimode thermal source. In order to make comparison, we also calculate the asymptotic secret key rate of the passive continuous variable quantum key distribution protocol using multimode thermal source. Simulation results show that the composable secret key rate of this protocol is always lower than its asymptotic secret key rate. When the number of exchanged optical pulse signals is large enough, the composable secret key rate of the protocol approaches the asymptotic secret key rate. In addition, the composable secret key rate of this scheme can be further improved with the increase of average output photon number and mode-overlap coefficient. [ABSTRACT FROM AUTHOR]

Continuous-variable quantum teleportation (CVQT) plays a vital role in practical quantum communications. However, the degradation of quantum signals, usually caused by the absorption and scattering of light in actual scenarios, has an influence on the transmission performance and hence hinders its implementations. In this paper, we propose a non-Gaussian approach to improve the performance of CVQT via photon catalysis through a lossy optical fiber channel. The photon catalysis-enabled scheme can be performed on both sides of Einstein–Podolsky–Rosen state prepared by the receiver, where it gives birth to the enhancement of entanglement of the system. Numerical simulations show that the performance of the photon catalysis-enabled CVQT has been improved in terms of both fidelity and maximal transmission distance. Moreover, the larger the squeezing parameter results in the more enhancement of the CVQT system. The results may provide a useful insight for the practical implementation of CVQT. [ABSTRACT FROM AUTHOR]

Quantum teleportation is one of the fundamental primitives of quantum cryptography. In order to achieve a wider range of high-capacity information transfer, we propose a free-space quantum teleportation (QT) protocol with orbital angular momentum (OAM) multiplexed continuous variable (CV) entangled states. The preparation of the entangled states is accomplished by the spontaneous four-wave mixing (SFWM) process occurring in a hot 85Rb vapor cell, and the mode selection for the Bell-state measurement is achieved by employing the balanced homodyne detection technique. The fidelity of teleporting EPR entangled states carrying different topological charges via a Kolmogorov-type atmospheric turbulence channel is derived, and the superiority of enhancing the system channel capacity via OAM multiplexing is demonstrated. Our work provides a feasible scheme to implement high-capacity quantum communication in atmospheric environments.

Aiming at the high cost of quantum equipment and the difficulty of preparing discrete variable quantum states, a measurement-device-independent continuous variable semi-quantum key distribution (MDI-CV-SQKD) protocol is proposed. We, respectively, give the prepared-measure model and the entanglement-based (EB) model of the MDI-CV-SQKD protocol. Based on the EB model, we analyze the secret key rate and other performance of the protocol and perform numerical simulations. Then we analyze the amount of information transmitted by the channel under different attacks. As long as the channel parameters meet certain conditions, secure communication can be carried out. Through parameter adjustment, the solution can achieve the maximum secret key rate. The protocol has the advantages of easy preparation of continuous variables quantum states, low cost of semi-quantum user equipment, and high utilization of full quantum users. It also has characteristics such as the unconditional security of the full quantum protocol, the resistance to the detector side-channel attack of the measurement-device-independent protocol, and the extension of the transmission distance. Therefore, this protocol has important practical value. [ABSTRACT FROM AUTHOR]

The estimation of phase noise of continuous-variable quantum key distribution protocol with a local local oscillator (LLO CVQKD), as a major process in quantifying the secret key rate, is closely relevant to the intensity of the phase reference. However, the transmission of the phase reference through the insecure quantum channel is prone to be exploited by the eavesdropper (Eve) to mount attacks. Here, we introduce a polarization attack scheme against the phase reference. Presently, in a practical LLO CVQKD system, only part of the phase reference pulses are measured to compensate for the polarization drift of the quantum signal pulses in a compensation cycle due to the limited polarization measurement rate, while the other part of the phase reference pulses are not measured. We show that Eve can control the phase noise by manipulating the polarization direction of the unmeasured phase reference to hide her attack on the quantum signal. Simulations show that Eve can obtain partial or total key rates information shared between Alice and Bob as the transmission distance increases. Improving the polarization measurement rate to 100% or monitoring the phase reference intensity in real-time is of great importance to protect the LLO CVQKD from polarization attack. [ABSTRACT FROM AUTHOR]

In this paper, we present a neural network-based framework to compensate for the nonlinear distortion of high-speed continuous variable quantum key distribution (CV-QKD) systems. In practice, the nonlinear impairment of imperfect devices could bring interference to the measured quadrature values and thus compromise the parameter estimation procedure and the secure key rate. Specifically, for a high-speed CV-QKD system, the balanced homodyne detector (BHD) and the following analog-to-digital converter are the primary sources of nonlinear impairment. The nonlinear distortion effect will be more pronounced as the pulse repetition rate increases. We propose an autoencoder-based network to learn the inner patterns of distorted data and then compensate the quadrature measurements in real-time at the receiver’s side. The numerical simulation demonstrates that the excess noise induced by nonlinear impairment is reduced to the $10^{-3}$ level in the shot noise unit. Consequently, such a software approach has the ability to significantly boost the bandwidth efficiency of the BHD and the secure key bit rate. [ABSTRACT FROM AUTHOR]

Previous studies of causal learning heavily focused on binaryoutcomes; little is known about causal learning withcontinuous outcomes. The present paper proposes aqualitative extension of the causal power theory to thesituation where a binary cause influences a continuous effect,and induces causal power under various ceiling situationswith the continuous outcomes. To test the predictions, wesystematically manipulated the type of outcome (continuousvs. percentage vs. binary) and the contingency information.The experiment shows that people estimate causal strengthbased on the linear-sum rule for continuous outcomes and thenoisy-OR rule for binary outcomes. In the partial ceilingsituation where causal power is partially inferred but notprecisely estimated, the distribution of participants’judgments was bimodal with one mode at the minimum valueand the other at the maximum value, suggesting someparticipants made conservative estimates while others madeoptimistic estimates. These results are generally consistentwith the predictions of the causal power theory. Theoreticalimplications and future directions are discussed.

Secret sharing is a process in which a trusted party (the dealer) distributes a secret to several players who can only access the secret cooperatively. Here we propose a discrete modulation continuous variable quantum secret sharing (DM-CVQSS) protocol which utilizes the coherent states. In our protocol, the first player prepares a discrete modulation coherent state and sends it to the adjacent player who will manipulate the coherent state by the phase shift operation, and the other players do the same with the adjacent player. So our protocol allows the use of fewer devices to implement the QSS framework, and does not require every player to possess lasers and detectors. The performance of the protocol in the asymptotic scenario is analyzed by numerical simulation. In addition, by considering the finite-size effect, we can obtain a tighter DM-CVQSS distance bound, which is more practical than the asymptotic scenario. [ABSTRACT FROM AUTHOR]

We propose a continuous-variable quantum key distribution (CVQKD) scheme at terahertz (THz) bands based on multicarrier multiplexing (MCM) technology. In this scheme, multiple Gaussian modulated subcarriers are coupled to transmit multipath superposed thermal Gaussian states. At the receiver, optical discrete Fourier transform (ODFT) is used to demultiplex the received subcarriers, and the keys can be generated in parallel by homodyne detection and post processing. We analyze the security of the scheme against the optimal collective Gaussian attack under indoor environment and in inter-satellite links respectively. Results indicate that by using MCM technology, each subchannel may be affected by crosstalk, resulting in slight shortening of the maximal transmission distance while the total secret key rate can be greatly increased. We also verify the feasibility of higher key rate and longer distance THz-QKD by using MCM technology in inter-satellite links communication. We expect this work will provide an efficient path to build a global quantum communication network.

Mutual information is a popular metric in machine learning. In case of a discrete target variable and a continuous feature variable the mutual information can be calculated as a sum-integral of weighted log likelihood ratio of joint and marginal density distributions. However, in practice the true density distributions are unavailable and only a finite sample of the population is given. In this paper, we propose a novel method for calculating the mutual information for continuous variables using a finite sample of the population. The proposed method is based on approximating the underlying continuous density distribution using Kernel Density Estimation. Unlike previous kernel-based approaches for estimating mutual information, our method calculates directly the integral involved in the formula. Numerical experiments demonstrate that the proposed method produces more accurate results than the currently used feature selection approaches. In addition, our method demonstrates substantially faster computation times than the benchmark methods.

In this study, it was aimed to examine the probability problems which were posed based on continuous sample space and discrete sample space. Participants of the study consisted of 48 university students selected by using the convenience sampling method. Eight tasks related to continuous and discrete variables were designed by the researcher. Eight problems posed by each student in accordance with these tasks, their reflection papers and interviews conducted with them constituted the data of the study. Problems were analysed according to appropriateness, solvability, context, applicability, language and variable type dimensions. Findings revealed that most solvable problems were in real-life context, applicable and had clear language. However, most of the unsolvable problems had missing information. Inappropriate problems either were not generated depending on the task instructions or suitable variables were not used in them. Students had difficulties particularly in posing continuous sample space problems. It was concluded that problem posing was an effective practice for students since it enhanced their knowledge about probability and helped them to gain insight into problem posing. [ABSTRACT FROM AUTHOR]

Continuous-variable quantum key distribution (CV-QKD) over air quantum channel enables to provide unconditional information security, which is the one of most promising techniques for information wireless transfer. Since the air channel is of fluctuation in nature due to the presence of air turbulence, the random variations have to be taken into account when the security of CV-QKD is analyzed. We study the secret key rate of CV-QKD over the air quantum channel in this paper. The fluctuation of air channel is characterized by beam wandering and phase distortion under weak air turbulence conditions. The impact of fluctuation on the CV quantum signals is reflected by transmittance perturbation and phase shift. Our numerical results show that the secret key rate may keep relatively high level as the air quantum link increases at the outset. However, when the air link distance further increases beyond certain range, the secret key rate decreases strikingly since the both transmittance perturbation and the phase shift simultaneously deteriorate the performance of CV-QKD. Nevertheless, operating the CV-QKD under weak air turbulence conditions is available.

Many studies of causal judgments have dealt with the relationbetween the presence and the absence of a cause and an effect.However, little is known about causal learning with acontinuous outcome. The present study adopted Cohen’s d asan objective standard for effect size in situations where abinary cause influenced a continuous effect and investigatedhow people use means and standard deviations in theestimation of effect sizes. The experimental task was to read ascenario where the performance of two groups was comparedand to infer the causal effect. Whereas means weremanipulated while holding standard deviations constant in themean difference group, standard deviations were varied withholding means constant in the standard deviation differencegroup. The results demonstrate that participants could respondappropriately to the difference in two means, and that theygave a higher estimate of effect size in large standarddeviation situations than in small standard deviation situations.Judgments about standard deviations are in contrast toCohen’s d, indicating disproportionate attention to differentkinds of data samples.