Information reconciliation is a significant step for a continuous-variable quantum key distribution（CV-QKD） system.We propose a reconciliation method that allows two authorized parties to extract a consistent and se...Information reconciliation is a significant step for a continuous-variable quantum key distribution（CV-QKD） system.We propose a reconciliation method that allows two authorized parties to extract a consistent and secure binary key in a CV-QKD protocol,which is based on Gaussian-modulated coherent states and homodyne detection.This method named spherical reconciliation is based on spherical quantization and non-binary low-density parity-check（LDPC） codes.With the suitable signal-to-noise ratio（SNR） and code rate of non-binary LDPC codes,spherical reconciliation algorithm has a high efficiency and can extend the transmission distance of CV-QKD.展开更多
Considering the ocean water＇s optical attenuation and the roughness of the sea surface, we analyze the security of continuous-variable （CV） quantum key distribution （QKD） based Mr-to-water channel. The effects of...Considering the ocean water＇s optical attenuation and the roughness of the sea surface, we analyze the security of continuous-variable （CV） quantum key distribution （QKD） based Mr-to-water channel. The effects of the absorp- tion and scattering on the transmittance of underwater quantum channel and the maximum secure transmission distance are studied. Considering the roughness of the sea surface, we simulate the performance bounds of CV QKD with different wind speeds using the Monte Carlo method. The results show that even if the secret key rate gradually reduces as the wind speed increases, the maximum transmission distance will not be affected obviously. Compared to the works regarding short-distance underwater optical communication, our research represents a significant step towards establishing secure communication between air platform and submarine vehicle.展开更多
Gaussian-modulated coherent state quantum key distribution is gradually moving towards practical application. Generally, the involved scheme is based on the binary random basis choice. To improve the performance and s...Gaussian-modulated coherent state quantum key distribution is gradually moving towards practical application. Generally, the involved scheme is based on the binary random basis choice. To improve the performance and security, we present a scheme based on a continuous random basis choice. The results show that our scheme obviously improves the performance, such as the secure communication distance. Our scheme avoids comparing the measurement basis and discarding the key bits, and it can be easily implemented with current technology. Moreover, the imperfection of the basis choice can be well removed by the known phase compensation algorithm.展开更多
The trans-media transmission of quantum pulse is one of means of free-space transmission which can be applied in continuous-variable quantum key distribution(CVQKD)system.In traditional implementations for atmospheric...The trans-media transmission of quantum pulse is one of means of free-space transmission which can be applied in continuous-variable quantum key distribution(CVQKD)system.In traditional implementations for atmospheric channels,the 1500-to-1600-nm pulse is regarded as an ideal quantum pulse carrier.However,the underwater transmission of this pulses tends to suffer from severe attenuation,which inevitably deteriorates the security of the whole CVQKD system.In this paper,we propose an alternative scheme for implementations of CVQKD over satellite-to-submarine channels.We estimate the parameters of the trans-media channels,involving atmosphere,sea surface and seawater and find that the shortwave infrared performs well in the above channels.The 450-nm pulse is used for generations of quantum signal carriers to accomplish quantum communications through atmosphere,sea surface and seawater channels.Numerical simulations show that the proposed scheme can achieve the transmission distance of 600 km.In addition,we demonstrate that non-Gaussian operations can further lengthen its maximal transmission distance,which contributes to the establishment of practical global quantum networks.展开更多
We propose a method to improve the secret key rate of an eight-state continuous-variable quantum key distribution（CVQKD） by using a linear optics cloning machine（LOCM）. In the proposed scheme, an LOCM is exploited...We propose a method to improve the secret key rate of an eight-state continuous-variable quantum key distribution（CVQKD） by using a linear optics cloning machine（LOCM）. In the proposed scheme, an LOCM is exploited to compensate for the imperfections of Bob＇s apparatus, so that the generated secret key rate of the eight-state protocol could be well enhanced. We investigate the security of our proposed protocol in a finite-size scenario so as to further approach the practical value of a secret key rate. Numeric simulation shows that the LOCM with reasonable tuning gain λ and transmittance τcan effectively improve the secret key rate of eight-state CVQKD in both an asymptotic limit and a finite-size regime.Furthermore, we obtain the tightest bound of the secure distance by taking the finite-size effect into account, which is more practical than that obtained in the asymptotic limit.展开更多
The well-known multi-dimensional reconciliation is an effective method used in the continuous-variable quantum key distribution in the long-distance and the low signal-to-noise-ratio scenarios.The virtual channel empl...The well-known multi-dimensional reconciliation is an effective method used in the continuous-variable quantum key distribution in the long-distance and the low signal-to-noise-ratio scenarios.The virtual channel employed to exchange data is generally established by using a finite-dimensional rotation in the reconciliation procedure.In this paper,we found that the finite dimension of the multi-dimensional reconciliation inevitably leads to the mismatch of the signal-to-noise-ratio between the quantum channel and the virtual channel,which may be called the finite-dimension effect.Such an effect results in an overestimation on the secret key rate,and subsequently induces vital practical security loopholes.展开更多
Continuous-variable quantum key distribution(CVQKD) protocols with entanglement in the middle(EM) enable long maximal transmission distances for quantum communications. For the security analysis of the protocols, it i...Continuous-variable quantum key distribution(CVQKD) protocols with entanglement in the middle(EM) enable long maximal transmission distances for quantum communications. For the security analysis of the protocols, it is usually assumed that Eve performs collective Gaussian attacks and there is a lack of finite-size analysis of the protocols. However,in this paper we consider the finite-size regime of the EM-based CVQKD protocols by exposing the protocol to collective attacks and coherent attacks. We differentiate between the collective attacks and the coherent attacks while comparing asymptotic key rate and the key rate in the finite-size scenarios. Moreover, both symmetric and asymmetric configurations are collated in a contrastive analysis. As expected, the derived results in the finite-size scenarios are less useful than those acquired in the asymptotic regime. Nevertheless, we find that CVQKD with entanglement in the middle is capable of providing fully secure secret keys taking the finite-size effects into account with transmission distances of more than 30 km.展开更多
Continuous-variable quantum key distribution (CVQKD) with the local local oscillator (LLO) is confronted with new security problems due to the reference pulses transmitted together with quantum signals over the insecu...Continuous-variable quantum key distribution (CVQKD) with the local local oscillator (LLO) is confronted with new security problems due to the reference pulses transmitted together with quantum signals over the insecure quantum channel. In this paper, we propose a method of phase attack on reference pulses of the LLO-CVQKD with time-multiplexing. Under this phase attack, the phase drifts of reference pulses are manipulated by eavesdroppers, and then the phase compensation error is increased. Consequently, the secret key rate is reduced due to the imperfect phase compensation for quantum signals. Based on the noise model of imperfect phase compensation, the practical security of LLO-CVQKD under phase attack is analyzed. The simulation results show that the practical security is reduced due to the phase attack, yet it is still tight when system parameters are estimated by training signals.展开更多
Compared with the fiber channel,the atmospheric channel offers the possibility of a broader geographical coverage and more flexible transmission for continuous-variable quantum key distribution(CVQKD).However,the fluc...Compared with the fiber channel,the atmospheric channel offers the possibility of a broader geographical coverage and more flexible transmission for continuous-variable quantum key distribution(CVQKD).However,the fluctuation of atmospheric conditions will lead to the loss of performance in atmospheric quantum communication.In this paper,we study how temperature affects atmospheric CVQKD.We mainly consider the temperature effects on the transmittance and interruption probability.From the numerical simulation analysis,it can be shown that the performance of atmospheric CVQKD is improved as temperature increases,with the other factors fixed.Moreover,the results in this work can be used to evaluate the feasibility of the experimental implementation of the atmospheric CVQKD protocols.展开更多
We present a Trojan-horse attack on the practical two-way continuous-variable quantum key distribution system. Our attack mainly focuses on the imperfection of the practical system that the modulator has a redundancy ...We present a Trojan-horse attack on the practical two-way continuous-variable quantum key distribution system. Our attack mainly focuses on the imperfection of the practical system that the modulator has a redundancy of modulation pulsewidth, which leaves a loophole for the eavesdropper inserting a Trojan-horse pulse. Utilizing the unique characteristics of two-way continuous-variable quantum key distribution that Alice only takes modulation operation on the received mode without any measurement, this attack allows the eavesdropper to render all of the final keys shared between the legitimate parties insecure without being detected. After analyzing the feasibility of the attack, the corresponding countermeasures are put forward.展开更多
A modified continuous-variable quantum key distribution （CVQKD） protocol is proposed by originating the entangled source from a malicious third party Eve in the middle instead of generating it from the trustworthy A...A modified continuous-variable quantum key distribution （CVQKD） protocol is proposed by originating the entangled source from a malicious third party Eve in the middle instead of generating it from the trustworthy Alice or Bob. This method is able to enhance the efficiency of the CVQKD scheme attacked by local oscillator （LO） intensity attack in terms of the generated secret key rate in quantum communication. The other indication of the improvement is that the maximum transmission distance and the maximum loss tolerance can be increased significantly, especially for CVQKD schemes based on homodyne detection.展开更多
When developing a practical continuous-variable quantum key distribution(CVQKD),the detector is necessary at the receiver's side.We investigate the practical security of the CVQKD system with an unbalanced heterod...When developing a practical continuous-variable quantum key distribution(CVQKD),the detector is necessary at the receiver's side.We investigate the practical security of the CVQKD system with an unbalanced heterodyne detector.The results show that unbalanced heterodyne detector introduces extra excess noise into the system and decreases the lower bound of the secret key rate without awareness of the legitimate communicators,which leaves loopholes for Eve to attack the system.In addition,we find that the secret key rate decreases more severely with the increase in the degree of imbalance and the excess noise induced by the imbalance is proportional to the intensity of the local oscillator(LO)under the same degree of imbalance.Finally,a countermeasure is proposed to resist these kinds of effects.展开更多
It is shown that the non-Gaussian operations can not only be used to prepare the nonclassical states, but also to improve the entanglement degree between Gaussian states. Thus these operations are naturally considered...It is shown that the non-Gaussian operations can not only be used to prepare the nonclassical states, but also to improve the entanglement degree between Gaussian states. Thus these operations are naturally considered to enhance the performance of continuous variable quantum key distribution(CVQKD), in which the non-Gaussian operations are usually placed on the right-side of the entangled source. Here we propose another scheme for further improving the performance of CVQKD with the entangled-based scheme by operating photon-addition operation on the left-side of the entangled source.It is found that the photon-addition operation on the left-side presents both higher success probability and better secure key rate and transmission distance than the photon subtraction on the right-side, although they share the same maximal tolerable noise. In addition, compared to both photon subtraction and photon addition on the right-side, our scheme shows the best performance and the photon addition on the right-side is the worst.展开更多
We show that the secret key generation rate can be balanced with the maximum secure distance of four-state continuous-variable quantum key distribution（CV-QKD） by using the linear optics cloning machine（LOCM）. Ben...We show that the secret key generation rate can be balanced with the maximum secure distance of four-state continuous-variable quantum key distribution（CV-QKD） by using the linear optics cloning machine（LOCM）. Benefiting from the LOCM operation, the LOCM-tuned noise can be employed by the reference partner of reconciliation to achieve higher secret key generation rates over a long distance. Simulation results show that the LOCM operation can flexibly regulate the secret key generation rate and the maximum secure distance and improve the performance of four-state CV-QKD protocol by dynamically tuning parameters in an appropriate range.展开更多
The advent of quantum computers has significantly challenged the security of traditional cryptographic systems,prompting a surge in research on quantum key distribution(QKD).Among various QKD approaches,continuousvari...The advent of quantum computers has significantly challenged the security of traditional cryptographic systems,prompting a surge in research on quantum key distribution(QKD).Among various QKD approaches,continuousvariable QKD(CVQKD)offers superior resilience against background noise.However,the local local oscillator(LLO)CVQKD scheme faces substantial physical limitations in scenarios with high channel attenuation,and the large attenuation CVQKD remains unrealized.Bottleneck challenges include ensuring stable low-noise transmission and accurately estimating parameters under fluctuating channel conditions.We propose a continuousmode theoretical framework that provides an analytical method for time-varying quantum systems within a freespace channel.This framework can achieve high-fidelity LLO-CVQKD in free space without the need for complex,real-time frequency locking and transmittance calibration equipment.It can also enable free-space QKD under large attenuation and high repetition frequency.Through experimental validation,we first demonstrate high-rate secure quantum key distribution over high-loss free-space channels.Specifically,we achieve asymptotic key rates of 76.366 kbps and 403.896 kbps in 25 dB attenuation free-space channels without turbulence and 21.5 dB average attenuation free-space channels with turbulence,respectively.Additionally,we confirm the feasibility of experiments on mildly turbulent atmospheric channels spanning at least 10.5 km using current equipment.Our scheme provides direct insight into constructing an integrated air-ground quantum communication network.展开更多
Continuous-variable quantum key distribution(CV QKD)using optical coherent detectors is practically favorable due to its low implementation cost,flexibility of wavelength division multiplexing,and compatibility with s...Continuous-variable quantum key distribution(CV QKD)using optical coherent detectors is practically favorable due to its low implementation cost,flexibility of wavelength division multiplexing,and compatibility with standard coherent communication technologies.However,the security analysis and parameter estimation of CV QKD are complicated due to the infinite-dimensional latent Hilbert space.Also,the transmission of strong reference pulses undermines the security and complicates the experiments.In this work,we tackle these two problems by presenting a time-bin-encoding CV protocol with a simple phase-error-based security analysis valid under general coherent attacks.With the key encoded into the relative intensity between two optical modes,the need for global references is removed.Furthermore,phase randomization can be introduced to decouple the security analysis of different photon-number components.We can hence tag the photon number for each round,effectively estimate the associated privacy using a carefully designed coherent-detection method,and independently extract encryption keys from each component.Simulations manifest that the protocol using multi-photon components increases the key rate by two orders of magnitude compared to the one using only the single-photon component.Meanwhile,the protocol with four-intensity decoy analysis is sufficient to yield tight parameter estimation with a short-distance key-rate performance comparable to the best Bennett-Brassard-1984 implementation.展开更多
In the practical continuous-variable quantum key distribution(CV-QKD)system,the postprocessing process,particularly the error correction part,significantly impacts the system performance.Multi-edge type low-density pa...In the practical continuous-variable quantum key distribution(CV-QKD)system,the postprocessing process,particularly the error correction part,significantly impacts the system performance.Multi-edge type low-density parity-check(MET-LDPC)codes are suitable for CV-QKD systems because of their Shannon-limit-approaching performance at a low signal-to-noise ratio(SNR).However,the process of designing a low-rate MET-LDPC code with good performance is extremely complicated.Thus,we introduce Raptor-like LDPC(RL-LDPC)codes into the CV-QKD system,exhibiting both the rate compatible property of the Raptor code and capacity-approaching performance of MET-LDPC codes.Moreover,this technique can significantly reduce the cost of constructing a new matrix.We design the RL-LDPC matrix with a code rate of 0.02 and easily and effectively adjust this rate from 0.016 to 0.034.Simulation results show that we can achieve more than 98%reconciliation efficiency in a range of code rate variation using only one RL-LDPC code that can support high-speed decoding with an SNR less than-16.45 d B.This code allows the system to maintain a high key extraction rate under various SNRs,paving the way for practical applications of CV-QKD systems with different transmission distances.展开更多
Plug-and-play dual-phase-modulated continuous-variable quantum key distribution (CVQKD) protocol can effectively solve the security loopholes associated with transmitting local oscillator (LO). However, this protocol ...Plug-and-play dual-phase-modulated continuous-variable quantum key distribution (CVQKD) protocol can effectively solve the security loopholes associated with transmitting local oscillator (LO). However, this protocol has larger excess noise compared with one-way Gaussian-modulated coherent-states scheme, which limits the maximal transmission distance to a certain degree. In this paper, we show a reliable solution for this problem by employing non-Gaussian operation, especially, photon subtraction operation, which provides a way to improve the performance of plug-and-play dual-phase-modulated CVQKD protocol. The photon subtraction operation shows experimental feasibility in the plug-andplay configuration since it can be implemented under current technology. Security results indicate that the photon subtraction operation can evidently enhance the maximal transmission distance of the plug-and-play dual-phase-modulated CVQKD protocol, which effectively makes up the drawback of the original one. Furthermore, we achieve the tighter bound of the transmission distance by considering the finite-size effect, which is more practical compared with that achieved in the asymptotic limit.展开更多
The effects of weather conditions are ubiquitous in practical wireless quantum communication links.Here in this work,the performances of atmospheric continuous-variable measurement-device-independent quantum key distr...The effects of weather conditions are ubiquitous in practical wireless quantum communication links.Here in this work,the performances of atmospheric continuous-variable measurement-device-independent quantum key distribution(CV-MDI-QKD)under diverse weather conditions are analyzed quantitatively.According to the Mie scattering theory and atmospheric CV-MDI-QKD model,we numerically simulate the relationship between performance of CV-MDI-QKD and the rainy and foggy conditions,aiming to get close to the actual combat environment in the future.The results show that both rain and fog will degrade the performance of the CV-MDI-QKD protocol.Under the rainy condition,the larger the raindrop diameter,the more obvious the extinction effect is and the lower the secret key rate accordingly.In addition,we find that the secret key rate decreases with the increase of spot deflection distance and the fluctuation of deflection.Under the foggy condition,the results illustrate that the transmittance decreases with the increase of droplet radius or deflection distance,which eventually yields the decrease in the secret key rate.Besides,in both weather conditions,the increase of transmission distance also leads the secret key rate to deteriorate.Our work can provide a foundation for evaluating the performance evaluation and successfully implementing the atmospheric CV-MDI-QKD in the future field operation environment under different weather conditions.展开更多
We propose a new scheme to enhance the performance of the Gussian-modulated coherent-state continuous-variable measurement-device-independent quantum key distribution(CV-MDI-QKD)system via quantum scissors(QS)operatio...We propose a new scheme to enhance the performance of the Gussian-modulated coherent-state continuous-variable measurement-device-independent quantum key distribution(CV-MDI-QKD)system via quantum scissors(QS)operation at Bob's side.As an non-deterministic amplifying setup,we firstly introduce the QS-enhanced CV-MDI-QKD protocol and then investigate the success probability of the QS operation in accordance with the equivalent one-way scheme.Afterwards,we investigate the effect of the QS operation on the proposed scheme and analyze the performance of the QS-enhanced CV-MDI-QKD system under the extreme asymmetric circumstance.Simulation results show that the QS operation can indeed improve the performance of the CV-MDI-QKD system considerably.QS-enhanced CV-MDI-QKD protocol outperforms the original CV-MDI-QKD protocol in both the maximum transmission distance and the secret key rate.Moreover,the better the performance of QS operation,the more significant the improvement of performance of the system.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.U1304613 and 11204379)
文摘Information reconciliation is a significant step for a continuous-variable quantum key distribution（CV-QKD） system.We propose a reconciliation method that allows two authorized parties to extract a consistent and secure binary key in a CV-QKD protocol,which is based on Gaussian-modulated coherent states and homodyne detection.This method named spherical reconciliation is based on spherical quantization and non-binary low-density parity-check（LDPC） codes.With the suitable signal-to-noise ratio（SNR） and code rate of non-binary LDPC codes,spherical reconciliation algorithm has a high efficiency and can extend the transmission distance of CV-QKD.
基金Supported by the National Natural Science Foundation of China under Grant No 61572529
文摘Considering the ocean water＇s optical attenuation and the roughness of the sea surface, we analyze the security of continuous-variable （CV） quantum key distribution （QKD） based Mr-to-water channel. The effects of the absorp- tion and scattering on the transmittance of underwater quantum channel and the maximum secure transmission distance are studied. Considering the roughness of the sea surface, we simulate the performance bounds of CV QKD with different wind speeds using the Monte Carlo method. The results show that even if the secret key rate gradually reduces as the wind speed increases, the maximum transmission distance will not be affected obviously. Compared to the works regarding short-distance underwater optical communication, our research represents a significant step towards establishing secure communication between air platform and submarine vehicle.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61332019,61671287,and 61631014)Northwest University Doctorate Dissertation of Excellence Funds,China(Grant No.YYB17022)the National Key Research and Development Program,China(Grant No.2016YFA0302600)
文摘Gaussian-modulated coherent state quantum key distribution is gradually moving towards practical application. Generally, the involved scheme is based on the binary random basis choice. To improve the performance and security, we present a scheme based on a continuous random basis choice. The results show that our scheme obviously improves the performance, such as the secure communication distance. Our scheme avoids comparing the measurement basis and discarding the key bits, and it can be easily implemented with current technology. Moreover, the imperfection of the basis choice can be well removed by the known phase compensation algorithm.
基金supported by the National Natural Science Foundation of China(Grant Nos.62101180 and 61871407)the Key R&D Program of Hunan Province(Grant No.2022GK2016)+1 种基金the State Key Laboratory of High Performance Computing,National University of Defense Technology(Grant No.202101-25)the Fundamental Research Funds for the Central Universities(Grant No.531118010371)。
文摘The trans-media transmission of quantum pulse is one of means of free-space transmission which can be applied in continuous-variable quantum key distribution(CVQKD)system.In traditional implementations for atmospheric channels,the 1500-to-1600-nm pulse is regarded as an ideal quantum pulse carrier.However,the underwater transmission of this pulses tends to suffer from severe attenuation,which inevitably deteriorates the security of the whole CVQKD system.In this paper,we propose an alternative scheme for implementations of CVQKD over satellite-to-submarine channels.We estimate the parameters of the trans-media channels,involving atmosphere,sea surface and seawater and find that the shortwave infrared performs well in the above channels.The 450-nm pulse is used for generations of quantum signal carriers to accomplish quantum communications through atmosphere,sea surface and seawater channels.Numerical simulations show that the proposed scheme can achieve the transmission distance of 600 km.In addition,we demonstrate that non-Gaussian operations can further lengthen its maximal transmission distance,which contributes to the establishment of practical global quantum networks.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61379153 and 61572529)
文摘We propose a method to improve the secret key rate of an eight-state continuous-variable quantum key distribution（CVQKD） by using a linear optics cloning machine（LOCM）. In the proposed scheme, an LOCM is exploited to compensate for the imperfections of Bob＇s apparatus, so that the generated secret key rate of the eight-state protocol could be well enhanced. We investigate the security of our proposed protocol in a finite-size scenario so as to further approach the practical value of a secret key rate. Numeric simulation shows that the LOCM with reasonable tuning gain λ and transmittance τcan effectively improve the secret key rate of eight-state CVQKD in both an asymptotic limit and a finite-size regime.Furthermore, we obtain the tightest bound of the secure distance by taking the finite-size effect into account, which is more practical than that obtained in the asymptotic limit.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61332019,61671287,and 61631014)the National Key Research and Development Program of China(Grant No.2016YFA0302600)
文摘The well-known multi-dimensional reconciliation is an effective method used in the continuous-variable quantum key distribution in the long-distance and the low signal-to-noise-ratio scenarios.The virtual channel employed to exchange data is generally established by using a finite-dimensional rotation in the reconciliation procedure.In this paper,we found that the finite dimension of the multi-dimensional reconciliation inevitably leads to the mismatch of the signal-to-noise-ratio between the quantum channel and the virtual channel,which may be called the finite-dimension effect.Such an effect results in an overestimation on the secret key rate,and subsequently induces vital practical security loopholes.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61572529,61871407,and 61801522)the China Postdoctoral Science Foundation(Grant Nos.2013M542119 and 2014T70772)
文摘Continuous-variable quantum key distribution(CVQKD) protocols with entanglement in the middle(EM) enable long maximal transmission distances for quantum communications. For the security analysis of the protocols, it is usually assumed that Eve performs collective Gaussian attacks and there is a lack of finite-size analysis of the protocols. However,in this paper we consider the finite-size regime of the EM-based CVQKD protocols by exposing the protocol to collective attacks and coherent attacks. We differentiate between the collective attacks and the coherent attacks while comparing asymptotic key rate and the key rate in the finite-size scenarios. Moreover, both symmetric and asymmetric configurations are collated in a contrastive analysis. As expected, the derived results in the finite-size scenarios are less useful than those acquired in the asymptotic regime. Nevertheless, we find that CVQKD with entanglement in the middle is capable of providing fully secure secret keys taking the finite-size effects into account with transmission distances of more than 30 km.
文摘Continuous-variable quantum key distribution (CVQKD) with the local local oscillator (LLO) is confronted with new security problems due to the reference pulses transmitted together with quantum signals over the insecure quantum channel. In this paper, we propose a method of phase attack on reference pulses of the LLO-CVQKD with time-multiplexing. Under this phase attack, the phase drifts of reference pulses are manipulated by eavesdroppers, and then the phase compensation error is increased. Consequently, the secret key rate is reduced due to the imperfect phase compensation for quantum signals. Based on the noise model of imperfect phase compensation, the practical security of LLO-CVQKD under phase attack is analyzed. The simulation results show that the practical security is reduced due to the phase attack, yet it is still tight when system parameters are estimated by training signals.
基金Project supported by the National Natural Science Foundation of China(Grant No.61505261)
文摘Compared with the fiber channel,the atmospheric channel offers the possibility of a broader geographical coverage and more flexible transmission for continuous-variable quantum key distribution(CVQKD).However,the fluctuation of atmospheric conditions will lead to the loss of performance in atmospheric quantum communication.In this paper,we study how temperature affects atmospheric CVQKD.We mainly consider the temperature effects on the transmittance and interruption probability.From the numerical simulation analysis,it can be shown that the performance of atmospheric CVQKD is improved as temperature increases,with the other factors fixed.Moreover,the results in this work can be used to evaluate the feasibility of the experimental implementation of the atmospheric CVQKD protocols.
基金supported by the National Basic Research Program of China(Grant No.2013CB338002)the National Natural Science Foundation of China(Grant Nos.11304397 and 61505261)
文摘We present a Trojan-horse attack on the practical two-way continuous-variable quantum key distribution system. Our attack mainly focuses on the imperfection of the practical system that the modulator has a redundancy of modulation pulsewidth, which leaves a loophole for the eavesdropper inserting a Trojan-horse pulse. Utilizing the unique characteristics of two-way continuous-variable quantum key distribution that Alice only takes modulation operation on the received mode without any measurement, this attack allows the eavesdropper to render all of the final keys shared between the legitimate parties insecure without being detected. After analyzing the feasibility of the attack, the corresponding countermeasures are put forward.
基金supported by the National Natural Science Foundation of China(Grant Nos.61379153,61401519,and 61572529)the Natural Science Foundation of Hunan Province,China(Grant No.2017JJ3415)+1 种基金the Science and Technology Project of Guangxi Zhuang Autonomous Region,China(Grant Nos.AC16380094and 1598008-29)the Natural Science Fund of Guangxi Zhuang Autonomous Region,China(Grant No.2015GXNSFAA139298)
文摘A modified continuous-variable quantum key distribution （CVQKD） protocol is proposed by originating the entangled source from a malicious third party Eve in the middle instead of generating it from the trustworthy Alice or Bob. This method is able to enhance the efficiency of the CVQKD scheme attacked by local oscillator （LO） intensity attack in terms of the generated secret key rate in quantum communication. The other indication of the improvement is that the maximum transmission distance and the maximum loss tolerance can be increased significantly, especially for CVQKD schemes based on homodyne detection.
基金the National Natural Science Foundation of China(Grant No.62001383)the Natural Science Basic Research Plan in Shaanxi Province of China(Grant No.2019JM-591)。
文摘When developing a practical continuous-variable quantum key distribution(CVQKD),the detector is necessary at the receiver's side.We investigate the practical security of the CVQKD system with an unbalanced heterodyne detector.The results show that unbalanced heterodyne detector introduces extra excess noise into the system and decreases the lower bound of the secret key rate without awareness of the legitimate communicators,which leaves loopholes for Eve to attack the system.In addition,we find that the secret key rate decreases more severely with the increase in the degree of imbalance and the excess noise induced by the imbalance is proportional to the intensity of the local oscillator(LO)under the same degree of imbalance.Finally,a countermeasure is proposed to resist these kinds of effects.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11664017 and 11964013)the Training Program for Academic and Technical Leaders of Major Disciplines in Jiangxi Province,China (Grant No. 20204BCJL22053)。
文摘It is shown that the non-Gaussian operations can not only be used to prepare the nonclassical states, but also to improve the entanglement degree between Gaussian states. Thus these operations are naturally considered to enhance the performance of continuous variable quantum key distribution(CVQKD), in which the non-Gaussian operations are usually placed on the right-side of the entangled source. Here we propose another scheme for further improving the performance of CVQKD with the entangled-based scheme by operating photon-addition operation on the left-side of the entangled source.It is found that the photon-addition operation on the left-side presents both higher success probability and better secure key rate and transmission distance than the photon subtraction on the right-side, although they share the same maximal tolerable noise. In addition, compared to both photon subtraction and photon addition on the right-side, our scheme shows the best performance and the photon addition on the right-side is the worst.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61379153 and 61572529)
文摘We show that the secret key generation rate can be balanced with the maximum secure distance of four-state continuous-variable quantum key distribution（CV-QKD） by using the linear optics cloning machine（LOCM）. Benefiting from the LOCM operation, the LOCM-tuned noise can be employed by the reference partner of reconciliation to achieve higher secret key generation rates over a long distance. Simulation results show that the LOCM operation can flexibly regulate the secret key generation rate and the maximum secure distance and improve the performance of four-state CV-QKD protocol by dynamically tuning parameters in an appropriate range.
基金Innovation Program for Quantum Science and Technology(2021ZD0300703)Shanghai Municipal Science and Technology Major Project(2019SHZDZX01)+1 种基金Key R&D Program of Guangdong Province(2020B0303040002)National Natural Science Foundation of China(62101320)。
文摘The advent of quantum computers has significantly challenged the security of traditional cryptographic systems,prompting a surge in research on quantum key distribution(QKD).Among various QKD approaches,continuousvariable QKD(CVQKD)offers superior resilience against background noise.However,the local local oscillator(LLO)CVQKD scheme faces substantial physical limitations in scenarios with high channel attenuation,and the large attenuation CVQKD remains unrealized.Bottleneck challenges include ensuring stable low-noise transmission and accurately estimating parameters under fluctuating channel conditions.We propose a continuousmode theoretical framework that provides an analytical method for time-varying quantum systems within a freespace channel.This framework can achieve high-fidelity LLO-CVQKD in free space without the need for complex,real-time frequency locking and transmittance calibration equipment.It can also enable free-space QKD under large attenuation and high repetition frequency.Through experimental validation,we first demonstrate high-rate secure quantum key distribution over high-loss free-space channels.Specifically,we achieve asymptotic key rates of 76.366 kbps and 403.896 kbps in 25 dB attenuation free-space channels without turbulence and 21.5 dB average attenuation free-space channels with turbulence,respectively.Additionally,we confirm the feasibility of experiments on mildly turbulent atmospheric channels spanning at least 10.5 km using current equipment.Our scheme provides direct insight into constructing an integrated air-ground quantum communication network.
基金Engineering and Physical Sciences Research Council(project EP/T001011/1)Shenzhen-Hong Kong Cooperation Zone for Technology and Innovation(HZQB-KCZYB-2020050)+7 种基金Hong Kong Research Grant Council(R7035-21)Army Research Office(W911NF-23-1-0077)Multidisciplinary University Research Initiative(W911NF-21-1-0325)Air Force Office of Scientific Research(FA9550-19-1-0399,FA9550-21-1-0209)National Science Foundation(OMA-1936118,ERC-1941583,OMA-2137642)NTT ResearchDavid and Lucile Packard Foundation(2020-71479)Marshall and Arlene Bennett Family Research Program。
文摘Continuous-variable quantum key distribution(CV QKD)using optical coherent detectors is practically favorable due to its low implementation cost,flexibility of wavelength division multiplexing,and compatibility with standard coherent communication technologies.However,the security analysis and parameter estimation of CV QKD are complicated due to the infinite-dimensional latent Hilbert space.Also,the transmission of strong reference pulses undermines the security and complicates the experiments.In this work,we tackle these two problems by presenting a time-bin-encoding CV protocol with a simple phase-error-based security analysis valid under general coherent attacks.With the key encoded into the relative intensity between two optical modes,the need for global references is removed.Furthermore,phase randomization can be introduced to decouple the security analysis of different photon-number components.We can hence tag the photon number for each round,effectively estimate the associated privacy using a carefully designed coherent-detection method,and independently extract encryption keys from each component.Simulations manifest that the protocol using multi-photon components increases the key rate by two orders of magnitude compared to the one using only the single-photon component.Meanwhile,the protocol with four-intensity decoy analysis is sufficient to yield tight parameter estimation with a short-distance key-rate performance comparable to the best Bennett-Brassard-1984 implementation.
基金supported by the Key Program of National Natural Science Foundation of China(Grant No.61531003)the National Natural Science Foundation of China(Grant No.62001041)the Fund of State Key Laboratory of Information Photonics and Optical Communications。
文摘In the practical continuous-variable quantum key distribution(CV-QKD)system,the postprocessing process,particularly the error correction part,significantly impacts the system performance.Multi-edge type low-density parity-check(MET-LDPC)codes are suitable for CV-QKD systems because of their Shannon-limit-approaching performance at a low signal-to-noise ratio(SNR).However,the process of designing a low-rate MET-LDPC code with good performance is extremely complicated.Thus,we introduce Raptor-like LDPC(RL-LDPC)codes into the CV-QKD system,exhibiting both the rate compatible property of the Raptor code and capacity-approaching performance of MET-LDPC codes.Moreover,this technique can significantly reduce the cost of constructing a new matrix.We design the RL-LDPC matrix with a code rate of 0.02 and easily and effectively adjust this rate from 0.016 to 0.034.Simulation results show that we can achieve more than 98%reconciliation efficiency in a range of code rate variation using only one RL-LDPC code that can support high-speed decoding with an SNR less than-16.45 d B.This code allows the system to maintain a high key extraction rate under various SNRs,paving the way for practical applications of CV-QKD systems with different transmission distances.
文摘Plug-and-play dual-phase-modulated continuous-variable quantum key distribution (CVQKD) protocol can effectively solve the security loopholes associated with transmitting local oscillator (LO). However, this protocol has larger excess noise compared with one-way Gaussian-modulated coherent-states scheme, which limits the maximal transmission distance to a certain degree. In this paper, we show a reliable solution for this problem by employing non-Gaussian operation, especially, photon subtraction operation, which provides a way to improve the performance of plug-and-play dual-phase-modulated CVQKD protocol. The photon subtraction operation shows experimental feasibility in the plug-andplay configuration since it can be implemented under current technology. Security results indicate that the photon subtraction operation can evidently enhance the maximal transmission distance of the plug-and-play dual-phase-modulated CVQKD protocol, which effectively makes up the drawback of the original one. Furthermore, we achieve the tighter bound of the transmission distance by considering the finite-size effect, which is more practical compared with that achieved in the asymptotic limit.
基金Project supported by the National Natural Science Foundation of China(Grant No.61505261).
文摘The effects of weather conditions are ubiquitous in practical wireless quantum communication links.Here in this work,the performances of atmospheric continuous-variable measurement-device-independent quantum key distribution(CV-MDI-QKD)under diverse weather conditions are analyzed quantitatively.According to the Mie scattering theory and atmospheric CV-MDI-QKD model,we numerically simulate the relationship between performance of CV-MDI-QKD and the rainy and foggy conditions,aiming to get close to the actual combat environment in the future.The results show that both rain and fog will degrade the performance of the CV-MDI-QKD protocol.Under the rainy condition,the larger the raindrop diameter,the more obvious the extinction effect is and the lower the secret key rate accordingly.In addition,we find that the secret key rate decreases with the increase of spot deflection distance and the fluctuation of deflection.Under the foggy condition,the results illustrate that the transmittance decreases with the increase of droplet radius or deflection distance,which eventually yields the decrease in the secret key rate.Besides,in both weather conditions,the increase of transmission distance also leads the secret key rate to deteriorate.Our work can provide a foundation for evaluating the performance evaluation and successfully implementing the atmospheric CV-MDI-QKD in the future field operation environment under different weather conditions.
基金Project supported by the National Natural Science Foundation of China(Grant No.62001383)the Scientific Research Plan Project of Shaanxi Education Department(Natural Science Special Project)(Grant No.19JK0847).
文摘We propose a new scheme to enhance the performance of the Gussian-modulated coherent-state continuous-variable measurement-device-independent quantum key distribution(CV-MDI-QKD)system via quantum scissors(QS)operation at Bob's side.As an non-deterministic amplifying setup,we firstly introduce the QS-enhanced CV-MDI-QKD protocol and then investigate the success probability of the QS operation in accordance with the equivalent one-way scheme.Afterwards,we investigate the effect of the QS operation on the proposed scheme and analyze the performance of the QS-enhanced CV-MDI-QKD system under the extreme asymmetric circumstance.Simulation results show that the QS operation can indeed improve the performance of the CV-MDI-QKD system considerably.QS-enhanced CV-MDI-QKD protocol outperforms the original CV-MDI-QKD protocol in both the maximum transmission distance and the secret key rate.Moreover,the better the performance of QS operation,the more significant the improvement of performance of the system.
