As one of the most common weathers in daily life, the rain can change the atmospheric compositions and humidity in a short time, which may cause non-ignorable attenuation in free-space quantum communication system. Besides, the absorption and scattering effects caused by raindrops can also bring huge attenuation to photon's propagation. In order to solve this burst interference caused by rain weather, optimal mean photon number per pulse and chameleon self-adaptive algorithm (CSA) are proposed based on the rainfall distribution model and decoy-state quantum key distribution. Due to the lack of producing mature ideal single photon source technology, the decoy-state protocol with highly attenuated laser becomes the most practical and most widely used quantum secure communication protocol currently. Among all the different kinds of decoy-state protocols, the vacuum+weak decoy state quantum communication secure protocol is chosen to be the basis of our research. Besides, in order to study the influence of mean photon number per signal pulse, we set the pulse ratio between signal state, decoy state and vacuum state to be fixed at 2:2:1. Since the performance of the vacuum+weak decoy state quantum communication system is closely related to the mean photon number per pulse, it is very necessary to confirm the optimal value. Combining the Weibull rainfall distribution model and Mie scattering theory, we first analyze the attenuation caused by rainfall in a free-space quantum communication system. Then the functional relationship among opt, rainfall intensity (J) and link distance (L) is built by studying the propagation of highly attenuated laser in depolarizing channel. Finally, two parameters, secure key rate and channel survival function, are chosen to evaluate the system's performance of reliability and validity. These two parameters are respectively compared between the system with and without CSA. Simulation results show that, as J=30 mm/24 h, L=30 km, the secure key generation rate rises from 210-4 up to 3.510-4 when using the CSA in the quantum communication system; as J=60 mm/24 h, L=20 km, the quantum channel survival function value increases from 0.52 to 0.63; as the quantum channel survival function value is required no lower than 0.5, the rainfall intensity in which quantum communication system can survive rises from 62 mm/24 h up to 74 mm/24 h. These results prove that there is a close relationship between opt and the channel parameters of the quantum communication system under the background of rainfall. Therefore, it is necessary for us to self-adapt the opt value by combining rainfall intensity with the CSA strategy if the reliability and survivability of free space quantum communication system are required to be improved.
As one of the most common weathers in daily life, the rain can change the atmospheric compositions and humidity in a short time, which may cause non-ignorable attenuation in free-space quantum communication system. Besides, the absorption and scattering effects caused by raindrops can also bring huge attenuation to photon's propagation. In order to solve this burst interference caused by rain weather, optimal mean photon number per pulse and chameleon self-adaptive algorithm (CSA) are proposed based on the rainfall distribution model and decoy-state quantum key distribution. Due to the lack of producing mature ideal single photon source technology, the decoy-state protocol with highly attenuated laser becomes the most practical and most widely used quantum secure communication protocol currently. Among all the different kinds of decoy-state protocols, the vacuum+weak decoy state quantum communication secure protocol is chosen to be the basis of our research. Besides, in order to study the influence of mean photon number per signal pulse, we set the pulse ratio between signal state, decoy state and vacuum state to be fixed at 2:2:1. Since the performance of the vacuum+weak decoy state quantum communication system is closely related to the mean photon number per pulse, it is very necessary to confirm the optimal value. Combining the Weibull rainfall distribution model and Mie scattering theory, we first analyze the attenuation caused by rainfall in a free-space quantum communication system. Then the functional relationship among opt, rainfall intensity (J) and link distance (L) is built by studying the propagation of highly attenuated laser in depolarizing channel. Finally, two parameters, secure key rate and channel survival function, are chosen to evaluate the system's performance of reliability and validity. These two parameters are respectively compared between the system with and without CSA. Simulation results show that, as J=30 mm/24 h, L=30 km, the secure key generation rate rises from 210-4 up to 3.510-4 when using the CSA in the quantum communication system; as J=60 mm/24 h, L=20 km, the quantum channel survival function value increases from 0.52 to 0.63; as the quantum channel survival function value is required no lower than 0.5, the rainfall intensity in which quantum communication system can survive rises from 62 mm/24 h up to 74 mm/24 h. These results prove that there is a close relationship between opt and the channel parameters of the quantum communication system under the background of rainfall. Therefore, it is necessary for us to self-adapt the opt value by combining rainfall intensity with the CSA strategy if the reliability and survivability of free space quantum communication system are required to be improved.
Quantum information technology is an emerging interdisciplinary field that utilizes the properties of quantum mechanics and combines classical information theory and methods to represent and process information. Among them, quantum secure communication (especially quantum key distribution technology) is considered one of the most likely directions to be put into practical use first. According to different propagation media, quantum key distribution can be divided into quantum key distribution in optical fibers and quantum key distribution in free space. There is nobirefringence effect in optical fibers of the free space, and there is no need to lay optical cables. Once the technology is mature, it can be used for secure ground satellite communication, building a global network of quantum communication networks, and has good development prospects. Due to the complex weather conditions above the channel, the attenuation of laser power in the atmosphere is difficult to predict. This article focuses on theoretical modeling of commonly used aerosols in channels. By analysing the advantages and disadvantages of existing models, a micro particle scattering method is proposed to construct atmospheric attenuation, which introduces geometric scattering and cladding particle scattering. Extended Mie scattering models are constructed separately, and the applicable objects and scope of the scattering models are explained. Mie scattering is a theoretical model for analyzing the attenuation of fog aerosols, while geometric scattering is a theoretical method for analyzing large-scale aerosols such as rainfall. For haze aerosols, a blanket particle scattering model is proposed for theoretical analysis. When the aerosol concentration is high, Monte Carlo method can be combined for optimization. Then, based on the layered theory, the attenuation of laser propagation along any path is derived. Finally, attenuation models for fog, rain, and haze were constructed. On this basis, the attenuation of laser propagation along any path is derived. Then, the simulation results are compared with mainstream commercial software, and the relative error of operation is less than 5%. Finally, the results were compared uniformly to determine the strength of aerosol attenuation on the 1.55u m laser. The simulation results of the model can serve as a theoretical basis for the adaptive power adjustment of the free space quantumkey distribution system at the transmitting, ensuring the system's error rate.
Problem statement: Quantum key distribution provides unconditional security guaranteed by the fundamental laws of quantum physics. Unfortunately, for real-life experimental set-ups, which mainly based on faint laser pulses, the occasional production of multi-photons and channel loss make it possible for sophisticated eavesdroppers to launch various subtle eavesdropping attacks including the Photon Number Splitting (PNS) attack. The decoy state protocols recently proposed to beat PNS attack and to improve dramatically distance and secure key generation rate of Quantum Key Distribution (QKD). Approach: Objective of this study was experimental implementation of weak decoy + vacuum states QKD for increasing the performance of QKD system. To show conceptually how simple it was to apply the weak decoy + vacuum state idea to a commercial QKD system, we chosen ID-3000 commercial quantum key distribution system manufactured by id quantique. To implement the weak decoy + vacuum state protocol, we had to add some new optical and electronics components to id quantique and to attenuate each signal to the intensity of either signal state or weak decoy or vacuum state randomly. Results: In our implementation, the attenuation will be done by placing a VOA (variable optical attenuator) in Alice’s side. Specifically, our QKD system required the polarizations of 2 pulses from the same signal to be orthogonal. Therefore the VOA must be polarization independent so as to attenuate the two pulses equally. The VOA utilized in experiment to attenuate signals dynamically was Intensity Modulator (IM). We had implemented weak + vacuum protocol on a modified commercial QKD system over a 25 km of telecom fibers with an unconditionally secure key rate of 6.2931×10-4 per pulse. Conclusion: By making simple modifications to a commercial quantum key distribution system, we could achieve much better performance with substantially higher key generation rate and longer distance than QKD system without decoy state.
Quantum satellite communication is an essential part in building a global quantum communication network. In order to cope with the sudden interference brought by snowfall to the quantum satellite communication system, an adaptive adjustment strategy for quantum satellite communication performance based on the optimal average photon number is proposed based on the decoy state protocol and snowfall spectral distribution function for the depolarization channel characteristics. The relationship between snowfall intensity and communication elevation angle and the optimal average number of photons per pulse is established, and the bit error ratio(BER) and survival performance of the system before and after the adoption of this strategy is compared. The simulation results show that the BER of the system decreases from 0.07 and 0.085 to 0.046 and 0.064 for medium and heavy snowfall environments, respectively; if the minimum communication elevation angle is required to be 0.81, the survival capability of the system increases from 0.81 to 0.92 for heavy snowfall environment; if the channel survival capability is required to be 0.8, the minimum communication elevation angle of the satellite link can be adjusted from 26° to 18° for heavy snowfall environment. Therefore, the strategy proposed enables the system to cope with more intense snowfall, improves the transmission quality of small elevation angle communication, further reduces the BER of the quantum satellite communication system, and enhances the reliability of the system in the snowfall context.
In order to study the effect of the coexistence of rain and fog on the communication performance of satellite terrestrial quantum link, the relationship between link attenuation and transmission distance and visibility was analyzed based on the attenuation model of optical quantum under the coexistence of rain and fog, and the influence of the coexistence of rain and fog on channel capacity, channel fidelity, channel survival function and channel bit error rate was studied. The findings reveal that at a visibility of 0.5 km and a transmission distance of 0.3 km, the link experiences an attenuation of1 0. 2 2 d B⋅k m−1. Furthermore, at the same visibility of 0.5 km and transmission distance of 0.25 km, the channel capacities for the amplitude damped and depolarized channels are recorded as 0.41 bit/sand 0.29 bit/s respectively. When visibility is 0.5 km and transmission distance is 0.3 km, the survival function values of amplitude damped channel and depolarized channel are 0.901 and 0.979 respectively. At a visibility of 0.5 km and with a transmission distance of 1 km, the channel's bit error rate reaches 0.24. Consequently, the coexistence of rain and fog significantly affects the efficiency of satellite terrestrial quantum communication systems. System parameters should be adjusted adaptively according to different environmental parameters to ensure the stability and reliability of the system.
Abstract Ideal quantum key distribution (QKD) protocols require perfect single photon sources, detectors, and lossless channels. However, the present technology cannot ensure all of the requirements. Among the variants of practical QKD schemes, decoy state QKD in its present form approaches nearly the theoretical security. In any decoy state method, a compromise is made between the security of the key distribution and the rate of key generation by optimizing the two major protocol parameters: the number of decoy states and their relative intensities, and the length of the data string as well. Use of more number of decoy states and higher range of intensities though improve security, their optimization becomes too complex. Therefore, from practical consideration, some restrictions are to be imposed on the choice of decoy states and their intensities. In addition, the treatment of correlations among the laser pulses in security analysis is not fully understood. Normally, lack of correlations or randomness among the signal states is considered to gain security, but, in a different approach, described in the proposed protocol, additional correlation is introduced to improve key generation rate without compromising security. To do that, a one-way function is shared among the legitimate users to provide a semi-random choice of bases depending on the outcome of the receiver’s detector. The initial communication is made through a set of bits with predefined bases and intensity distribution. Then, with the help of the positive outcome of the receiver’s detector, the basis set as well as the length of the bit string for subsequent communications are computed. This results in correlation among the bases and the relative intensities of the signal states and provides a self-checking mechanism to identify eavesdropping. The security analysis of the protocol provides a low error rate and a relatively high key generation rate.
Abstract This paper proposes a new quantum key distribution(QKD) protocol, namely the pseudo-random bases entangled photon based QKD (PRB-EPQKD) protocol. The latest mainly focuses on three properties, including the security of the protocol, the secure key size and the maximum communication distance between legitimate communication users (Alice and Bob). To achieve this, we first consider a spontaneous-parametric-down (SPDC) photon source located in a low-earth-orbit (LEO) type satellite capable of producing and distributing entangled photons pairs to Alice and Bob. Secondly, we assume that Alice's and Bob's photons state measurement bases are identically generated via a pseudo-random number generator (PRNG), namely the quantum logistic map (QLM). Finally, we also assume that in addition to their photons states, Alice and Bob intentionally share a set of decoy states at each pulse with randomly selected intensity, and with the goal to detect the presence of the eavesdropper (Eve). Under these considerations, the secure key rate upper bound is evaluated applying the Gottesman-Lo-Lutkenhaus-Preskill's (GLLP) formula, for two different implementations, namely the non-decoy states and the infinite active decoy states based QKD. It is observed a significant improvement in the secure key size and the communication distance as well, compared to existing protocols, since we realize that under daylight, downlinks satellite conditions, a kindly selected light source, and good crystal's properties, the maximum communication distance can reach up to 70000 km. In addition, using the combined type-I and type-II SPDC photons source as our entangled photons pairs generator, significantly improved the photon mean number and render our protocol more robust against photon number division attack and against attenuation-induced atmospheric propagation. Furthermore, the protocol is more secure as compared to existing ones, given that any eavesdropper must crack simultaneously the chaotic system used as PRNG and the QKD system, before getting any useful information as regards to the measurement bases used by Alice and Bob, and thus the secure key.