Secure Communication Distance Research Articles

Enhancing Quantum Key Distribution Protocols for Extended Range and Reduced Error

Abstract this paper proposes an optimized Quantum Key Distribution (QKD) protocol using entanglement swapping techniques to extend transmission range and improve error correction. Additionally, integrates an advanced error correction technique which is Low Density Parity Check (LDPC) and multi-hop quantum repeaters for more enhancement of the protocol performance. Hybrid Quantum Classical Error Correction Methods is applied ensuring compatibility and optimal performance and to manage the increased complexity. Simulations prove that 25% improvement in transmission distance with entanglement swapping. 50% improvement with advanced error correction and a 100% improvement with multi-hop quantum repeaters compared to existing protocols. These discoveries are supported by both theoretical analysis and simulation results, indicating significant decreases in error rates and extensions in maximum transmission distances. Comparative analysis made with existing protocols and that demonstrated the superiority of proposed approach in terms of extended secure communication distance, higher key generation rate and improved resilience to attacks.

Device-Independent Quantum Secure Direct Communication with Single-Photon Sources

Quantum secure direct communication (QSDC) can directly transmit secrete messages through a quantum channel. Device-independent (DI) QSDC can guarantee the communication security relying only on the observation of the Bell-inequality violation, but not on any detailed description or trust of the inner workings of users' devices. In the paper, we propose a DI-QSDC protocol with practical highly efficient single-photon sources. The communication parties construct the entanglement channel from single photons by adopting the heralded architecture, which makes the message-leakage rate independent of the photon-transmission loss. The secure communication distance and the practical communication efficiency of the current DI-QSDC protocol are about 6 times and 600 times of those in the original DI-QSDC protocol. Combining with the entanglement purification, the parties can construct the nearly perfect entanglement channel and completely eliminate the message leakage. This DI-QSDC protocol may have useful applications in the future quantum communication field.

Photon subtraction-based continuous-variable measurement-device-independent quantum key distribution with discrete modulation over a fiber-to-water channel

We propose a discrete-modulated continuous-variable measurement-device-independent quantum key distribution protocol over a fiber-to-water channel. Different from optical fibers, the underwater channel has more severe optical attenuation because of optical absorption and scattering, which reduces the maximum communication distance. To enhance the performance of the protocol, the photon subtraction operation is implemented at the modulator side. We carry out a performance simulation in two different kinds of seawater channel, and the result shows that the scheme with photon subtraction has a longer secure communication distance under certain conditions.

Triggering parametric-down conversion-based quantum key distribution via radiation field

We discuss the influence of radiation field on the secure key size and the maximum safety distance during QKD by using a set of photons produced via a spontaneous parametric-down conversion (SPDC) photon source. Four implementations that use multiple-photons and decoy states are discussed, these include nondecoy state, infinite active decoy state, passive decoy state with threshold detector and passive decoy state with perfect photon-number resolving detector. Results show that the radiation field significantly improves both the secure key size and the maximum secure communication distance. Therefore, the radiation field is found to be a good candidate to reduce unwanted interactions of photons with the quantum channel and hence, to increase the secure key rate and the maximum safety distance between legitimate users.

The Decoy-State Measurement-Device-Independent Quantum Key Distribution with Heralded Single-Photon Source

Based on heralded single-photon source (HSPS), a decoy-state measurement-device-independent quantum key distribution (MDI-QKD) protocol is proposed in this paper. The MDI-QKD protocol mainly uses orbital angular momentum (OAM) states and pulse position modulation (PPM) technology to realize the coding of the signal states in heralded single-photon source. The three-intensity decoy states are used to avoid the attacks against the light source. Moreover, the formula of key generation rate is given by computing the lower bound of the yield of single-photon pairs and the upper bound of the error rate of single-photon pairs. Numerical simulation shows that the new MDI-QKD protocol has high key generation rate and low error rate. Moreover, the secure communication distance can be up to 450 km.

Performance of underwater quantum key distribution with polarization encoding.

Underwater quantum key distribution (QKD) has potential applications in absolutely secure underwater communication. However, the performance of underwater QKD is limited by the optical elements, background light, and dark counts of the detector. In this paper, we propose a modified formula for the quantum bit error rate (QBER), which takes into account the effect of detector efficiency on the QBER caused by the background light. Then we calculate the QBER of the polarization encoding BB84 protocol in Jerlov-type seawater by analyzing the effect of the background light and optical components in a more realistic situation. Finally, we further analyze the final key rate and the maximum secure communication distance in three propagation modes, i.e., upward, downward, and horizontal modes. We find that secure QKD can be performed in the clearest Jerlov-type seawater at a distance of hundreds of meters, even in the worst downward propagation mode. Specifically, by optimizing the system parameters, it is possible to securely transmit information with a rate of 67kbits/s at a distance of 100m in the seawater channel with an attenuation coefficient of 0.03/m at night. For practical underwater QKD, the performance can also be improved by using decoy states. Our results are useful for long-distance underwater quantum communication.

Quantum communication improved by spectral entanglement and supplementary chromatic dispersion

Implementations of many quantum communication protocols require sources of photon pairs. However, optimization of the properties of these photons for specific applications is an open problem. We theoretically demonstrate the possibility of extending the maximal distance of secure quantum communication when a photon pair source and standard fibers are used in a scenario where Alice and Bob do not share a global time reference. It is done by manipulating the spectral correlation within a photon pair and by optimizing chromatic dispersion in transmission links. Contrary to typical expectations, we show that in some situations the secure communication distance can be increased by introducing some extra dispersion.

Continuous-variable quantum key distribution based on continuous random basis choice**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), and the National Key Research and Development Program, China (Grant No. 2016YFA0302600).

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.

Practical decoy state quantum key distribution with detector efficiency mismatch

Decoy state method is widely used in practical quantum key distribution (QKD) systems to substantially extend the secure communication distance. Detector efficiency mismatch (DEM), which exists between practical detectors, effects the security of practical QKD systems seriously. Security of single photon QKD with DEM has been analyzed. However, estimate of the phase error rate still remains difficult in practice. Here, using a simple equivalent detection model, the mutual information between legitimate users and the eavesdropper for single photon state in QKD with DEM is analyzed. Then we improve the security analysis to cover the situation of weak coherent QKD with DEM. A general theory of the decoy state QKD with DEM is proposed to calculate the lower bound of count rate and the upper bound of error rate of single photon state signals. The numerical simulations show that secure key can also be generated, but the existing of DEM will reduce the secure key of practical decoy state QKD systems. The experiment parameter related security bound of DEM is also given out.

Reference-Frame-Independent and Measurement-Device-Independent Quantum Key Distribution Using One Single Source

Measurement-device-independent quantum key distribution (MDI-QKD) is immune to all detector side-channel attacks. However, practical implementations of MDI-QKD, which require two-photon interferences from separated independent single-photon sources and a nontrivial reference alignment procedure, are still challenging with current technologies. Here, we propose a scheme that significantly reduces the experimental complexity of two-photon interferences and eliminates reference frame alignment by the combination of plug-and-play and reference frame independent MDI-QKD. Simulation results show that the secure communication distance can be up to 219 km in the finite-data case and the scheme has good potential for practical MDI-QKD systems.

A long-distance quantum key distribution scheme based on pre-detection of optical pulse with auxiliary state**Project supported by the National Natural Science Foundation of China (Grant No. 61372076), the Programme of Introducing Talents of Discipline to Universities, China (Grant No. B08038), and the Fundamental Research Funds for the Central Universities, China (Grant No. K5051201021).

We construct a circuit based on PBS and CNOT gates, which can be used to determine whether the input pulse is empty or not according to the detection result of the auxiliary state, while the input state will not be changed. The circuit can be treated as a pre-detection device. Equipping the pre-detection device in the front of the receiver of the quantum key distribution (QKD) can reduce the influence of the dark count of the detector, hence increasing the secure communication distance significantly. Simulation results show that the secure communication distance can reach 516 km and 479 km for QKD with perfect single photon source and decoy-state QKD with weak coherent photon source, respectively.

High performance reconciliation for continuous-variable quantum key distribution with LDPC code

Reconciliation is a significant procedure in a continuous-variable quantum key distribution (CV-QKD) system. It is employed to extract secure secret key from the resulted string through quantum channel between two users. However, the efficiency and the speed of previous reconciliation algorithms are low. These problems limit the secure communication distance and the secure key rate of CV-QKD systems. In this paper, we proposed a high-speed reconciliation algorithm through employing a well-structured decoding scheme based on low density parity-check (LDPC) code. The complexity of the proposed algorithm is reduced obviously. By using a graphics processing unit (GPU) device, our method may reach a reconciliation speed of 25 Mb/s for a CV-QKD system, which is currently the highest level and paves the way to high-speed CV-QKD.

Analysis of statistical fluctuation in decoy state quantum key distribution system

Decoy state has proven to be a very useful method of significantly enhancing the performance of a quantum key distribution (QKD) system with practical light sources. The data-set size in practical QKD protocol is always finite, which will cause statistical fluctuations. The gain and the error rate of the quantum state are analyzed by considering absolutely statistical fluctuation. The relation between key generation rate and the secure communication distance is shown with exchanged quantum signal (N = 106 -1012) by the method of two-decoy-state protocol under the condition that communication wavelength is 1310 nm (or1550 nm). The result indicates that the minimal number of exchanged quantum signals increases obviously with the increase of transmission distance. The secure transmission distance is 135 km under the condition that quantum signal is 1012.

Analysis of the differential-phase-shift-keying protocol in the quantum-key-distribution system

The analysis is based on the error rate and the secure communication rate as functions of distance for three quantum-key-distribution (QKD) protocols: the Bennett–Brassard 1984, the Bennett–Brassard–Mermin 1992, and the coherent differential-phase-shift keying (DPSK) protocols. We consider the secure communication rate of the DPSK protocol against an arbitrary individual attack, including the most commonly considered intercept-resend and photon-number splitting attacks, and concluded that the simple and efficient differential-phase-shift-keying protocol allows for more than 200 km of secure communication distance with high communication rates.

Decoy State Quantum Key Distribution with Odd Coherent State

We propose a decoy state quantum key distribution scheme with odd coherent state which follows sub-Poissonian distributed photon count and has low probability of the multi-photon event and vacuum event in each pulse. The numerical calculations show that our scheme can improve efficiently the key generation rate and secure communication distance. Furthermore, only one decoy state is necessary to approach to the perfect asymptotic limit with infinite decoy states in our scheme, but at least two decoy states are needed in other scheme.

Analysis of differential-phase-shift keying protocol for a two-way quantum-key-distribution system

The performance of a two-way quantum-key-distribution (QKD) system are analyzed using the differential-phase-shift keying (DPSK) protocol. The comparison is based on the secure communication rate as a function of distance for three QKD protocols: the Bennett-Brassard 1984, the Bennett-Brassard-Mermin 1992, and the coherent differential-phase-shift keying protocols. We discussed the security of DPSK protocol against any type of individual photon splitting attack and concluded that the simple and efficient DPSK protocol allows for more than 200km of secure communication distance with high communication rates.