We present a method without decoy state to estimate faithfully and efficiently the yield and quantum bit error rate of single photon pulse for BB84 protocol. The numerical calculations show that key generation rate and maximal secure communication distance of our method are better than results of the decoy state method. As we know, it is the first time we present this method and the idea is very novel. Furthermore, our method can overcome the drawbacks of decoy state method. In our method, the maximal secure distance is insensitive to the deviation of dark count rate from exact value.
We present a method without decoy state to estimate faithfully and efficiently the yield and quantum bit error rate of single photon pulse for BB84 protocol. The numerical calculations show that key generation rate and maximal secure communication distance of our method are better than results of the decoy state method. As we know, it is the first time we present this method and the idea is very novel. Furthermore, our method can overcome the drawbacks of decoy state method. In our method, the maximal secure distance is insensitive to the deviation of dark count rate from exact value.
In this paper, we provide a simple approach for determining the rate of secure key production when single-photon and two-photon pulses are used to generate the secure key. For both BB84 and SARG04, we offer estimation and optimization of decoy-state parameters for a single decoy state protocol and two decoy state protocols. This method can be used to determine the lower bound on the fraction of single-photon counts ([Formula: see text]), the fraction of two-photon counts ([Formula: see text]), the upper bound on the QBER of single-photon pulses ([Formula: see text]), the upper bound on the QBER of two-photon pulses ([Formula: see text]), and the lower bound on the key generation rate for both BB84 and SARG04. Due to the limited data size in real-world experiments, we estimate the statistical fluctuations of several parameters, including the gain and QBER of the signal state, as well as the gain and QBER of the decoy state, which are used to estimate the lower bound of key generation rate. We propose formulae that specify the optimal decoy and signal state percentages and intensities. Then we can determine the maximum and optimal key generation rate. For both SARG04 and BB84, we simulated a free space-based QKD system using our decoy state strategy. The simulation results show that free space-based QKD systems that use the suggested approach for BB84 can achieve a higher secret key rate and a greater safe distance than SARG04-based systems.
Based on the heralded pair-coherent states sources, the Vacuum+Weak decoy state protocol focused on BB84 is presented. Combining the passive decoy state method and the active decoy state method, we use the triggered and nontriggered components to estimate the fraction of single-photon counts and quantum bit-error rate of single-photon and to generate the secure key. From the simulation results of the final key rate over the distance, which shows that our method improve the QKD performance and obtain higher key generation rate than that of the active decoy states method.
We generalize BB84 quantum key distribution (QKD) to the scenario where the receiver adopts a heralded quantum memory (QM). With the heralded QM, the valid dark count rate of the receiver’s single photon detectors can be mitigated obviously, which will lower the quantum bit error rate, and thus improve the performance of decoy-state BB84 QKD systems in long distance range. Simulation results show that, with practical experimental system parameters, decoy-state BB84 QKD with QM can exhibit performance comparable to that of without QM in short distance range, and exhibit performance better than that without QM in long distance range.
Quantum key distribution (QKD) allows two parties to communicate in absolute security based on the fundamental laws of physics. Up till now, it is widely believed that unconditionally secure QKD based on standard Bennett-Brassard (BB84) protocol is limited in both key generation rate and distance because of imperfect devices. Here, we solve these two problems directly by presenting new protocols that are feasible with only current technology. Surprisingly, our new protocols can make fiber-based QKD unconditionally secure at distances over 100km (for some experiments, such as GYS) and increase the key generation rate from O(η2) in prior art to O(η) where η is the overall transmittance. Our method is to develop the decoy state idea (first proposed by W.-Y. Hwang in "Quantum Key Distribution with High Loss: Toward Global Secure Communication", Phys. Rev. Lett. 91, 057901 (2003)) and consider simple extensions of the BB84 protocol. This part of work is published in "Decoy State Quantum Key Distribution", . We present a general theory of the decoy state protocol and propose a decoy method based on only one signal state and two decoy states. We perform optimization on the choice of intensities of the signal state and the two decoy states. Our result shows that a decoy state protocol with only two types of decoy states—a vacuum and a weak decoy state—asymptotically approaches the theoretical limit of the most general type of decoy state protocols (with an infinite number of decoy states). We also present a one-decoy-state protocol as a special case of Vacuum+Weak decoy method. Moreover, we provide estimations on the effects of statistical fluctuations and suggest that, even for long distance (larger than 100km) QKD, our two-decoy-state protocol can be implemented with only a few hours of experimental data. In conclusion, decoy state quantum key distribution is highly practical. This part of work is published in "Practical Decoy State for Quantum Key Distribution", . We also have done the first experimental demonstration of decoy state quantum key distribution, over 15km of Telecom fibers. This part of work is published in "Experimental Decoy State Quantum Key Distribution Over 15km", .
Abstract: The quantum key distribution (QKD) technique establishes secret keys shared between two communicating parties. Theoretically, unconditional security provided by QKD is guaranteed by the fundamental laws of quantum physics. in the real life, it is still possible to obtain unconditionally secure QKD, even with (phase randomized) attenuated laser pulses, as theoretically demonstrated by Gottesman-Lo-L¨utkenhaus-Preskill (GLLP). However, one must pay a steep price by placing severe limits on the distance and the key generation rate. These problems were solved using the decoy state method introduced by Hwang. In this paper, we have proposed a method to estimate parameters of the decoy state method based on two decoy state protocol for both BB84 and SARG04. The vacuum and weak decoy state protocol has been introduced as a special case of two decoy states protocol. This method has given different lower bound of the fraction of single-photon counts (y1), the fraction of two-photon counts (y2), the upper bound QBER of single-photon pulses (e1), the upper bound QBER of two-photon pulses (e2) and the lower bound of key generation rate for both BB84 and SARG04. The fiber based QKD systems also have been simulated using the proposed method for BB84 and SARG04. The numerical simulation has shown that the fiber based QKD systems using the proposed method for BB84 are able to achieve both a higher secret key rate and greater secure distance than that of SARG04. Key words: Quantum cryptography Quantum key distribution Decoy state protocol and optical communications
This paper simulated the operation of vacuum state and single decoy state protocols in the BB84 and SARG04 QKD schemes by utilizing the features of the commercial ID-3000 QKD system. Numerical modeling identified an optimal signal-to-decoy state ratio of 0.95:0.05 and an intensity of μ=0.85 for the signal state and ν1=0.05 for the decoy state, ensuring the highest key generation rate and a secure distance of up to 50 km. These protocols were validated experimentally over various transmission distances with standard telecom fiber, using the ID-3000 QKD system in a conventional bi-directional plug-and-play setup. Simulations predicted secure key rates of 1.2 × 10 5 bits/s for SARG04 and 8.5 × 104 bits/s for BB84 at 10 km, with secure distances of 45 km and 35 km, respectively. The experimental results confirmed these predictions, showing a 30% higher key rate and 20% longer secure distance compared to non-decoy methods. The SARG04 protocol surpassed BB84 in key rate and secure distance, highlighting the two-photon component's role in key generation. This study concludes that the decoy-state method significantly enhances key generation rates and secure distances, optimizing QKD protocols for secure quantum communication.