The queueing model for quantum key distribution network

This paper develops a QKD （quantum key distribution）-based queueing model to investigate the data delay on QKD link and network, especially that based on trusted relays. It shows the mean packet delay performance of the QKD system. Furthermore, it proposes a key buffering policy which could effectively improve the delay performance in practice. The results will be helpful for quality of service in practical QKD systems.

Quantum key distribution series network protocol with M-classical Bobs

Secure key distribution among classical parties is impossible both between two parties and in a network. In this paper, we present a quantum key distribution （QKD） protocol to distribute secure key bits among one quantum party and numerous classical parties who have no quantum capacity. We prove that our protocol is completely robust, i.e., any eavesdropping attack should be detected with nonzero probability. Our calculations show that our protocol may be secure against Eve＇s symmetrically individual attack.

Parameter estimation of continuous variable quantum key distribution system via artificial neural networks

Continuous-variable quantum key distribution(CVQKD)allows legitimate parties to extract and exchange secret keys.However,the tradeoff between the secret key rate and the accuracy of parameter estimation still around the present CVQKD system.In this paper,we suggest an approach for parameter estimation of the CVQKD system via artificial neural networks(ANN),which can be merged in post-processing with less additional devices.The ANN-based training scheme,enables key prediction without exposing any raw key.Experimental results show that the error between the predicted values and the true ones is in a reasonable range.The CVQKD system can be improved in terms of the secret key rate and the parameter estimation,which involves less additional devices than the traditional CVQKD system.

Impact of Fiber Dispersion on Performance of Entanglement-Based Dispersive Optics Quantum Key Distribution

Dispersive optics quantum key distribution(DO-QKD)based on energy-time entangled photon pairs is an important QKD scheme.In DO-QKD,the arrival time of photons is used in key generation and security analysis,which would be greatly affected by fiber dispersion.In this work,we establish a theoretical model of the entanglement-based DO-QKD system,considering the protocol,physical processes(such as fiber transmission and single-photon detection),and the analysis of security tests.Based on this theoretical model,we investigate the influence of chromatic dispersion introduced by transmission fibers on the performance of DO-QKD.By analyzing the benefits and costs of dispersion compensation,the system performance under G.652 and G.655 optical fibers are shown,respectively.The results show that dispersion compensation is unnecessary for DO-QKD systems in campus networks and even metro networks.Whereas,it is still required in DO-QKD systems with longer fiber transmission distances.

A full quantum network scheme

We present a full quantum network scheme using a modified BB84 protocol. Unlike other quantum network schemes, it allows quantum keys to be distributed between two arbitrary users with the help of an intermediary detecting user. Moreover, it has good expansibility and prevents all potential attacks using loopholes in a detector, so it is more practical to apply. Because the fiber birefringence effects are automatically compensated, the scheme is distinctly stable in principle and in experiment. The simple components for every user make our scheme easier for many applications. The experimental results demonstrate the stability and feasibility of this scheme.

Multiple stochastic paths scheme on partially-trusted relay quantum key distribution network

Quantum key distribution （QKD） technology provides proven unconditional point-to-point security based on fundamental quantum physics. A QKD network also holds promise for secure multi-user communications over long distances at high-speed transmission rates. Although many schemes have been proposed so far, the trusted relay QKD network is still the most practical and flexible scenario. In reality, the insecurity of certain relay sections cannot be ignored, so to solve the fatal security problems of partially-trusted relay networks we suggest a multiple stochastic paths scheme. Its features are： （i） a safe probability model that may be more practical for real applications; （ii） a multi-path scheme with an upper bound for the overall safe probability; （iii） an adaptive stochastic routing algorithm to generate sufficient different paths and hidden routes. Simulation results for a typical partially-trusted relay QKD network show that this generalized scheme is effective.

Cascading attack on trusted-relay quantum key distribution networks

Trusted relays are the main state-of-the-art way to realize quantum key distribution networks.However,it is hard to require that all nodes in the network are fully trusted.In a multipath keytransmission mechanism,the nodes can be weakly trusted because the secret key can be split into many parts and each part is transmitted to the receiver through a different path.However,if the capacity of a node’s quantum key pool is poorly designed,an attacker,Eve may eavesdrop on the communicating parties’secret message by initiating a redirection attack.In this paper,we show that Eve can trigger a cascading collapse effect by collapsing one of the edges in the network and forcing the communication parties to transmit the message through the nodes controlled by Eve.The influence of the traffic transfer ratio and the control parameters of the edge load on the breakdown probability of the edge are analyzed using a simulation.In order to effectively defend against the cascading attack,it is important for the designer to handle the relationship between the traffic and the capacity of the quantum key pool of each node in the network.

A cost-efficient quantum access network with qubit-based synchronization

Quantum key distribution(QKD)is a physical layer encryption technique that enables two distant parties to exchange secure keys with information-theoretic security.In the last two decades,QKD has transitioned from laboratory research to real-world applications,including multi-user quantum access networks(QANs).This network structure allows users to share a single-photon detector at a network node through time-division multiplexing,thereby significantly reducing the network cost.However,current QAN implementations require additional hardware for auxiliary tasks such as time synchronization.To address this issue,we propose a cost-efficient QAN that uses qubit-based synchronization.In this approach,the transmitted qubits facilitate time synchronization,eliminating the need for additional synchronization hardware.We tested our scheme by implementing a network for two users and successfully achieved average secure key rates of 53.84 kbps and 71.90 kbps for each user over a 50-km commercial fiber spool.In addition,we investigated the capacity of the access network under cross-talk and loss conditions.The simulation results demonstrate that this scheme can support a QAN with 64 users with key rates up to 1070 bps.Our work provides a feasible and cost-effective way to implement a multi-user QKD network,further promoting the widespread application of QKD.

High-quality quantum process tomography of time-bin qubit’s transmission over a metropolitan fiber network and its application

We employ quantum state and process tomography with time-bin qubits to benchmark a city-wide metropolitan quantum communication system.Over this network,we implement real-time feedback control systems for stabilizing the phase of the time-bin qubits and obtain a 99.3%quantum process fidelity to the ideal channel,indicating the high quality of the whole quantum communication system.This allows us to implement a field trial of high-performance quantum key distribution using coherent one way protocol with an average quantum bit error rate and visibility of 0.25%and 99.2%during 12 h over 61 km.Our results pave the way for the high-performance quantum network with metropolitan fibers.

Phase modulation polarization encoding module applied to one-to-many QKD network based on wavelength division multiplexing

The quantum key distribution(QKD)network is a promising solution for secure communications.In this paper,we proposed a polarization-independent phase-modulated polarization encoding module,and it can be combined with a dense wavelength division multiplexer(DWDM)to achieve multi-user QKD.We experimentally test the encoding module with a repetition rate of 62.5 MHz,and its average quantum bit error rate(QBER)is as low as 0.4%.Finally,we implement a principle verification test for simultaneous QKD for 1 to 2 users in 100 min,and the average QBER of two users under the transmission distance of 1 km and 5 km is kept below 0.8%.Due to the use of polarization encoding,the module can also realize scalable network architecture in free-space QKD systems in the future.