Measurement-device-independent Quantum Key Distribution Research Articles

Practical Performance Analysis of MDI-QKD with Orbital Angular Momentum on UAV Relay Platform.

The integration of terrestrial- and satellite-based quantum key distribution (QKD) experiments has markedly advanced global-scale quantum networks, showcasing the growing maturity of quantum technologies. Notably, the use of unmanned aerial vehicles (UAVs) as relay nodes has emerged as a promising method to overcome the inherent limitations of fiber-based and low-Earth orbit (LEO) satellite connections. This paper introduces a protocol for measurement-device-independent QKD (MDI-QKD) using photon orbital angular momentum (OAM) encoding, with UAVs as relay platforms. Leveraging UAV mobility, the protocol establishes a secure and efficient link, mitigating threats from untrusted UAVs. Photon OAM encoding addresses reference frame alignment issues exacerbated by UAV jitter. A comprehensive analysis of atmospheric turbulence, state-dependent diffraction (SDD), weather visibility, and pointing errors on free-space OAM-state transmission systems was conducted. This analysis elucidates the relationship between the key generation rate and propagation distance for the proposed protocol. Results indicate that considering SDD significantly decreases the key rate, halving previous data results. Furthermore, the study identifies a maximum channel loss capacity of 26 dB for the UAV relay platform. This result is pivotal in setting realistic parameters for the deployment of UAV-based quantum communications and lays the foundation for practical implementation strategies in the field.

Boosting asymmetric measurement-device-independent quantum key distribution via numerical-analysis technology

Asymmetric measurement-device-independent quantum key distribution (MDI-QKD) enables building a scalable, high-rate quantum network with an untrusted relay in real-world scenarios. In this study, we improve the performance of asymmetric MDI-QKD using numerical analysis techniques. Simulation results show a twofold increase in tolerance to basis misalignment compared to the previous state-of-the-art method. Specifically, for instances of substantial basis misalignment, the key rate increases by an order of magnitude, and the maximum communication distance extends by 20 km. Our work significantly enhances the robustness and feasibility of asymmetric MDI-QKD, thereby promoting the widespread deployment of MDI-QKD networks.

Measurement device-independent quantum key distribution with vector vortex modes under diverse weather conditions

Most quantum key distribution schemes exploiting orbital angular momentum-carrying optical beams are based on conventional set-ups, opening up the possibility of detector side-channel attacks. These optical beams also suffer from spatial aberrations due to atmospheric turbulence and unfavorable weather conditions. Consequently, we introduce a measurement device-independent quantum key distribution implemented with vector vortex modes. We study the transmission of vector vortex and scalar beams through a turbulent atmospheric link under diverse weather conditions such as rain or haze. We demonstrate that a maximum secure key transmission distance of 178 km can be achieved under clear conditions by utilizing the vector vortex beams, which have been mainly ignored in the literature. When raindrops have a diameter of 6 mm and fog particles have a radius of 0.5 upmum, the signals can reach 152 km and 160 km, respectively. Since these distances are comparable, this work sheds light into the feasibility of implementing measurement device-independent quantum key distribution using vector vortex modes under diverse weather conditions. Most significantly, this opens the door to practical secure quantum communications.

Asymmetric Measurement-Device-Independent Quantum Key Distribution through Advantage Distillation.

Measurement-device-independent quantum key distribution (MDI-QKD) completely closes the security loopholes caused by the imperfection of devices at the detection terminal. Commonly, a symmetric MDI-QKD model is widely used in simulations and experiments. This scenario is far from a real quantum network, where the losses of channels connecting each user are quite different. To adapt such a feature, an asymmetric MDI-QKD model is proposed. How to improve the performance of asymmetric MDI-QKD also becomes an important research direction. In this work, an advantage distillation (AD) method is applied to further improve the performance of asymmetric MDI-QKD without changing the original system structure. Simulation results show that the AD method can improve the secret key rate and transmission distance, especially in the highly asymmetric cases. Therefore, this scheme will greatly promote the development of future MDI-QKD networks.

Measurement-device-independenization of quantum key distribution protocols

Quantum key distribution (QKD) allows the legitimate partner to establish a secret key whose security only depends on physical laws. In recent years, research on QKD by employing insecure measurement devices, namely measurement-device-independent QKD (MDI-QKD) is increased. MDI-QKD removes all attacks on measurement devices and thus an untrusted third party can be employed for measuring. However, a weakness of previous MDI-QKD protocols is the need for joint measurements such as Bell measurements whose efficiency is low in practice. On the other hand, can all QKD protocols become measurement-device-independent remains a problem. In this paper, we present a scheme making prepare-measure QKD protocols become MDI-QKD protocols, called ′measurement−device−independenization′, which does not need to employ joint measurements and could be efficiently implemented by weak coherence sources. The protocol might look like the detector-device-independent (DDI) protocols but it is also secure under the Trojan horse attack. To illustrate this, we investigate the photon-number-adding (PNA) attack and present a scheme, called ′photon−number−purification′, which can also be employed to close loopholes for previous protocols such as DDI and plug-and-play ones.

Measurement-Device-Independent Quantum Key Distribution Based on Decoherence-Free Subspaces with Logical Bell State Analyzer.

Measurement-device-independent quantum key distribution (MDI-QKD) enables two legitimate users to generate shared information-theoretic secure keys with immunity to all detector side attacks. However, the original proposal using polarization encoding is sensitive to polarization rotations stemming from birefringence in fibers or misalignment. To overcome this problem, here we propose a robust QKD protocol without detector vulnerabilities based on decoherence-free subspaces using polarization-entangled photon pairs. A logical Bell state analyzer is designed specifically for such encoding. The protocol exploits common parametric down-conversion sources, for which we develop a MDI-decoy-state method, and requires neither complex measurements nor a shared reference frame. We have analyzed the practical security in detail and presented a numerical simulation under various parameter regimes, showing the feasibility of the logical Bell state analyzer along with the potential that double communication distance can be achieved without a shared reference frame.

Advantages of Asynchronous Measurement-Device-Independent Quantum Key Distribution in Intercity Networks

The new variant of measurement-device-independent quantum key distribution (MDI-QKD), called asynchronous MDI-QKD or mode-pairing MDI-QKD, offers similar repeater-like rate-loss scaling but has the advantage of simple technology implementation by exploiting an innovative post-measurement pairing technique. We herein present an evaluation of the practical aspects of decoy-state asynchronous MDI-QKD. To determine its effectiveness, we analyze the optimal method of decoy-state calculation and examine the impact of asymmetrical channels and multi-user networks. Our simulations show that, under realistic conditions, aynchronous MDI-QKD can furnish the highest key rate with MDI security as compared to other QKD protocols over distances ranging from 50 km to 480 km. At fiber distances of 50 km and 100 km, the key rates attain 6.02 Mbps and 2.29 Mbps respectively, which are sufficient to facilitate real-time one-time-pad video encryption. Our findings indicate that experimental implementation of asynchronous MDI-QKD in intercity networks can be both practical and efficient.

Hacking measurement-device-independent quantum key distribution

Decoy-state measurement-device-independent quantum key distribution (MDI-QKD) is regarded as one of the most promising protocols since it is physically immune to all fatal detection-side attacks. However, the loopholes in the source side still open side channels to eavesdroppers. Previous work has indicated that a system is insecure if its decoy-state modulation is inaccurate, but a practical method for Eve to exploit the inaccurate modulation is still absent. In this work, we propose a practical hacking method and provide a detailed theoretical analysis. Using our method, we experimentally hacked a MDI-QKD system and successfully obtained all final keys. By demonstrating the hacking experiment, we hope to bring attention to source-side security and provide inspiration for the development of protocols with better source-side security.

Cost-Optimization-Based Quantum Key Distribution over Quantum Key Pool Optical Networks

The Measurement-Device-Independent-Quantum Key Distribution (MDI-QKD) has the advantage of extending the secure transmission distances. The MDI-QKD combined with the Hybrid-Trusted and Untrusted Relay (HTUR) is used to deploy large-scale QKD networks, which effectively saves deployment cost. We propose an improved scheme for the QKD network architecture and cost analysis, which simplifies the number of QKD transmitters and incorporates the quantum key pool (QKP) in the QKD network. We developed a novel Hybrid-QKD-Network-Cost (HQNC) heuristic algorithm to solve the cost optimization problem. Simulations verified that the scheme in this paper could save the cost by over 50 percent and 90 percent, respectively.

Analysis of the Effects of the Two-Photon Temporal Distinguishability on Measurement-Device-Independent Quantum Key Distribution

Measurement-device-independent quantum key distribution (MDI-QKD) protects legitimate users from attacks on measurement devices. The decoy method allows for unconditionally secure quantum key generation using lasers. One of the most important issues in MDI-QKD is that photons from two independent lasers must be indistinguishable. Because Alice and Bob send Charlie laser pulses through separate fiber links, the arrival times of the pulses fluctuate independently. According to the Hong-Ou-Mandel (HOM) interference at Charlie's relay, the time delay between two photons has the greatest effect on distinguishability. However, to date, these effects have not been analyzed. Our study uses simulations to investigate the effects of two-photon temporal distinguishability in terms of the visibility of the HOM-dip of two photons on the final key rate of finite-size MDI-QKD. Furthermore, an acceptable time delay range was estimated based on photons with Gaussian spectral amplitude functions.

Multiparty blind quantum computation protocol with deterministic mutual identity authentication

Blind quantum computation (BQC) studies the problem of how a client with limited quantum computation power delegates a computing task to a quantum server while keeping his input, output and algorithm private. To resist attacks from the lack of identity authentication in BQC protocols, we propose a multiparty BQC protocol with deterministic mutual identity authentication. For concreteness, a variant of measurement-device-independent quantum key distribution (MDI-QKD) is first presented, and based on this, a method of deterministically generating the authentication keys of the registered client and the designated server is presented in the registration phase. Then a deterministic mutual identity authentication protocol is proposed to authenticate the identities of the registered client and the designated server by using the variant of MDI-QKD. Finally, in the blind quantum computation phase, the registered client can delegate a computing task to the designated server. Compared with existing BQC protocols with mutual identity authentication, our proposal works in a deterministic and efficient way. Furthermore, the proposed mutual identity authentication method can be applied in other quantum cryptography protocols, thus providing a valuable way for the construction of multiparty quantum communication protocols with identity authentication.

Numerical simulation of quantum key distribution network based on wavelength division multiplexing technology

Wavelength division multiplexing (WDM) technology can improve the networking level and overcome the shortcomings of low key rate under the existing technic background of measurement device independent quantum key distribution (MDI-QKD) protocol application. reference frame independent quantum key distribution (RFI-MDI-QKD) protocol cut down on the influence of the reference frame drift on the key distribution system. The decoy state protocol has important development prospects in the development of quantum communication networking. Combining the advantages of of the above protocols to realize RFI-MDI-QKD with WDM, the results show that the key distribution efficiency is improved with the increase in the number of WDM multiplexed channels, which promotes the further exploration and achievement of QKD networking application.

Security research on practical measurement-device-independent quantum key distribution

The ideal measurement-device-independent quantum key distribution (MDI-QKD), which is immune to all detector side-channel attacks, is built on the Bell state measurement of two single-photon states. However, in practical MDI-QKD where phase-randomized weak coherent pulses (PR-WCPs) are used, the mismatch between states preparation and measurement in X basis leads to the bit error rate of more than 25%, which poses a challenge to the security of QKD. In this paper, we provide a security analysis of practical MDI-QKD based on polarization coding. We analyze the Hong-Ou-Mandel interference of PR-WCPs and Poisson-distributed photon number states (PNs), and find that these two sources are equivalent in MDI-QKD. The security analysis based on entanglement distillation is carried out on PNs, and the measurement results in Z basis and X basis are averaged to overcome the noncorrelation of the error rates in these two bases. Compared with GLLP scheme, a tighter key rate is obtained in this work, and the key rate deviates from the linear key rate bound in a short distance due to the finite proportion of multiphoton terms.

Cryptanalysis and improvement of the measurement-device-independent quantum key distribution with hyper-encoding

Recently, Cui et al. [Sci. China Phys. 62, 110311 (2019)] proposed a measurement-device-independent quantum key distribution (MDI-QKD) scheme based on high-dimensional encoding to increase the channel capacity of each individual photon. A secret key is shared among two legitimate parties via the help of a dishonest third-party (TP). They claimed that the proposed protocol can improve the drawback of the low-key generation rate that existed in the past MDI-QKD schemes. However, this study pointed out a loophole during the security check of TP. That is, the two legitimate participants merely use the corresponding qubit pairs that are both generated in the diagonal basis for the discussion, which leads to a potential attack that not only allows TP to avoid the security check but also creates partial inconsistency of key bits for both communicating sides. Fortunately, this problem can be fixed by a minor correction of the protocol.

Detecting a Photon-Number Splitting Attack in Decoy-State Measurement-Device-Independent Quantum Key Distribution via Statistical Hypothesis Testing.

Measurement-device-independent quantum key distribution (MDI-QKD) is innately immune to all detection-side attacks. Due to the limitations of technology, most MDI-QKD protocols use weak coherent photon sources (WCPs), which may suffer from a photon-number splitting (PNS) attack from eavesdroppers. Therefore, the existing MDI-QKD protocols also need the decoy-state method, which can resist PNS attacks very well. However, the existing decoy-state methods do not attend to the existence of PNS attacks, and the secure keys are only generated by single-photon components. In fact, multiphoton pulses can also form secure keys if we can confirm that there is no PNS attack. For simplicity, we only analyze the weaker version of a PNS attack in which a legitimate user’s pulse count rate changes significantly after the attack. In this paper, under the null hypothesis of no PNS attack, we first determine whether there is an attack or not by retrieving the missing information of the existing decoy-state MDI-QKD protocols via statistical hypothesis testing, extract a normal distribution statistic, and provide a detection method and the corresponding Type I error probability. If the result is judged to be an attack, we use the existing decoy-state method to estimate the secure key rate. Otherwise, all pulses with the same basis leading to successful Bell state measurement (BSM) events including both single-photon pulses and multiphoton pulses can be used to generate secure keys, and we give the formula of the secure key rate in this case. Finally, based on actual experimental data from other literature, the associated experimental results (e.g., the significance level is 5%) show the correctness of our method.

Unbalanced-basis-misalignment-tolerant measurement-device-independent quantum key distribution

Measurement-device-independent quantum key distribution (MDIQKD) is a revolutionary protocol since it is physically immune to all attacks on the detection side. However, the protocol still keeps the strict assumptions on the source side that specify that the four BB84 states must be perfectly prepared to ensure security. Some protocols release part of the assumptions in the encoding system to keep the practical security, but the performance would be dramatically reduced. In this work, we present a MDIQKD protocol that requires less knowledge of the encoding system to combat the troublesome modulation errors and fluctuations. We have also experimentally demonstrated the protocol. The result indicates a high performance and good security for practical applications. Its robustness and flexibility also exhibit a good value for complex scenarios such as the QKD networks.

Afterpulse effect in measurement-device-independent quantum key distribution.

There is no doubt that measurement-device-independent quantum key distribution (MDI-QKD) is a crucial protocol that is immune to all possible detector side channel attacks. In the preparation phase, a simulation model is usually employed to get a set of optimized parameters, which is utilized for getting a higher secure key rate in reality. With the implementation of high-speed QKD, the afterpulse effect which is an intrinsic characteristic of the single-photon avalanche photodiode is no longer ignorable, this will lead to a great deviation compared with the existing analytical model. Here we develop an afterpulse-compatible MDI-QKD model to get the optimized parameters. Our results indicate that by using our afterpulse-compatible model, we can get a much higher key rate than the prior afterpulse-omitted model. It is significant to take the afterpulse effect into consideration because of the improvement of the system working frequency.

Deployed measurement-device independent quantum key distribution and Bell-state measurements coexisting with standard internet data and networking equipment

The forthcoming quantum Internet is poised to allow new applications not possible with the conventional Internet. The ability for both quantum and conventional networking equipment to coexist on the same fiber network would facilitate the deployment and adoption of coming quantum technology. Most quantum networking tasks, like quantum repeaters and the connection of quantum processors, require nodes for multi-qubit quantum measurements (often Bell-State measurements), and their real-world coexistence with the conventional Internet has yet to be shown. Here we field deploy a Measurement-Device Independent Quantum Key Distribution (MDI-QKD) system, containing a Bell-State measurement node, over the same fiber connection as multiple standard Internet Protocol (IP) data networks, between three nearby cities in the Netherlands. We demonstrate over 10 Gb/s classical data communication rates simultaneously with our next-generation QKD system, and estimate 200 GB/s of classical data transmission would be easily achievable without significantly affecting QKD performance. Moreover, as the system ran autonomously for two weeks, this shows an important step towards the coexistence and integration of quantum networking into the existing telecommunication infrastructure.

Design of a multi-channel high-resolution TDC based on FPGA

High-resolution multi-channel time-to-digital converters (TDC) is an important tool in many physical experiments. In the HL-2A tokamak device,a real-time double-ring neutron time-of-flight (TOFII) spectrometer system used to measure the neutron energy spectrum requires the TDC to have a measurement accuracy of 100 ps and a number of 90 channels. In the measurement-device-independent quantum key distribution (MDI-QKD) system, multi-channel and high-precision TDC is also one of the key factors affecting the final bit rate. In this paper, we propose the field programmable gate array (FPGA) method to develop the TDC. By using the coarse-fine combined measurement method, we complete the TDC design through the tapped delay line formed by the internal carry chain of the FPGA. Our method achieves a time measurement of 90 channels and a time resolution of 52 ps.

Measurement-device-independent quantum key distribution protocol with phase post-selection

Measurement-device-independent quantum key distribution (MDI-QKD) protocol can remove all the loopholes of the detection devices and, thus, has attracted much attention. Based on the technique of single-photon interference, we propose a modified MDI-QKD protocol with phase post-selection. We prove the security of the announcement of the private phases in the X basis and show how to apply the phase post-selection method to the double-scanning four-intensity MDI-QKD protocol. The numerical results show that the phase post-selection method can significantly improve the key rates at all distances. In the double-scanning method, two parameters need to be scanned in the calculation of the final key rate, and the global parameter optimization is pretty time-consuming. We propose an accelerated method that can greatly reduce the running time of the global parameter optimization program. This makes the method practically useful in an unstable channel.