Round-robin differential-phase-shift quantum key distribution with heralded pair-coherent sources

Round-robin differential-phase-shift (RRDPS) quantum key distribution (QKD) scheme provides an effective way to overcome the signal disturbance from the transmission process. However, most RRDPS-QKD schemes use weak coherent pulses (WCPs) as the replacement of the perfect single-photon source. Considering the heralded pair-coherent source (HPCS) can efficiently remove the shortcomings of WCPs, we propose a RRDPS-QKD scheme with HPCS in this paper. Both infinite-intensity decoy-state method and practical three-intensity decoy-state method are adopted to discuss the tight bound of the key rate of the proposed scheme. The results show that HPCS is a better candidate for the replacement of the perfect single-photon source, and both the key rate and the transmission distance are greatly increased in comparison with those results with WCPs when the length of the pulse trains is small. Simultaneously, the performance of the proposed scheme using three-intensity decoy states is close to that result using infinite-intensity decoy states when the length of pulse trains is small.     

On four-photon entanglement from parametric down-conversion process

We propose a scheme to generate a family of four-photon polarization-entangled states from the second-order emission of the spontaneous parametric down-conversion (PDC) process. Based on linear optical elements and the coincidence detection, the four indistinguishable photons emitted from PDC source result in the family of states which are so different from the previous. By tuning the orientation of wave plate, we are able to obtain the well-known four-photon Greenberger–Horne–Zeilinger (GHZ) state, superposition of two (three) orthogonal GHZ states and generic superposition of four orthogonal GHZ states. As an application, we analyze quantum nonlocality for the present superposition states. Under particular phase settings, we calculate the local hidden variable (LHV) correlation and the quantum correlation function. As a result, the Bell inequality derived from the LHV correlation is completely violated by these four-photon entangled states. The maximal quantum violation occurs naturally with the four-photon GHZ state, and there exist the quantum violations which are larger than previously reported values over a surprisingly wide range. It means that the present four-photon entangled states are therefore suitable for testing the LHV theory.     

基于Cluster态的可验证多方量子密钥协商方案

基于四量子比特Cluster态,提出一种可验证多方量子密钥协商方案.方案允许每次由两个参与者利用自己的子密钥分别在每个四量子比特Cluster态的两个粒子上执行X运算,并对转换后的Cluster态执行延迟测量,这保证了每个参与者对协商密钥的贡献相等.提出的方案使用相互无偏基粒子作为诱饵粒子,并且利用对称二元多项式的一对函数值对这些诱饵粒子执行酉运算,不仅可以进行窃听检验,而且还能进行参与者之间的身份验证.本方案适用于任意大于2的参与者人数.安全性分析表明,提出的方案能够抵抗外部攻击及参与者攻击.与现有的多方密钥协商方案相比,该方案不仅在诱饵粒子的使用上有优势,同时具有较高的量子比特效率.     

Multiparty quantum key agreement protocol based on locally indistinguishable orthogonal product states

Based on locally indistinguishable orthogonal product states, we propose a novel multiparty quantum key agreement (QKA) protocol. In this protocol, the private key information of each party is encoded as some orthogonal product states that cannot be perfectly distinguished by local operations and classical communications. To ensure the security of the protocol with small amount of decoy particles, the different particles of each product state are transmitted separately. This protocol not only can make each participant fairly negotiate a shared key, but also can avoid information leakage in the maximum extent. We give a detailed security proof of this protocol. From comparison result with the existing QKA protocols, we can know that the new protocol is more efficient.     

An arbitrated quantum signature scheme with fast signing and verifying

Existing arbitrated quantum signature (AQS) schemes are almost all based on the Leung quantum one-time pad (L-QOTP) algorithm. In these schemes, the receiver can achieve an existential forgery of the sender’s signatures under the known message attack, and the sender can successfully disavow any of her/his signatures by a simple attack. In this paper, a solution of solving the problems is given, through designing a new QOTP algorithm relying largely on inserting decoy states into fixed insertion positions. Furthermore, we present an AQS scheme with fast signing and verifying, which is based on the new QOTP algorithm. It is just using single particle states and is unconditional secure. To fulfill the functions of AQS schemes, our scheme needs a significantly lower computational costs than that required by other AQS schemes based on the L-QOTP algorithm.     

Protecting single-photon entanglement with practical entanglement source

Single-photon entanglement (SPE) is important for quantum communication and quantum information processing. However, SPE is sensitive to photon loss. In this paper, we discuss a linear optical amplification protocol for protecting SPE. Different from the previous protocols, we exploit the practical spontaneous parametric down-conversion (SPDC) source to realize the amplification, for the ideal entanglement source is unavailable in current quantum technology. Moreover, we prove that the amplification using the entanglement generated from SPDC source as auxiliary is better than the amplification assisted with single photons. The reason is that the vacuum state from SPDC source will not affect the amplification, so that it can be eliminated automatically. This protocol may be useful in future long-distance quantum communications.     

基于团簇态的量子秘密共享方案

提出了一个基于团簇态的量子秘密共享方案,发送者通过Pauli操作将经典秘密信息编码在团簇态上进行分发,接收者通过联合测量实现秘密共享。协议插入EPR对作为诱骗态以防止窃听,通过安全性分析证明本协议是安全的,可以抵抗截获-测量、截获-重发和纠缠-测量攻击。此外,协议传输一个四粒子团簇态可以共享四个经典比特信息,量子比特效率达到100%。     

Adaptive ILC for a class of discrete-time systems with iteration-varying trajectory and random initial condition

In this work we present a discrete-time adaptive iterative learning control (AILC) scheme to deal with systems with time-varying parametric uncertainties. Using the analogy between the discrete-time axis and the iterative learning axis, the new adaptive ILC can incorporate a Recursive Least Squares (RLS) algorithm, hence the learning gain can be tuned iteratively along the learning axis and pointwisely along the time axis. When the initial states are random and the reference trajectory is iteration-varying, the new AILC can achieve the pointwise convergence over a finite time interval asymptotically along the iterative learning axis.     

Measurement device-independent quantum key distribution with heralded pair coherent state

The original measurement device-independent quantum key distribution is reviewed, and a modified protocol using heralded pair coherent state (HPCS) is proposed to overcome the quantum bit error rate associated with the dark count rate of the detectors in long-distance quantum key distribution. Our simulation indicates that the secure transmission distance can be improved evidently with HPCS owing to the lower probability of vacuum events when compared with weak coherent source scenario, while the secure key rate can be increased with HPCS due to the higher probability of single-photon events when compared with heralded single-photon source scenario. Furthermore, we apply the finite key analysis to the decoy state MDI-QKD with HPCS and obtain a practical key rate.     

基于Bell态的量子秘密共享协议

为提高效率,提出了一种直接共享经典信息的量子秘密共享协议。协议利用Pauli矩阵的特殊性质将经典信息编码在Bell态上实现秘密共享,为了检测是否存在窃听者,通过随机插入诱骗光子的方法确保传输的安全。分析表明该协议是安全的,效率可以达到1个Be11态共享2 bit经典信息。     

Design of a high-repetition rate photon source in a quantum key distribution system

Photon source with high-repetition quantum message transmission is needed in the quantum key distribution (QKD) system for long distance and high-repetition rate. We design high-repetition-rate weak coherent light by applying a practical QKD system with decoy states and polarization coding including an FPGA-based true random number generator, narrow pulse shaping under the modulation of high-speed true random number as well as its laser driver. The test indicates that the repetition rate of such light can attain a high performance of 650 MHz, pulse width less than 300 ps, stability of pulse amplitude better than 5%, and extinction rate better than 1000:1.     

有源诱饵抗反辐射导弹方法研究

文章以研究有源诱饵抗反辐射导弹ARM(anti-radiation missile)的有效方法为目的,从有源诱饵诱偏ARM的基本原理出发,讨论了有源诱饵有效对抗ARM的布站方法,对几种典型布局的三点源和四点源诱偏系统的诱偏效果用软件进行了模拟仿真,并进一步对诱偏系统中某诱饵故障时的诱偏效果进行了仿真和分析;经过对比和分析,得到了三点源和四点源诱偏系统的较理想的布站方案;文中还对实际配置的诱饵系统存在高度差的情况进行了讨论和分析;分析表明,诱偏系统进行合理的布局和高度差安排,能够得到更有效的诱偏效果。     

A dynamic multiparty quantum direct secret sharing based on generalized GHZ states

This paper proposes a new dynamic multiparty quantum direct secret sharing (DQDSS) using mutually unbiased measurements based on generalized GHZ states. Without any unitary operations, an agent can obtain a shadow of the secret by simply performing a measurement on single photons. In the proposed scheme, multiple agents can be added or deleted and the shared secret need not be changed. Our DQDSS scheme has several advantages. The dealer is not required to retain any photons and can further share a predetermined key instead of a random key to the agents. Agents can update their shadows periodically, and the dealer does not need to be online. Furthermore, the proposed scheme can resist not only the existing attacks, but also cheating attacks from dishonest agents. Hence, compared to some famous DQSS schemes, the proposed scheme is more efficient and more practical. Finally, we establish a mathematical model about the efficiency and security of the scheme and perform simulation analyses with different parameters using MATLAB.     

Arbitrated quantum signature scheme based on cluster states

Cluster states can be exploited for some tasks such as topological one-way computation, quantum error correction, teleportation and dense coding. In this paper, we investigate and propose an arbitrated quantum signature scheme with cluster states. The cluster states are used for quantum key distribution and quantum signature. The proposed scheme can achieve an efficiency of 100 %. Finally, we also discuss its security against various attacks.     

The enhanced measurement-device-independent quantum key distribution with two-intensity decoy states

We put forward a new scheme for implementing the measurement-device-independent quantum key distribution (QKD) with weak coherent source, while using only two different intensities. In the new scheme, we insert a beam splitter and a local detector at both Alice’s and Bob’s side, and then all the triggering and non-triggering signals could be employed to process parameter estimations, resulting in very precise estimations for the two-single-photon contributions. Besides, we compare its behavior with two other often used methods, i.e., the conventional standard three-intensity decoy-state measurement-device-independent QKD and the passive measurement-device-independent QKD. Through numerical simulations, we demonstrate that our new approach can exhibit outstanding characteristics not only in the secure transmission distance, but also in the final key generation rate.     

基于可重用的不对称三粒子纠缠态的量子秘密共享

本方案利用可重用的不对称三粒子纠缠态作为载体,发送方用控制非门操作将信息编码到载体上,接收方再利用控制非门操作解除纠缠,实现量子秘密共享。为了检测是否有窃听者,通过随机插入诱骗粒子的方法作窃听检测,随后进行二次检测窃听,使其安全性具有双重保证。分析表明方案能有效防止窃听,抵御纠缠欺骗攻击。     

A VSS identification scheme for time-varying parameters

Based on variable structure system theory and sliding mode, we develop an identification scheme suitable for time-varying parameters. The new identification scheme, working in closed-loop, addresses several key issues in system identification simultaneously: unstable process, highly nonlinear and uncertain dynamics, fast time varying parameters and rational nonlinear in the parametric space. Other important issues associated with identification, such as the persistent excitation property and insensitivity to measurement noise, are also discussed. A robotic manipulator is used as the illustrative example and the basis for comparison.     

Two-party quantum key agreement with four-qubit cluster states

Based on four-qubit cluster states, we present a two-party quantum key agreement (QKA) scheme using unitary operations. In this scheme, two participants perform the unitary operation on the different photon of the same cluster state, which guarantees that each party contributes equally to the agreement key. By measuring each cluster state and decoding, these two participants can generate a four-bit classical key without the exchange of classical bits between them. Compared with other existed two-party QKA protocols, our scheme is efficient. Security analysis shows that our protocol is secure against both participant and outsider attack.     

Entanglement generation and entanglement concentration of two-photon four-dimensional spatial modes partially entangled Dicke state

Two-photon four-dimensional spatial modes partially entangled Dicke state can be compactly generated from six concurrent spontaneous parametric down-conversion processes by cascading poling domain structures in 5% MgO-doped poled lithium niobate bulk crystal. Entanglement concentration of the two-photon four-dimensional spatial modes partially entangled Dicke state can be realized by using quantum nondestructive detection of nonlinear Kerr medium, optical beam splitter, and quantum gate operation.