On the implementation of a deterministic secure coding protocol using polarization entangled photons

We demonstrate a prototype-implementation of deterministic information encoding for quantum key distribution (QKD) following the ping-pong coding protocol [K. Boström, T. Felbinger, Phys. Rev. Lett. 89 (2002) 187902-1]. Due to the deterministic nature of this protocol the need for post-processing the key is distinctly reduced compared to non-deterministic protocols. In the course of our implementation we analyze the practicability of the protocol and discuss some security aspects of information transfer in such a deterministic scheme.     

安全传送明文的量子直传实验方案设计

乒乓直传协议是一种新颖的量子直传通信协议。基于量子纠缠特性,乒乓协议允许绝对安全地进行明文直接通信和渐进地进行密钥安全分发。是一种绝对安全的即时通信协议。该量子直传协议将来有望成为安全稳定的光量子通信的主流方式。然而,目前还没有该协议的物理实现方案。分析了乒乓直传协议的工作原理．给出了该协议的流程图,进而分析了协议的物理实现机制,结合纠缠光子源、自由空间单光子路由控制和单光子检测技术,提出了在自由空间中实现乒乓直传协议的实验技术方案,并设计出了乒乓直传协议的实验装置。此实验技术方案为从实验角度进一步研究乒乓协议,以及未来此协议的商业化应用提供了参考。     

Deterministic Quantum Key Distribution Using Two Non-orthogonal Entangled States

A deterministic quantum key distribution scheme using two non-orthogonal entangled states is proposed.In the proposed scheme,communicators share key information by exchanging one travelling photon with two random and secret polarization angles.The security of the distributed key is guaranteed by three checking phases in three-way channel and the communicators' secret polarization angles.     

量子直接通信

量子直接通信是量子通信中的一个重要分支, 它是一种不需要事先建立密钥而直接传输机密信息的新型通信模式. 本综述将介绍量子直接通信的基本原理, 回顾量子直接通信的发展历程, 从最早的高效量子直接通信协议、两步量子直接通信模型、量子一次一密直接通信模型等, 到抗噪声的量子直接通信模型以及基于单光子多自由度量子态及超纠缠态的量子直接通信模型, 最后介绍量子直接通信的研究现状并展望其发展未来.     

Performance improvement of unidimensional continuous-variable quantum key distribution using heralded hybrid linear amplifier

We propose an improved scheme for unidimensional continuous-variable quantum key distribution (UCVQKD) using heralded hybrid linear amplifier, aiming to simplify the implementation and improve secret key rate. Different from the symmetrical continuous-variable quantum key distribution protocol (CVQKD), this scheme modulates one quadrature of the coherent state with security insurance. The heralded hybrid linear amplifier concatenates a deterministic linear amplifier (DLA) and a noiseless linear amplifier (NLA), which can tune between the high-gain or high noise-reduction for performance enhancement. Security analysis shows that the proposed scheme can be secured under the collective attacks. Compared with traditional UCVQKD involving noiseless amplifier, the security transmission distance of proposed protocol is increased by 24 kilometers. It not only simplifies the modulation process but also has approximate performance with symmetrical CVQKD in terms of maximal security transmission distance.     

Performance optimization for quantum key distribution in lossy channel using entangled photons

In quantum key distribution(QKD), the times of arrival of single photons are important for the keys extraction and time synchronization. The time-of-arrival(TOA) accuracy can affect the quantum bit error rate(QBER) and the final key rate. To achieve a higher accuracy and a better QKD performance, different from designing more complicated hardware circuits, we present a scheme that uses the mean TOA of M frequency-entangled photons to replace the TOA of a single photon. Moreover, to address the problem that the entanglement property is usually sensitive to the photon loss in practice,we further propose two schemes, which adopt partially entangled photons and grouping-entangled photons, respectively.In addition, we compare the effects of these three alternative schemes on the QKD performance and discuss the selection strategy for the optimal scheme in detail. The simulation results show that the proposed schemes can improve the QKD performance compared to the conventional single-photon scheme obviously, which demonstrate the effectiveness of the proposed schemes.     

Traceable Scheme of Public Key Encryption with Equality Test

Public key encryption supporting equality test (PKEwET) schemes, because of their special function, have good applications in many fields, such as in cloud computing services, blockchain, and the Internet of Things. The original PKEwET has no authorization function. Subsequently, many PKEwET schemes have been proposed with the ability to perform authorization against various application scenarios. However, these schemes are incapable of traceability to the ciphertexts. In this paper, the ability of tracing to the ciphertexts is introduced into a PKEwET scheme. For the ciphertexts, the presented scheme supports not only the equality test, but also has the function of traceability. Meanwhile, the security of the proposed scheme is revealed by a game between an adversary and a simulator, and it achieves a desirable level of security. Depending on the attacker’s privileges, it can resist OW-CCA security against an adversary with a trapdoor, and can resist IND-CCA security against an adversary without a trapdoor. Finally, the performance of the presented scheme is discussed.     

Eavesdropping on the "ping-pong" quantum communication protocol

Security of the "ping-pong" quantum communication protocol recently proposed by Bostr?m and Felbinger [Phys. Rev. Lett. 89, 187902 (2002)]] is analyzed in the case of considerable quantum channel losses. The eavesdropping scheme is presented, which reveals that the ping-pong protocol is not secure for transmission efficiencies lower than 60%. Our scheme induces 50% losses, which, however, can be hidden in the channel losses if one replaces the original lossy channel with a less lossy one. Finally, a possible improvement of the ping-pong protocol security is proposed.     

Quantum Dense Coding Without Joint Measurement

We propose two schemes for quantum dense coding without Bell states measurement. One is deterministic, the other is probabilistic. In the deterministic scheme, the initial entangled state will be not destructed. In the probabilistic scheme, the initial unknown nonmaximal entangled state will be transformed into a maximalentangled one. Our schemes require two auxiliary particles and perform single-qubit measurements on them. Thus our schemes are simple and economic.     

A new synchronization scheme based on time division multiplexing and wavelength division multiplexing technology for practical quantum key distribution system

Three clock synchronization schemes for a quantum key distribution system are compared experimentally through the outdoor fibre and the interaction physical model of the the clock signal and the the quantum signal in the quantum key distribution system is analysed to propose a new synchronization scheme based on time division multiplexing and wavelength division multiplexing technology to reduce quantum bits error rates under some transmission rate conditions.The proposed synchronization scheme can not only completely eliminate noise photons from the bright background light of the the clock signal,but also suppress the fibre nonlinear crosstalk.     

Quantum identity authentication based on ping-pong technique for photons

To prevent active attack, an one-way quantum identity authentication scheme is proposed by employing mechanism of ping-pong protocol and property of quantum controlled-NOT gate. It can verify the user's identity as well as distribute an updated key as the authentication key. Analytical results show the proposed scheme is secure under general individual attack.     

基于超纠缠交换的量子密钥分发

给出一种基于超纠缠交换的量子密钥分发方案，这个方案可以同时产生确定密钥和随机密钥，并且它的安全性不受任何损害.这个方案只需要一对在空间(路径)模式和极化模式上超纠缠的光子就能获得4 bit的密钥(2 bit随机密钥和2 bit确定密钥).在目前的实验条件下，这个方案可以通过线性光学来实现. 关键词： 量子密钥分发 超纠缠 线性光学     

基于量子远程通信的连续变量量子确定性密钥分配协议

基于量子远程通信的原理, 本文借助双模压缩真空态和相干态, 提出一种连续变量量子确定性密钥分配协议. 在利用零差探测法的情况下协议的传输效率达到了100%. 从信息论的角度分析了协议的安全性, 结果表明该协议可以安全传送预先确定的密钥. 在密钥管理中, 量子确定性密钥分配协议具有量子随机性密钥分配协议不可替代的重要地位和作用. 与离散变量量子确定性密钥分配协议相比, 该协议分发密钥的速率和效率更高, 又协议中用到的连续变量量子态易于产生和操控、适于远距离传输, 因此该协议更具有实际意义.     

Deterministic Joint Remote Preparation of an Arbitrary Two-Qubit State Using the Cluster State

Recently, deterministic joint remote state preparation (JRSP) schemes have been proposed to achieve 100% success probability. In this paper, we propose a new version of deterministic JRSP scheme of an arbitrary two-qubit state by using the six-qubit cluster state as shared quantum resource. Compared with previous schemes, our scheme has high efficiency since less quantum resource is required, some additional unitary operations and measurements are unnecessary. We point out that the existing two types of deterministic JRSP schemes based on GHZ states and EPR pairs are equivalent.     

Efficient scheme for remote preparation of arbitrary n-qubit equatorial states

Recently,a scheme for deterministic remote preparation of arbitrary multi-qubit equatorial states was proposed by Wei et al.[Quantum Inf.Process.1770(2018)].It is worth mentioning that the construction of mutual orthogonal measurement basis plays a key role in quantum remote state preparation.In this paper,a simple and feasible remote preparation of arbitrary n-qubit equatorial states scheme is proposed.In our scheme,the success probability will reach unit.Moreover,there are no coefficient constraint and auxiliary qubits in this scheme.It means that the success probabilities are independent of the coefficients of the entangled channel.The advantage of our scheme is that the mutual orthogonal measurement basis is devised.To accomplish the quantum remote state preparation(RSP)schemes,some new sets of mutually orthogonal measurement basis are introduced.     

A Novel Deterministic Quantum Communication Scheme Using Stabilizer Quantum Code

Exploiting the encoding process of the stabilizer quantum code [[n, k, d]], a deterministic quantum communication scheme, in which n - 1 photons are distributed forward and backward in two-way channel, is proposed to transmit the secret messages with unconditional security. The present scheme can be implemented to distribute the secret quantum （or classical） messages with great capacity in imperfect quantum channel since the utilized code encodes k-qubit messages for each scheme run.     

Improving continuous-variable quantum key distribution under local oscillator intensity attack using entanglement in the middle

A modified continuous-variable quantum key distribution(CVQKD) protocol is proposed by originating the entangled source from a malicious third party Eve in the middle instead of generating it from the trustworthy Alice or Bob. This method is able to enhance the efficiency of the CVQKD scheme attacked by local oscillator(LO) intensity attack in terms of the generated secret key rate in quantum communication. The other indication of the improvement is that the maximum transmission distance and the maximum loss tolerance can be increased significantly, especially for CVQKD schemes based on homodyne detection.     

Fault tolerant deterministic secure quantum communication using logical Bell states against collective noise

This study proposes two novel fault tolerant deterministic secure quantum communication(DSQC) schemes resistant to collective noise using logical Bell states. Either DSQC scheme is constructed based on a new coding function, which is designed by exploiting the property of the corresponding logical Bell states immune to collective-dephasing noise and collective-rotation noise, respectively. The secret message can be encoded by two simple unitary operations and decoded by merely performing Bell measurements, which can make the proposed scheme more convenient in practical applications.Moreover, the strategy of one-step quanta transmission, together with the technique of decoy logical qubits checking not only reduces the influence of other noise existing in a quantum channel, but also guarantees the security of the communication between two legitimate users. The final analysis shows that the proposed schemes are feasible and robust against various well-known attacks over the collective noise channel.     

自动补偿高效的差分相位编码QKD系统

提出一种自动补偿高效实用的改进型差分相位编码量子密钥分发方案.在Alice端采用偏振型强度调制器对连续激光进行调制，产生任意个相干脉冲进行差分相位调制编码；在Bob端采用双FM干涉仪代替传统的M-Z干涉仪，自动补偿了环境引起的偏振抖动，提高了系统的干涉稳定度.简化了系统的结构，提高了密钥生成效率，增强了系统的安全性.在实验上实现了稳定的80km量子密钥分配，误码率<4%. 关键词： 量子保密通信 量子密钥分发 差分相位编码 偏振型强度调制器     

Arbitrated quantum signature scheme based on reusable key

An arbitrated quantum signature scheme without using entangled states is proposed.In the scheme,by employing a classical hash function and random numbers,the secret keys of signer and receiver can be reused.It is shown that the proposed scheme is secure against several well-known attacks.Specifically,it can stand against the receiver’s disavowal attack.Moreover,compared with previous relevant arbitrated quantum signature schemes,the scheme proposed has the advantage of less transmission complexity.