Scheme for Robust Long-Distance Continuous Variable Quantum Key Distribution

It is shown that the configuration of phase coding for quantum key distribution with single photon can also be used for continuous variable quantum key distribution. Therefore the robust long-distance high-speed quantum key distribution can be achieved with current technology.     

Application of a Discrete Phase-Randomized Coherent State Source in Round-Robin Differential Phase-Shift Quantum Key Distribution

Recently, a novel kind of quantum key distribution called the round-robin differential phase-shift(RRDPS)protocol was proposed, which bounds the amount of leakage without monitoring signal disturbance. The protocol can be implemented by a weak coherent source. The security of this protocol with a simply characterized source has been proved. The application of a common phase shift can improve the secret key rate of the protocol. In practice, the randomized phase is discrete and the secret key rate is deviated from the continuous case. In this study, we analyze security of the RRDPS protocol with discrete-phase-randomized coherent state source and bound the secret key rate. We fix the length of each packet at 32 and 64, then simulate the secret key rates of the RRDPS protocol with discrete-phase randomization and continuous-phase randomization. Our simulation results show that the performance of the discrete-phase randomization case is close to the continuous counterpart with only a small number of discrete phases. The research is practically valuable for experimental implementation.     

Multi-mode Gaussian Modulated Continuous-Variable Measurement-Device-Independent Quantum Key Distribution

We propose a novel multi-mode Gaussian modulated continuous variable measurement-device-independent quantum key distribution (MDI-CVQKD) protocol where Alice and Bob prepare independent and identically distributed Gaussian modulated coherent states in multiple independent modes respectively along with Charlie using a traditional noise homodyne detector to measure. Since it is completely handed over to an untrusted third party (Charlie) to measure, this protocol can effectively eliminate the defects of the actual detector. As well as, we also proved that the multi-mode MDI-CVQKD protocol can reduce electronic noise. The simulation results show that the multi-mode Gaussian modulated MDI-CVQKD protocol can indeed significantly improve the key rate of the original Gaussian modulated MDI-CVQKD protocol, and extend the maximum secure transmission distance of the secret key.

     

Circular threshold quantum secret sharing

This paper proposes a circular threshold quantum secret sharing （TQSS） scheme with polarized single photons. A polarized single photon sequence runs circularly among any t or more of n parties and any t or more of n parties can reconstruct the secret key when they collaborate. It shows that entanglement is not necessary for quantum secret sharing. Moreover, the theoretic efficiency is improved to approach 100% as the single photons carrying the secret key are deterministically forwarded among any t or more of n parties, and each photon can carry one bit of information without quantum storage. This protocol is feasible with current technology.     

Efficient Multiparty Quantum Secret Sharing of Secure Direct Communication Based on Bell States and Continuous Variable Operations

By using some ordered Bell states as quantum channel, we propose a protocol for multiparty quantum secret sharing of secure direct communication. The present scheme follows the ideas of dense coding and ping-pong technique. It has a high source capacity as each traveling photon carries two bits of classical secret messages, and has a high intrinsic efficiency because almost all the instances are useful. Since the continuous variable operations instead of the discrete unitary operations used usually are employed to realize the sharing controls, the security of the present protocol is therefore enhanced. Furthermore, due to existing multilevel security checking procedures, the present scheme can prevent against some usual attack strategies.     

Improvement on ‘Multiparty Quantum Key Agreement with Four-Qubit Symmetric W State’

Recently, Wang et al. (Int J Theo Phys: pp. 3716–3726, 2018) proposed a multiparty quantum key agreement scheme with four-particles W state. Their protocol uses the delayed measurement technique, the block transmission technique, and the single decoy photon technique to determine a shared secret key between three or more participants. They claimed that their protocol could resist both internal/participant and external attacks. However, this work indicates that two dishonest participants can collude to get the private data of a participant who executes the protocol honestly. To solve this issue, a simple modification is suggested in this work.

     

多方控制的量子安全直接通信协议

基于单光子序列的顺序重排，提出了一种可应用于一些特殊的场景的多方控制的量子安全直接通信协议.协议中，接收方只有在得到所有控制方的同意之后，才能恢复出发送方的秘密消息.协议的安全性由量子不可克隆定理和单光子序列的秘密传输顺序所保证.此外，除了用于窃听检测的部分光子，所有的光子都用于编码秘密消息，而且协议的实现不需要使用纠缠态，该协议具有效率高和实现简单等特点. 关键词： 量子密码 量子安全直接通信 顺序重排 单光子     

Quantum Overloading Cryptography Using Single-Photon Nonlocality

Using the single-photon nonlocality, we propose a quantum novel overloading cryptography scheme, in which a single photon carries two bits information in one-way quantum channel. Two commutative modes of the single photon, the polarization mode and the spatial mode, are used to encode secret information. Strict time windows are set to detect the impersonation attack. The spatial mode which denotes the existence of photons is noncommutative with the phase of the photon, so that our scheme is secure against photon-number-splitting attack. Our protocol may be secure against individual attack.     

Efficient Three-Party Quantum Secret Sharing with Single Photons

A scheme for three-party quantum secret sharing of a private key is presented with single photons. The agent Bob first prepares a sequence of single photons with two biased bases and then sends them to the boss Alice who checks the security of the transmission with measurements and produces some decoy photons by rearranging the orders of some sample photons. Alice encodes her bits with two unitary operations on the photons and then sends them to the other agent. The security of this scheme is equivalent to that in the modified Bennett Brassard 1984 quantum key distribution protocol. Moreover, each photon can carry one bit of the private key and the intrinsic efficiency for qubits and the total efficiency both approach the maximal value 100% when the number of the bits in the key is very large.     

Scalable Quantum Secret Sharing Extended from Quantum Key Distribution

We suggest a general approach for extending quantum key distribution （Q, KD） protocols possessing discrete rotational symmetry into quantum secret sharing （QSS） schemes among multiparty, under certain conditions. Only local unitary operations are required for this generalization based on the almost mature technologies of Q, KD. Theoretically, the number of the participating partners can be arbitrary high. As an application of this method, we propose a fault-tolerant QSS protocol based on a fault-tolerant QKD implementation. The 6-state protocol is also discussed.     

连续变量量子密码术

文章综述了连续变量量子密码术的基本原理，突出了其在光源制备、光子探测以及量子密钥生成的码率等办面相对于单光子量子密码术的优越性，给出了连续变量量子密码术的安全性以及对线路噪声的具体要求，提出了连续变量量子密码术目前所面临的主要困难和今后的发展前景。     

Robust Multiparty Quantum Secret Key Sharing Over Two Collective-Noise Channels via Three-Photon Mixed States

We present a robust （n, n）-threshold scheme for multiparty quantum secret sharing of key over two collectivenoise channels （i.e., the collective dephasing channel and the collective rotating channel） via three-photon mixed states, In our scheme, only if all the sharers collaborate together can they establish a joint key with the message sender and extract the secret message from the sender＇s encrypted message. This scheme can be implemented using only a Bell singlet, a one-qubit state and polarization identification of single photon, so it is completely feasible according to the present-day technique.     

High-Capacity Three-Party Quantum Secret Sharing with Single Photons in Both the Polarization and the Spatial-Mode Degrees of Freedom

We present a high-capacity three-party quantum secret sharing (QSS) protocol with a sequence of single photons in both the polarization and the spatial-mode degrees of freedom. By inserting the boss Alice into the middle position between the two agents Bob and Charlie, our QSS protocol is secure in theory. The boss Alice chooses some unitary operations to encode her information on the single photons. It is interesting to point out the fact that Alice does not change the bases of the single photons which are used to carry the useful information about the private key, which improves its success probability for obtaining a private key. Compared with the QSS protocol by Zhou et al. (Chin. Phys. Lett. 24, 2181 (2007)), our QSS protocol has a higher capacity without increasing the difficulty of its implementation in experiment as each correlated photon can carry two bits of useful information. Compared with those QSS protocols based on entangled photon pairs and Bell-state measurements, our QSS protocol is more feasible as it does not require the complete Bell-state analysis which is not easy with linear optics. We give out the setup for the implementation of our QSS protocol with linear optical elements.     

Implementation of High Capacity Quantum Secret Sharing Using Orbital Angular Momentum of Photons

Employing orbital angular momentum (OAM) of single photon, we demonstrate a high dimensional quantum secret sharing protocol. The protocol shows a high capacity of communication as the keys are encoded on the OAM of photons in d-level Hilbert space. In the proposed protocol, the remote users could share secret keys securely. The implementation for the OAM state preparation and measurement is also discussed. We show that the protocol exhibits a high security and the alignment of shared reference frames is not required.     

Continuous variable quantum key distribution

Quantum key distribution enables unconditionally secure key distribution between two legitimate users.The information-theoretic security is guaranteed by the fundamental laws of quantum physics.Initially,the quantum key distribution protocol was proposed based on the qubits.Later on,it was found that quantum continuous variables can also be exploited for this target.The continuous variable quantum key distribution can build upon standard telecommunication technology and exhibits a higher secret key rate per pulse at a relatively short distance due to the possibility of encoding more than 1 bit per pulse.In this article,we review the current status of the continuous variable quantum key distribution research,including its basic principle,experimental implementations,security and future directions;the experimental progress in this field made by our group is also presented.     

Mediated Semi‐Quantum Key Distribution Using Single Photons

A new mediated semi‐quantum key distribution (SQKD) protocol is proposed, allowing two classical participants to share a secret key with the help of an untrusted third party, who only needs to generate single photons and perform Bell measurements. This is the first work attempting to reduce the quantum overhead of the untrusted third party, which makes the mediated SQKD even more practical. The proposed protocol is shown to be free from several well‐known attacks.     

High-capacity Deterministic Secure Four-qubit <Emphasis Type="Italic">W</Emphasis> State Protocol for Quantum Communication Based on Order Rearrangement of Particle Pairs

A novel high-capacity protocol for deterministic secure quantum communication with four-qubit symmetric W state is proposed. In the presented protocol, the secret messages can be encoded on the four-qubit symmetric W states by employing four two-particle unitary operations and directly decoded by utilizing the corresponding measurements in Bell basis or single particle basis. It has a high capacity as each W state can carry two bits of secret information, and has a high intrinsic efficiency because almost all the instances are useful. The security of this communication can be ensured by the decoy photon checking technique and the order rearrangement of particle pairs technique. Furthermore, this protocol is feasible with present-day technique.     

Multi-Party Quantum Key Agreement by an Entangled Six-Qubit State

Since the first quantum key agreement protocol based on Bell state was presented by Zhou et al., much attention has focused on it, which is based on entangled states and product states. In this paper, we propose a multi-party quantum key agreement protocol, in which the genuinely maximally entangled six-qubit states are used. The presented protocol allows participants to share a secret key and preserves the following advantages. First, the outcome of the protocol is influenced by all parties; Second, the presented protocol is fairness, i.e., no one can determine the shared key alone; Third, outside eavesdroppers cannot gain the generated key without introducing any error. The security analysis shows that our protocol can resist both outside attacks and inside attacks.     

Multiparty Quantum Key Agreement Based on Three-Photon Entanglement with Unidirectional Qubit Transmission

A multiparty quantum key agreement protocol based on three-photon entangled states is proposed. In this scheme, the quantum channel between all parties is that of a closed loop, in which the qubit transmission is one-way. Each party can obtain the sum of the other parties’ secret key values through the coding rules instead of extracting their private keys. The shared secret key cannot be determined by any subset of all the participants except the universal set and each party makes an equal contribution to the final key. Moreover, the security analysis shows our protocol can resist both outside attacks and inside attacks.

     

基于Bell态粒子和单光子混合的量子安全直接通信方案的信息泄露问题

最近,一种基于Bell态粒子和单光子混合的量子安全直接通信方案[物理学报65 230301(2016)]被提出.文章宣称一个量子态可以编码3比特经典信息,从而使得协议具有很高的信息传输效率.不幸的是,该协议存在信息泄露问题:编码在单光子上的3比特经典信息有2比特被泄露,而编码在Bell态上的3比特经典信息有1比特被泄露,所以它不是一个安全的直接量子通信方案.在保留原协议思想且尽可能少地更改原协议的基础上,我们提出一种改进的消息编码规则,从而解决信息泄露问题,使之成为一个高效、安全的量子通信协议.衷心希望研究者能对量子安全通信协议中信息泄露问题引起足够重视,设计真正安全的量子通信协议.