Multi-party quantum state sharing of an arbitrary multi-qubit state via \chi -type entangled states

By using the \(\chi \) -type entangled states, a novel scheme for multi-party quantum state sharing (MQSTS) of an arbitrary multi-qubit state is investigated. It is shown that the MQSTS scheme can be faithfully realized by performing appropriate Bell state measurements, Z basis measurements and local unitary operations, rather than multi-qubit entanglement or multi-particle joint measurements. Thus, our MQSTS scheme is more convenient in a practical application than some previous schemes. Furthermore, its intrinsic efficiency for qubits approaches 100 %, and the total efficiency really approaches the maximal value, which is higher than those of the previous MQSTS schemes. Finally, we analyze the security from the views of participant attack and outside attack in detail.     

Multi-party quantum state sharing of an arbitrary two-qubit state with Bell states

We present a new scheme for sharing an arbitrary two-qubit quantum state with n agents. In our scheme, the sender Alice first shares n Einsein-Podolsky-Rosen (EPR) pairs in Bell states with n agents. After setting up the secure quantum channel, Alice first applies (n − 2) Controlled-Not (CNOT) gate operations, and then performs two Bell-state measurements and (n − 2) single-particle measurements (n >2). In addition, all controllers only hold one particle in their hands, respectively, and thus they only need to perform a single-particle measurement on the respective particle with the basis {|0?, |1?}{\{{\vert}0\rangle, {\vert}1\rangle\}}. Compared with other schemes with Bell states, our scheme needs less qubits as the quantum resources and exchanges less classical information, and thus obtains higher total efficiency.     

Multi-party quantum secret sharing with the single-particle quantum state to encode the information

We present a three-party quantum secret sharing (QSS) scheme via the entangled Greenberger–Horne–Zeilinger state. In this scheme, the sender Alice encodes her arbitrary secret information by means of preparing a single-particle quantum state. The agent Bob obtains his shared information according to his hobby, while Charlie can easily calculate his shared information. The proposed scheme is secure. It is shown that even a dishonest agent, who may avoid the security checking, cannot obtain any useful information. Moreover, we further investigate the multi-party QSS scheme which allows most agents to predetermine their information.     

Effect of quantum noise on deterministic remote state preparation of an arbitrary two-particle state via various quantum entangled channels

As one of important research branches of quantum communication, deterministic remote state preparation (DRSP) plays a significant role in quantum network. Quantum noises are prevalent in quantum communication, and it can seriously affect the safety and reliability of quantum communication system. In this paper, we study the effect of quantum noise on deterministic remote state preparation of an arbitrary two-particle state via different quantum channels including the \(\chi \) state, Brown state and GHZ state. Firstly, the output states and fidelities of three DRSP algorithms via different quantum entangled channels in four noisy environments, including amplitude-damping, phase-damping, bit-flip and depolarizing noise, are presented, respectively. And then, the effects of noises on three kinds of preparation algorithms in the same noisy environment are discussed. In final, the theoretical analysis proves that the effect of noise in the process of quantum state preparation is only related to the noise type and the size of noise factor and independent of the different entangled quantum channels. Furthermore, another important conclusion is given that the effect of noise is also independent of how to distribute intermediate particles for implementing DRSP through quantum measurement during the concrete preparation process. These conclusions will be very helpful for improving the efficiency and safety of quantum communication in a noisy environment.     

Multi-party covert communication with steganography and quantum secret sharing

In this paper, we address the “multi-party covert communication”, a stronger notion of security than standard secure multi-party communication. Multi-party covert communication guarantees that the process of it cannot be observed. We propose a scheme for steganographic communication based on a channel hidden within quantum secret sharing (QSS). According to our knowledge nobody has ever raised the scheme, providing us the motivation for this work. To an outside observer, participants will engage in a typical instance of QSS, just like the others. But when the session is over, covert multi-party communication has already been done. Further analysis shows that the amount of hidden information one can acquire is 0, even if either an outside observer guesses the covert communication is carrying on or a dishonest participant is eavesdropping.     

Restoration of three-qubit entanglements and protection of tripartite quantum state sharing over noisy channels via environment-assisted measurement and reversal weak measurement

The restoration of three-qubit entanglement is investigated under the amplitude damping (AD) decoherence with environment-assisted measurement (EAM) and reversal weak measurement (RWM). The results show that there exists a critical strength of RWM dependent of the initial three-qubit entangled state under a given damping rate of the AD channel, i.e., if the selected RWM strength is higher than the critical strength, the entanglement will be reduced compared to one without RWM. Some three-qubit entangled states cannot be restored. We calculated the restorable condition of the initial entanglement and illustrated the valid area for three-qubit GHZ state and W state. Fortunately, an optimal strength of RWM corresponding to a certain damping rate of AD channels can be found within the valid area for a restorable initial state, by which a noise-infected entanglement can be restored to its maximum value. Particularly, when three qubits of W state are subjected to their respective AD channels, due to the symmetry of three qubits, the W state cannot be decohered provided the EAM is successful, and no RWM is required. This is beneficial to quantum communication over the noisy channel. Applying this protection regime to tripartite QSS and taking appropriate initial entangled state as the quantum channel, the fidelity of the shared state can be improved to the maximum 1 probabilistically. Thus, the decoherence effect of the noisy channels can be significantly suppressed or even avoided.     

A secure rational quantum state sharing protocol

A novel rational protocol to share two arbitrary qubits among multiple parties is investigated in this paper. First, the protocol is presented, which is learned from Li et al.’s protocol. Second, the utility, security, correctness, fairness, Nash equilibrium, and Pareto optimality of our scheme are discussed in detail, where the utility, correctness, and fairness of rational quantum state sharing protocols are creatively given because the agent who recovers the state plays a different and more important role. Another important point is that assumptions about our protocol are more practical and suitable than existing protocols.     

基于Cluster态的n位量子态共享方案

为达到n位量子态秘密共享的目的,建立四粒子Cluster态和五粒子Cluster态的量子信道,提出两个量子秘密共享方案。Cluster态与其它纠缠态(W态和GHZ态)不同,相比最大纠缠态,其在某些方面具有很好的稳定性,且实验容易制备。两个方案均只用两次bell测量。第一个方案中,重构者只需对所持有的粒子进行相应的幺正变换即可;第二个方案引入一个辅助粒子最后实施CNOT操作就可恢复原始秘密。对于任意量子态的共享方案,都可以根据需要将最终量子态通过相应的量子线路得到所需要恢复的初始量子态。在安全性方面,分析外部攻击和内部攻击,得到所提出的方案是安全的。     

A centralized quantum switch network based on probabilistic channels

We present a practical scheme for deterministically teleporting quantum information via probabilistic communication channels in a centralized quantum switch network. In the network, a central quantum switch agent is assigned for regulating probabilistic channels so as to construct a direct deterministic channel between the sender and the receiver. This scheme is further extended to a hierarchical network and a tree network involving multiple agents. The advantage of the scheme is that all required multi qubit gates from distributed terminal agents are uniformly performed by a central agent, with which the physical design of terminal nodes is greatly simplified and more reliable deterministic teleportation can be realized in a centralized quantum probabilistic network.     

Asymmetric multi-party quantum state sharing of an arbitrary m-qubit state

We present a scheme for asymmetric multi-party quantum state sharing of an arbitrary m-qubit state with n agents. The sender Alice first shares m − 1 Bell states and one n + 1-particle Greenberger–Horne–Zeilinger state with n agents, where the agent Bob, who is designated to recover the original m-qubit state, just keeps m particles and other agents (all controllers) n − 1 particles, that is, each controller only holds one particle in hand. Subsequently, Alice performs m Bell-basis measurements on her 2m particles and each controller only need take a single-particle measurement on his particle with the basis X. Finally, Bob can recover the original m-qubit state with the corresponding local unitary operations according to Alice and all controllers’ measurement results. Its intrinsic efficiency for qubits approaches 100%, and the total efficiency really approaches the maximal value, which is higher than those of the known symmetric schemes.     

Threshold quantum state sharing based on entanglement swapping

A threshold quantum state sharing scheme is proposed. The dealer uses the quantum-controlled-not operations to expand the d-dimensional quantum state and then uses the entanglement swapping to distribute the state to a random subset of participants. The participants use the single-particle measurements and unitary operations to recover the initial quantum state. In our scheme, the dealer can share different quantum states among different subsets of participants simultaneously. So the scheme will be very flexible in practice.     

Dynamic quantum secret sharing protocol based on GHZ state

This work proposes a new dynamic quantum secret sharing (DQSS) protocol using the measurement property of Greenberger–Horne–Zeilinger state and the controlled-NOT gate. In the proposed DQSS protocol, an agent can obtain a shadow of the secret key by simply performing a measurement on single photons. In comparison with the existing DQSS protocols, it provides better qubit efficiency and has an easy way to add a new agent. The proposed protocol is also free from the eavesdropping attack, the collusion attack, and can have an honesty check on a revoked agent.     

三态纠缠的可控的量子秘密共享协议

提出由3个节点组成的星型量子网络中,基于三态纠缠的可控的量子秘密共享协议。在协议中,3个节点S₁、S₂、S₃共享2N个GHZ-like states,发送编码序列,利用可控制的状态参量α,将测量结果的联合计算共享密钥。理论分析证明,该协议对于外在的窃听者Eve和内在的窃听者都具有很高的安全性。如果存在窃听者,则必然发现,从而保证了共享量子密钥的安全性。     

Controlling the loss of quantum correlations via quantum memory channels

Quantum Information Processing - We consider the support of the limit distribution of the Grover walk on crystal lattices with the linear scaling. The orbit of the Grover walk is denoted by the...     

Distinguishing quantum channels via magic squares game

We study the effect of quantum memory in magic squares game when played in quantum domain. We consider different noisy quantum channels and analyze their influence on the magic squares quantum pseudo-telepathy game. We show that the probability of success can be used to distinguish the quantum channels. It is seen that the mean success probability decreases with increase of quantum noise. Where as the mean success probability increases with increase of quantum memory. It is also seen that the behaviour of amplitude damping and phase damping channels is similar. On the other hand, the behaviour of depolarizing channel is similar to the flipping channels. Therefore, the probability of success of the game can be used to distinguish the quantum channels.     

Multi-party semi-quantum key distribution-convertible multi-party semi-quantum secret sharing

This paper proposes a multi-party semi-quantum secret sharing (MSQSS) protocol which allows a quantum party (manager) to share a secret among several classical parties (agents) based on GHZ-like states. By utilizing the special properties of GHZ-like states, the proposed scheme can easily detect outside eavesdropping attacks and has the highest qubit efficiency among the existing MSQSS protocols. Then, we illustrate an efficient way to convert the proposed MSQSS protocol into a multi-party semi-quantum key distribution (MSQKD) protocol. The proposed approach is even useful to convert all the existing measure–resend type of semi-quantum secret sharing protocols into semi-quantum key distribution protocols.     

利用纠缠态实现任意N粒子量子态的秘密共享

针对量子秘密共享的量子态局限于最大纠缠态的问题,提出一种实现任意N位量子态的秘密共享方案。该方案使用纠缠态作为量子信道,首先发送方对粒子进行Bell基测量,然后接收方Bob或Charlie使用单粒子测量,最后参与者根据Alice和单粒子测量得到的结果,选用合适的联合幺正变换对量子态进行相应的变换,这样可以实现任意N粒子量子态的秘密共享。该方案能够抵御外部窃听者和内部不诚实参与者的攻击,安全性分析表明此方案是安全的。     

The general theory of three-party quantum secret sharing protocols over phase-damping channels

The general theory of three-party QSS protocols with the noisy quantum channels is discussed. When the particles are transmitted through the noisy quantum channels, the initial pure three-qubit tripartite entangled states would be changed into mixed states. We analyze the security of QSS protocols with the different kinds of three-qubit tripartite entangled states under phase-damping channels and figure out, for different kinds of initial states, the successful probabilities that Alice’s secret can be recovered by legal agents are different. Comparing with one recent QSS protocol based on GHZ states, our scheme is secure, and has a little smaller key rate than that of the recent protocol.     

Shared quantum control via sharing operation on remote single qutrit

Two qubit-operation-sharing schemes (Zhang and Cheung in J. Phys. B 44:165508, 2011) are generalized to the qutrit ones. Operations to be shared are classified into three different classes in terms of different probabilities (i.e, 1/3, 2/3 and 1). For the latter two classes, ten and three restricted sets of operations are found out, respectively. Moreover, the two generalized schemes are amply compared from four aspects, namely, quantum and classical resource consumption, necessary-operation complexity, success probability and efficiency. It is found that the second scheme is overall more optimal than the first one as far as three restricted sets of operations are concerned. Moreover, the experimental feasibility of our schemes is confirmed with respect to the nowaday technique.     

Perfect state transfer via quantum probability theory

The transfer of quantum states plays an important role in quantum information processing. In fact, the transfer of a quantum state from point A to point B with unit fidelity has been the center of attention during the last decades. One of the ways to aim this goal is to transfer a quantum state in a spin chain described by designing a Hamiltonian in which a mirror symmetry with respect to the network center is created. In this paper, we introduce a method based on the spectral distribution of the adjacency matrix and stratifying a spin network, with respect to an arbitrary vertex denoted by o which is called starting vertex (reference vertex), to make perfect quantum state transfer possible between antipodes in the spin network. Then we design the coupling coefficients in a way to create a mirror symmetry in the Hamiltonian with respect to the center of the network. In this method the initial state is encoded on the starting vertex and then it is received at its antipode. There is no need to consider any external control in this approach.