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In this article, we present a quantum model of the two-qutrit (T-Q) in the Λ-type configuration interacting with a field mode initially in a coherent state of power lower potential. We analyze the dynamical characteristics of this quantum system, taking into account the influences of both the T-Q initial state and the field parameters. We investigate the entanglement between the T-Q and field, the Q–Q state entanglement, as well as the T-Q quantum coherence. We quantify the nonclassical properties of the power lower potential field based on the evolution of the Mandel parameter. The effects of power lower potential parameters on the evolution of quantum measures such as negativity, quantum coherence, von Neumann entropy, and the Mandel parameter are analyzed when the T-Q are initially in the upper and Bell states. Our findings indicate that the system exhibits a quasi-periodic occurrence of maximum entanglement and coherence when the T-Q are initially in the Bell state.

Teleportation across short distances has become relevant in view of some recent developments in quantum technology. The advantage here is that certain auxiliary qubits can be accessed and utilized by both the sender and the receiver. Such an act reduces the requirement of the number of qubits in the entangled quantum channel which would have been otherwise necessary. In this paper we present a short-distance teleportation protocol by which an unknown three-qubit state can be transferred with the help of auxiliary qubits and a maximally entangled Bell State. In the second part of the paper we introduce a probabilistic short-distance protocol for the same unknown three-qubit state by using a non-maximally entangled Bell-state. The success probability of the protocol is calculated and its relation with the first protocol is discussed. We presented a circuit diagram for the first protocol and executed it in the IBM-Quantum platform. [ABSTRACT FROM AUTHOR]

Quantum private comparison (QPC) represents a cryptographic approach that enables two parties to determine whether their confidential data are equivalent, without disclosing the actual values. Most existing QPC protocols utilizing single photons or Bell states are considered highly feasible, but they suffer from inefficiency. To address this issue, we present a novel QPC protocol that capitalizes on the entanglement property of Bell states and local operations to meet the requirements of efficiency. In the proposed protocol, two participants with private inputs perform local operations on shared Bell states received from a semi-honest third party (STP). Afterward, the modified qubits are returned to the STP, who can then determine the equality of the private inputs and relay the results to the participants. A simulation on the IBM Quantum Cloud Platform confirmed the feasibility of our protocol, and a security analysis further demonstrated that the STP and both participants were unable to learn anything about the individual private inputs. In comparison to other QPC protocols, our proposed solution offers superior performance in terms of efficiency. [ABSTRACT FROM AUTHOR]

This research presents a new bidirectional quantum teleportation (BQT) protocol for transmitting two single-qubit states from Alice to Bob and a three-qubit entangled state from Bob to Alice, simultaneously. The protocol utilizes shared entanglement between the parties and requires performing two Bell-state measurements and a GHZ-state measurement. The protocol’s functionality is validated by implementing the circuit in the Qiskit library. Moreover, the effects of amplitude–damping noise and bit-flip noise are evaluated and analyzed. The protocol is compared with the recent schemes and its effectiveness is shown in terms of efficiency of the transmitted information. The protocol will contribute to the advancement of bidirectional quantum teleportation protocols. [ABSTRACT FROM AUTHOR]

Quantum secret sharing as a privacy‐preserving scheme necessitating collaborative efforts from all participating users to collectively recover encrypted information. This paper introduces a novel dynamic multi‐party to multi‐party quantum secret sharing protocol based on Bell states, enabling secure sharing of secrets among dynamically changing multi‐party. The protocol innovatively employs Bell states combined with simplified local unitary operations, significantly reducing the complexity and enhancing the scalability of practical implementations in quantum communication systems. Particularly, through simulation using IBM's Qiskit framework, its correctness and practicality are confirmed. Security analysis demonstrates that the protocol effectively withstands common attack methods, providing reliability, and security in quantum communication. This research presents a more flexible and efficient solution in the field of quantum secret sharing. [ABSTRACT FROM AUTHOR]

Quantum secure direct communication is a significant branch of quantum cryptography. Recently, a quantum secure direct communication scheme based on intermediate-basis was proposed (Liang et al. in Front Phys 18(5):51301, 2023 https://doi.org/10.1007/s11467-023-1284-4). It is believed that the scheme can improve the efficiencies of security detection and information encoding by utilizing the intermediate-basis. However, this paper points out two serious problems with the aforementioned scheme. Firstly, it fails to utilize two distinct bases since the intermediate-basis is merely a variant of the Bell basis. Accordingly, the quantum secure direct communication scheme based on intermediate-basis cannot achieve the promised high efficiency. Secondly, even if the intermediate-basis is substituted with another quantum basis, the modified quantum secure direct communication scheme cannot achieve the promised high efficiency because the receiver cannot correctly decode the secret message from the final entangled pairs. It is crucial to design correct and efficient quantum secure direct communication protocols. This work can remind the developers of quantum secure direct communication to avoid such pitfalls when they enhance the robustness and efficacy of their schemes. [ABSTRACT FROM AUTHOR]

In this paper, a channel-optimized quantum communication scheme with imperfect Bell states is being considered, based on quantum teleportation and error correction codes technology. In this scheme, a novel "combination code" technique is proposed to protect the pre-shared Bell states from storage errors and to safeguard the information-encoded states from noisy channels. Ultimately, it is revealed by Monte Carlo simulation results that the channel fidelity of the proposed channel-optimized quantum communication scheme with imperfect Bell states is significantly advantageous over standard quantum error-correcting code (QECC) and entanglement-assisted quantum error-correcting code (EAQECC) communication schemes. [ABSTRACT FROM AUTHOR]

In this paper, we present a quantum multi-signature scheme based on Bell state. It allows n ( n > 1 ) signers sign a same file in random order. Bell states are used as information carriers and transmitted among verifier, requester, and signers. In this way, the verifier can verify the correctness of the signature. It is shown that our scheme satisfies the unforgeability and nondeniability of a secure quantum signature in theory and can resist collusive attack. In addition, only the Hadamard operator and four Pauli operators are used to generate a signature, which makes our scheme more feasible. [ABSTRACT FROM AUTHOR]

Information-theoretically secure authentication is necessary to guarantee both the authenticity and integrity of the data transferred over the channel in quantum key agreement (QKA). Generally speaking, QKA uses quantum resources to negotiate a unique shared key for every communication; consequently, as the number of communications rises, so does the quantity of quantum key resources used. A secure mutual authentication QKA scheme for the two-party setting with key recycling is proposed, based on single-photon states and Bell states, to realize mutual authentication and minimize quantum key consumption. The proposed protocol generates symmetric keys and authenticates each other using quantum states. Multiple rounds of communication can be accomplished with different keys when combined with key recycling. Additionally, security analysis and efficiency comparison show that our scheme can achieve desirable results with existing quantum technologies. [ABSTRACT FROM AUTHOR]

Quantum private query (QPQ) can protect both user and database privacy when a user retrieves an entry from a database. Most existing QPQ protocols only support a single user retrieving a database, but in reality, people collaborate with each other to complete a task. Thus, it is necessary for multiple users to simultaneously retrieve a database. So far, all proposed multi-user QPQ protocols are based on high-dimensional quantum states and do not consider external attackers. In this paper, we present a multi-user QPQ protocol with two-way authentication based on Bell state and entanglement swapping technology. Under the premise of ensuring the privacy of users and the database, this protocol enables multiple users to simultaneously retrieve entries from a database. The security analysis demonstrates that the protocol can ensure privacy and resist external attacks. [ABSTRACT FROM AUTHOR]

In this paper, we consider to solve the problem of reducing the end-to-end quantum entanglement establishment latency in quantum networks. In some existing schemes, "doubling" entanglement swapping (ES) method is usually utilized in a nested quantum repeater structure, while we investigate parallel-measurement techniques. We propose a protocol for end-to-end entanglement establishment in a quantum network where heterogeneous Bell pairs are previously shared on physical links. The protocol is proven to be feasible theoretically in a generalized scenario with multiple quantum repeater nodes. A general decision mechanism is developed for the destination node to read out the state of end-to-end quantum entanglement locally based on knowledge of the received measurement outcomes and entangled links information. Numerical evaluation shows that our protocol outperforms the "doubling" ES scheme regarding to the end-to-end entanglement establishment latency. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel verifiable quantum secret sharing scheme tailored for a specific class of low-density parity-check (LDPC) codes. In the proposed protocol, Alice, the dealer, initially utilizes the generator matrix of the chosen LDPC code to calculate all secret shares and distributes individual shares to all participants in a quantum secure direct communication channel. In the distribution phase, each participant computes a hash value based on their respective share and a randomly generated sequence, which is then published. In the recover phase, each participant performs a unitary operation on these received particles and sends them to the next participant using the decoy-photon technique. Furthermore, the last participant performs Bell measurements on the final quantum states to obtain the original secret. At last, we demonstrate our protocol to be secure against intercept-and-resend attack, entangle-and-measure attack and dishonest participant attack. In addition, we present a comparison of our protocol with other existing schemes. [ABSTRACT FROM AUTHOR]

Quantum private comparison (QPC) represents a cryptographic approach that enables two parties to determine whether their confidential data are equivalent, without disclosing the actual values. Most existing QPC protocols utilizing single photons or Bell states are considered highly feasible, but they suffer from inefficiency. To address this issue, we present a novel QPC protocol that capitalizes on the entanglement property of Bell states and local operations to meet the requirements of efficiency. In the proposed protocol, two participants with private inputs perform local operations on shared Bell states received from a semi-honest third party (STP). Afterward, the modified qubits are returned to the STP, who can then determine the equality of the private inputs and relay the results to the participants. A simulation on the IBM Quantum Cloud Platform confirmed the feasibility of our protocol, and a security analysis further demonstrated that the STP and both participants were unable to learn anything about the individual private inputs. In comparison to other QPC protocols, our proposed solution offers superior performance in terms of efficiency.

In many communication scenarios, it is necessary to involve a third party for control and supervision. In the context of controlled bidirectional quantum secure direct communication (CBQSDC) protocols, the transmission of secret messages between two legitimate users is only permitted with the explicit permission of a controller. To address the issue of controlled communication, a CBQSDC protocol (CLYH2015) utilizing Bell states was proposed in the paper (Quant Inf Process 14, 3515–3522, 2015). Bell states have been widely recognized for their significance in the field of quantum secure direct communication. In a subsequent study published in (Quant Inf Process 16, 147, 2017), the research examined whether CLYH2015 protocol strictly requires the initial states to be Bell states. The conclusion drawn from this investigation is that CLYH2015 protocol working properly necessitates the use of Bell states as initial states. To explore alternative possibilities for the initial states in CLYH2015 protocol, a class of CBQSDC protocols employing the generalized Bell states (GBell states), a | 00 ⟩ + b | 11 ⟩ , b ¯ | 00 ⟩ - a ¯ | 11 ⟩ , a | 01 ⟩ + b | 10 ⟩ , and b ¯ | 01 ⟩ - a ¯ | 10 ⟩ , are designed where a and b are complex numbers with | a | = | b | = 1 2 , a ¯ and b ¯ the conjugate complex numbers of a and b, respectively. The class of designed CBQSDC protocols demonstrates several favorable properties, including resistance against information leakage, intercept-and-resend attacks, measure-resend attacks, as well as robustness against collective attacks. In addition, the unconditional security of the class of designed protocols is proved. Finally, to show the advantages of the class of designed protocols, they are compared with some with some previous closely associated protocols. Interestingly, it is worth noting that the Bell states can be considered a special case of the GBell states when both a and b are real numbers. Consequently, CLYH2015 protocol can be regarded as a particular instance of the designed CBQSDC protocols. This insight implies that the initial states in CLYH2015 protocol can be extended to include the GBell states, rather than being limited solely to the Bell states. [ABSTRACT FROM AUTHOR]

We give a necessary condition for photon state transformations in linear optical setups preserving the total number of photons. From an analysis of the algebra describing the quantum evolution, we find a conserved quantity that appears in all allowed optical transformations. We give some examples and numerical applications, with example code, and give three general no-go results. These include (i) the impossibility of deterministic transformations which redistribute the photons from one to two different modes, (ii) a proof that it is impossible to generate a perfect Bell state with an arbitrary ancilla from the Fock basis and (iii) a restriction for the conversion between different types of entanglement (converting GHZ to W states). These tools and results can help in the design of experiments for optical quantum state generation.

Multi-party quantum private comparison (MQPC) assumes responsibility for overseeing the flow of data and communication among diverse entities, wherein it boasts powerful security capabilities that have garnered substantial attention. Most current MQPC protocols rely on difficult-to-prepare quantum states and are inefficient in their use of resources. In this paper, we propose a novel MQPC protocol without entanglement swapping, thereby building upon the assumption of an ideal channel. This protocol is based on Bell states, which simplifies implementation and addresses the challenges associated with using complex quantum states; it also enables the comparison of secret information by having a trusted party prepare and transmit encoded quantum sequences to participants, thereby facilitating efficient equality comparison among all parties. Our MQPC protocol showcased remarkable efficiency in comparison to existing protocols for quantum private comparison. Furthermore, the incorporation of decoy photon and shared key technologies made external and internal attacks ineffective, thereby ensuring the utmost security and integrity of the protocol. [ABSTRACT FROM AUTHOR]

Bell state measurement is vital to quantum information technology. Conventional linear optical elements, however, cannot fully distinguish all polarization Bell states without assisting of additional degrees of freedom. Leveraging on a pair of binary-pixel metasurfaces, we demonstrate direct measurement of all four polarization Bell states. Each metasurface is designed to produce two output modes that linearly superpose three Bell states in the coincidence counting measurement. By rotating the polarizers, the coincidence counting measurement achieves a tunable anticorrelation between one and the other two Bell states, achieving Bell state detection efficiency of 75% in a single measurement. Complete and deterministic Bell state measurement is further realized by performing two measurements. Our work shows the advantage of utilization of metasurfaces in quantum detection schemes and is of great applicative interest for quantum dense coding, entanglement swapping, quantum teleportation protocols, and novel quantum information processing tasks.

In this article, we first propose a deterministic bidirectional quantum teleportation scheme in the framework of general multi-hop network. In the scheme, three-qubit GHZ state and Bell state play the role of shared resources. The shared quantum channel is determined by the parity of the hop number of the communication network. Entanglement swapping of distant participants is accomplished by Bell state measurement and two-qubit measurement. Receivers at each side can recover the target state according to general formulas with one hundred percent. Then, we give the general form of our scheme in noisy environment. The performance of the scheme in four-hop network suffering bit flip noise is presented as an illustrative example. [ABSTRACT FROM AUTHOR]

In cryptography, oblivious transfer (OT) is an important multiparty cryptographic primitive and protocol, that is suitable for many upperlayer applications, such as secure computation, remote coin-flipping, electrical contract signing and exchanging secrets simultaneously. However, some nogo theorems have been established, indicating that one-out-of-two quantum oblivious transfer (QOT) protocols with unconditional security are impossible. Fortunately, some one-out-of-two QOT protocols using the concept of Crépeau's reduction have been demonstrated not to conform to Lo's no-go theorem, but these protocols require more quantum resources to generate classical keys using all-or-nothing QOT to construct one-out-of-two QOT. This paper proposes a novel and efficient one-out-of-two QOT which uses quantum resources directly instead of wasting unnecessary resources to generate classical keys. The proposed protocol is not covered by Lo's no-go theorem, and it is able to check the sender's loyalty and avoid the attack from the receiver. Moreover, the entangled state of the proposed protocol is reusable, so it can provide more services for the participants when necessary. Compared with otherQOT protocols, the proposed protocol is more secure, efficient, and flexible, which not only can prevent external and internal attacks, but also reduce the required resources and resource distribution time. [ABSTRACT FROM AUTHOR]

Controlled quantum teleportation schemes require the existence of a third party acting as a teleportation controller, so that without its cooperation, quantum information of the unknown state cannot be transmitted. Here, we propose a new controlled quantum teleportation scheme to perfectly transmit an arbitrary entangled three-qubit state. In this scheme, quantum information of unknown three-qubit arbitrary state is transmitted from Alice, the sender to Bob, the remote receiver via a quantum channel consisting of two GHZ entangled states and a Bell entangled state under the supervision of Charlie, the controller. Bob can then recover the desired three-qubit arbitrary state by performing appropriate unitary Pauli transformations, and we find that our protocol works perfectly. This scheme could be quite easily extended to accurately teleport an unknown N-qubit state from Alice to Bob under Charlie's control, using (N − 1) GHZ entangled states and a Bell entangled state. [ABSTRACT FROM AUTHOR]

Bell state measurement is vital to quantum information technology. Conventional linear optical elements, however, cannot fully distinguish all polarization Bell states without assisting of additional degrees of freedom. Leveraging on a pair of binary-pixel metasurfaces, we demonstrate direct measurement of all four polarization Bell states. Each metasurface is designed to produce two output modes that linearly superpose three Bell states in the coincidence counting measurement. By rotating the polarizers, the coincidence counting measurement achieves a tunable anticorrelation between one and the other two Bell states, achieving Bell state detection efficiency of 75% in a single measurement. Complete and deterministic Bell state measurement is further realized by performing two measurements. Our work shows the advantage of utilization of metasurfaces in quantum detection schemes and is of great applicative interest for quantum dense coding, entanglement swapping, quantum teleportation protocols, and novel quantum information processing tasks. [ABSTRACT FROM AUTHOR]

In this paper, a novel semiquantum private comparison (SQPC) protocol based on single kind of Bell states is proposed, which allows two classical parties to judge the equality of their private inputs securely and correctly under the help of a semi-honest third party (TP) who possesses complete quantum capabilities. TP is allowed to misbehave on her own but cannot conspire with anyone else. Our protocol needs none of unitary operations, quantum entanglement swapping or the reordering operations. Moreover, our protocol only needs to prepare single kind of Bell states as initial quantum resource. Detailed security analysis turns out that our protocol is secure against various outside and participant attacks. Compared with most of the existing SQPC protocols based on Bell states, our protocol is more feasible in practice. [ABSTRACT FROM AUTHOR]

With the help of semi-honest third party , a new quantum privacy comparison (QPC) protocol is proposed, which can compare the equality of the secrets of three participants without disclosing the secret value. At present, QPC protocols using different quantum states have been proposed. If complex quantum states are used in QPC protocol, more expensive equipment or more complex methods will be required to generate these quantum states, which may reduce efficiency and increase cost. In order to improve the availability of the protocol, a QPC protocol based on classical-quantum authentication channel is proposed in this paper. The protocol takes Bell state as quantum resource and uses single-particle measurement technology to measure particles, so the protocol enables participants to compare quantum privacy without expensive quantum devices. Finally, in order to ensure the security of the protocol, we use decoy photon technology and quantum key distribution technology to encrypt, so that the protocol can resist external attacks and participant attacks. [ABSTRACT FROM AUTHOR]

Multi-party quantum private comparison (MQPC) assumes responsibility for overseeing the flow of data and communication among diverse entities, wherein it boasts powerful security capabilities that have garnered substantial attention. Most current MQPC protocols rely on difficult-to-prepare quantum states and are inefficient in their use of resources. In this paper, we propose a novel MQPC protocol without entanglement swapping, thereby building upon the assumption of an ideal channel. This protocol is based on Bell states, which simplifies implementation and addresses the challenges associated with using complex quantum states; it also enables the comparison of secret information by having a trusted party prepare and transmit encoded quantum sequences to participants, thereby facilitating efficient equality comparison among all parties. Our MQPC protocol showcased remarkable efficiency in comparison to existing protocols for quantum private comparison. Furthermore, the incorporation of decoy photon and shared key technologies made external and internal attacks ineffective, thereby ensuring the utmost security and integrity of the protocol.

In this paper, we introduce a protocol for mutual sharing of known quantum information between different parties. We show that it is possible to exchange known non-maximally entangled Bell states between three parties through a protocol by use of a multipartite entangled state. The scheme is overseen by a controller. [ABSTRACT FROM AUTHOR]

Semi-quantum private comparison(SQPC) is the quantum method to compare the secrets’ equality for two distrustful classical participants without knowing the their accurate information. The four-particle cluster state is more robust against decoherence than any other four-particle state. In this paper, the novel entanglement swapping construction by the four-particle cluster state and Bell state can perform this SQPC protocol well. With the pre-shared secret key sequence, the two distrustful users can obtain promising results without leaking any information to the semi-honest third party (TP). Then, the security analyses indicate that this SQPC protocol is secure against the outside and participant attacks, and more efficient than the similar literature. [ABSTRACT FROM AUTHOR]

In this work we introduce a three-party quantum conference where the involved parties initially hold asymmetric quantum information which are finally shared amongst themselves by the execution of a quantum communication protocol. The three conferencing parties along with a controller are connected amongst themselves through a multipartite quantum entanglement which is used as quantum resource in the protocol. The role of the controller is confined to a final action without which the conference can not be performed. The present work is an instance of applications of multipartite entangled resources in communication problems. [ABSTRACT FROM AUTHOR]

In quantum state discrimination, the observers are given a quantum system and aim to verify its state from the two or more possible target states. In the local quantum state marking as an extension of quantum state discrimination, there are N composite quantum systems and N possible orthogonal target quantum states. Distant Alice and Bob are asked to correctly mark the states of the given quantum systems via local operations and classical communication. Here we investigate the local state marking with N $4\otimes4$ systems, N = 4, 5, 6, and 7. Therein, Alice and Bob allow for three local operations: measuring the local observable either σ _z or σ _x simultaneously, and entanglement swapping. It shows that, given arbitrary four $4\otimes4$ systems, Alice and Bob can perform the perfect local quantum state marking. In the N = 5, 6 cases, they can perform perfect local state marking with specific target states. We conjecture the impossibility of the local quantum state marking given any seven target states since Alice and Bob cannot fulfill the task in the simplest case.

In this paper, we propose a rapid and high-fidelity protocol to generate Bell states by dissipation dynamics and Lyapunov control. With a designed dissipative path, an arbitrary initial state can evolve into the target Bell state with high fidelity. Besides, the evolution is accelerated by Lyapunov control pulses, particularly at the early stage of the evolution. The time consumption of achieving a certain threshold of required fidelity is shortened remarkably. By analyzing the impact of the pulses on the protocol, we show how to select the suitable pulses and their strengths to achieve a better fidelity. At last, we numerically prove that the protocol is robust against possible noises. The results presented in the paper may open a new path to achieve fast and high-fidelity generation of entangled states based on dissipation dynamics. [ABSTRACT FROM AUTHOR]

The four-qubit cluster state has a more robust entanglement property than other four-particle states. Empowered by the 4-qubit cluster state and Bell state entanglement, two quantum secret sharing (QSS) protocols are proposed in this paper. The first protocol is with the quantum users who can perform Bell measurement. The second protocol is with classical users who only can perform Z basis measurement and is also known as semi-quantum secret sharing (SQSS). Moreover, the security analysis shows the proposed QSS and SQSS protocols can achieve full security and resist some common eavesdropping attacks, such as interception attack, measure-resend attack, entanglement-measure attack, and Trojan horse attack. Meanwhile, the efficiency comparison shows that the proposed protocols are also efficient than other similar protocols with relate to the qubit efficiency. [ABSTRACT FROM AUTHOR]

Quantum computers are very efficient in terms of speed and security. Decoherence and architectural complexity restrict the control of sensitive quantum information as the number of qubits in a quantum computer increases. Therefore, it is more convenient to make a device with multiple quantum processors with small number of qubits instead of making a device with a large number of qubits quantum processors. The implementation of controlled unitary gates is a problem in such nonlocal systems. The methods in the literature for this problem use entangled qubit pairs, classical communication channels and classical bits. The existing methods perform some unitary operations on the target state for reconstruction after sending information through classical communication channels and applying quantum measurements on control states. In this study, a generalized method for nonlocal implementation of multi-qubit controlled unitary quantum gates with quantum channel is proposed. The proposed method can implement any controlled gate on the control and target qubits that are far from each other in terms of location. The method does not require classical channels and classical bits, any extra unitary operation for reconstruction. The proposed method is both more secure and uses less resources for operations than the other hybrid methods in the literature. Comparisons with existing studies are given in terms of required entangled qubit pairs, classical channels and bits, extra unitary operations for reconstruction the target state, and the advantages of the proposed method are revealed. [ABSTRACT FROM AUTHOR]

We present an economical entanglement purification protocol for the multi-photon polarization-entangled system in a Greenberger–Horne–Zeilinger (GHZ) state. We use one pair of two-photon Bell state or M-photon GHZ state ( M < N ) to correct the error in the polarization entanglement of an N-photon system. This protocol only uses linear optical elements, so that it is feasible in current experiment. The parties can obtain a high-quality entangled polarization state from each less-entangled N-photon system, by consuming only the Bell state, or the M-photon GHZ state. It is far different from conventional multipartite entanglement purification protocols. It also requires less local operation and classical communication than other purification protocols. Our protocol especially suits for the case where we can precisely know which channel or channels are more noisy. This protocol may be useful in current and future long-distance quantum communication. [ABSTRACT FROM AUTHOR]

We propose a bidirectional controlled teleportation scheme using two pairs of Bell states as quantum channels. This solution uses Charlie as the controlled party. After two Bell state measurements, while Alice sends any single particle state to Bob, Bob can also send any single particle state to Alice, thus successfully completing the bidirectional controlled teleportation. Our plan is also compared with several other protocols from five aspects to illustrate that the plan has certain advantages. This makes our scheme relatively simpler and easier to implement and more maneuverable. [ABSTRACT FROM AUTHOR]

Security, efficiency and universality are the major concerns in distributed computation for how to communicate securely as there are a large number of nodes that require interactive authentication. These become more challenging especially for the multi-party quantum environment as it is highly complicated and heterogeneous in nature. Hence, based on bell states and unitary operation, we propose a multi-party quantum group key distribution protocol. The initial two participants are generated by election algorithm to ensure the fairness among the participants in our protocol. Next, mutual authentication is provided by two Bell states of four orthogonal maximal states, and the group session key is obtained by combining unitary operation. The main innovations of this scheme are that the authenticated information with the group key is transmitted among the ordered participants, and the efficiency of our protocol is acceptable which the time complexity of QKD is O log 2 N with the N-party. Through security analysis and efficiency analysis, the protocol can effectively resist internal attacks and external attacks, and has feasible efficiency. [ABSTRACT FROM AUTHOR]

We propose a scheme for teleportation of an arbitrary two-qubit state by using a Bell state as the quantum channel working together with an auxiliary qubit. Our scheme needs less entanglement resource, but at the cost of shortening teleportation distance. This is because that in order to successfully recover the teleported state, both sender and receiver need to implement quantum-gate operations on the shared auxiliary qubit. So, the auxiliary qubit must be close to both sender and receiver. Otherwise, the sender and receiver cannot carry out quantum-gate operations on it. Thus, our scheme is invalid for long-distance teleportation. But for short-distance teleportation, our scheme is an optimal choice because it requires less entanglement resource. From a practical point of view, our scheme is very promising for application in quantum teleportation on chip. [ABSTRACT FROM AUTHOR]

Multi-hop teleportation is a quantum teleportation scheme for transferring quantum states on a large scale. In this paper, a new multi-hop teleportation protocol is investigated for transferring arbitrary N-qubit states between M-neighbor nodes. In this scheme, intermediate nodes are connected with each other by symmetric entangled Bell states as quantum channels. First, one-hop teleportation of single-qubit, two-qubit and N-qubit states are introduced, then this method is generalized to two-hop and multi-hop teleportation for N-qubit. Also, we calculate the efficiency of this scheme. [ABSTRACT FROM AUTHOR]

We remark that the quantum key agreement protocol (Yang et al. in Quantum Inf Process 18(10):322, 2019) is flawed. It is unnecessary for Bob to prepare his secret key K B , because it is finally announced and accessible to adversaries. We find, K B has no relation to the confidentiality of the final agreed key K AB = K A ⊕ K B . It is just a key transfer scheme, not a general key agreement scheme. We also find there is short of a code for Bob to extract bits from the measured results. [ABSTRACT FROM AUTHOR]

A four-party single-qubit operation sharing scheme is put forward by utilizing the Bell and Yeo–Chua product state in an entanglement structure as the composite quantum channel. Four features of the scheme are discussed and confirmed, including its determinacy, symmetry, and security as well as the scheme experimental feasibility. Moreover, some concrete comparisons between our present scheme and a previous scheme [H. Xing et al., Quantum Inf. Process. 13 (2014) 1553] are made from the aspects of quantum and classical resource consumption, necessary operation complexity, and intrinsic efficiency. It is found that our present scheme is more superior than that one. In addition, the essential reason why the employed state in the entanglement structure is applicable for sharing an arbitrary single-qubit operation among four parties is revealed via deep analyses. With respect to the essential reason, the capacity of the product state in quantum operation sharing (QOS) is consequently shown by simple presenting the corresponding schemes with the state in other entanglement structures. [ABSTRACT FROM AUTHOR]

Recently, Chen et al. [Int. J. Theor. Phys. 59, 1402–1412 (2020)] proposed a theoretical scheme for controlled quantum teleportation (CQT) of a Bell state by using seven-qubit entangled state as a quantum channel. In this comment, it is shown that the consumption of both the quantum and classical resources used by Chen et al. is excessively high because the actual task of CQT of a Bell state via seven-qubit entangled state can be reduced to the CQT of an arbitrary single-qubit state via three-qubit GHZ state. Hence, in this work, an improved scheme for CQT has been presented. We have also shown that the CQT of certain class of N-qubit entangled state can also be realized successfully by using a three-qubit GHZ state as the quantum channel. The intrinsic efficiency of the present communication scheme is very large as compared to that proposed by Chen et al. [ABSTRACT FROM AUTHOR]

Luo and Hwang [Quantum Inf. Process (2016) 15:947–958] proposed the authenticated semi-quantum direct communication protocols for a quantum participant to be able to transmit secret messages to a classical participant without employing an authenticated classical channel. However, this study indicates that there is an information leakage problem in Luo and Hwang's measure-resend protocol. The information leakage problem might allow an attacker to use an intercept-resend attack to obtain partial secret messages. Finally, an improved method is proposed to overcome the information leakage problem. [ABSTRACT FROM AUTHOR]

Quantum state sharing (QSTS) is a hot topic in quantum cryptography. However, majority of the current structures cannot resist the participant's fraud well during the initial state reconstruction phase. Especially, verifiable QSTS scheme which can be used to share unknown quantum state has yet to emerge. In this paper, we will propose the first verifiable structure by improving an existing threshold QSTS scheme. Our scheme has three merits: 1) it is easily realized in physical experiment because only the simple oneparticle unitary operations were involved; 2) each dishonest behavior of one participant could be detected by the next client; and 3) the private key of the dealer could be reused for many times.