Narrow Results

A three-party controlled deterministic secure quantum communication scheme through entanglement swapping is proposed firstly. In the scheme, the sender needs to prepare a class of Greenberger–Horne–Zeilinger (GHZ) states which are used as quantum channel. The two communicators may securely communicate under the control of the controller if the quantum channel is safe. The roles of the sender, the receiver, and the controller can be exchanged owing to the symmetry of the quantum channel. Different from other controlled quantum secure communication schemes, the scheme needs lesser additional classical information for transferring secret information. Finally, it is generalized to a multiparty controlled deterministic secure quantum communication scheme.

A scheme is proposed for remotely preparing a class of three-particle GHZ states by using a Bell state and a three-qubit GHZ state as the quantum channel. In the scheme, a two-qubit collective state measurement is performed and the necessary classical communication cost is 0.25 cbit on average. In general, the target state can be successfully prepared with the probability 1/4. However, if the state belongs to some special classes, the preparation success probability can reach 0.5 or even 1 after consuming a little additional classical resource. Comparing with the recent scheme [Opt. Commun.281, 871 (2008)], the present scheme has some advantages, e.g., the simpler quantum joint measurement and the less classical resource consumption.

Recently, Zheng et al. presented a novel signature protocol with arbitrator based on XOR encryption and GHZ state. Unfortunately, their protocol lacks security. Firstly, a quantum adversary can forge their signature based on the received information. On the other hand, their protocol is vulnerable for the adversary’s repudiation attack. Then, we bring about improvements on its security, efficiency and practicality. The improved protocol not only prevents the security defects of the old protocol, but also has better computation efficiency. On the other hand, our protocol is mainly used to sign the classical messages, which are widely used in the current network.

We show how a non-local quantum CNOT with (N-1)-target operation can be implemented with unit fidelity and unit probability by using a N-qubit maximally entangled GHZ state as quantum channel. We also put forward two schemes for probabilistic implementing the operation with unit fidelity by employing a partially entangled pure GHZ state as quantum channel. The overall physical resources required for accomplishing these schemes are different, and the successful implementation probabilities are also different. We also point out the non-local CNOT with (N-1)-target operation can be used as a purification protocol to concentrate entanglement from an ensemble of partially entangled GHZ states into a subensemble of maximally entangled ones.

In this paper, an asymmetric bidirectional controlled quantum teleportation via a six-qubit partially entangled state is given, in which Alice wants to transmit a two-qubit entangled state to Bob and Bob wants to transmit a single-qubit state to Alice on the same time. Although the six-qubit state as quantum channel is partially entangled, the teleportation is implemented deterministically. Furthermore, only Bell-state measurements, single-qubit measurements and some unitary operations are needed in the scheme.

We present a scheme to generate the tripartite GHZ state via cavity quantum electrodynamics. Our scheme is based on the resonant interaction of a V-type three-level atom with the cavity fields for precalculated interaction time. Also, this scheme can be directly generalized to prepare the general n-qubit GHZ state.

By exploiting the fermionic qubit parity measurement, we present a scheme to realize quantum non-demolition (QND) measurement of Bell states and generate n-party GHZ state in quantum dot. Compared with the original protocol, the required electron transfer before and after parity measurement can be nonadiabatic, which may speed up the operation speed and make the omitting of spin-orbit interaction more reasonable. This may help us to construct CNOT gate without highly precise control of coupling as the way of D. Gottesman and I. L. Chuang.

A proactive quantum secret sharing scheme is proposed, in which the participants can update their shadows periodically. In an updating period, one participant randomly generates the GHZ states and sends the particles to the other participants, and the participants update their shadows according to the measurement performed on the particles. After an updating period, each participant can change his shadow but the secret is changeless. The old shadows will be useless even if they have been stolen by the attacker. The proactive property is very useful to resist the mobile attacker.

In this paper, we design a scheme where a polarization Greenberger–Horne–Zeilinger (GHZ) state can be completely and deterministically distinguished by adopting linear momentum degree of freedom as the ancillary qubits or change of roles between the momentum and polarization degrees of freedom. Two ways for distinguishing three-photon GHZ state can be achieved in just one quantum circuit.

Quantum entanglement and nonlocality will suffer inevitable harm from decoherence environment. Based on GHZ state, we study the harm of the generalized amplitude damping (GAD) operation and the protection by the single local filtering (SLF) operation in this paper. We verify that the SLF functions to depress the loss of entanglement and nonlocality from GAD. This conclusion will guide us to select the best method to protect the GHZ state from GAD decoherence.

Dynamic quantum secret sharing occupies an important position in quantum cryptography. In this paper, an efficient and secure dynamic quantum direct two-secrets sharing scheme is proposed based on the GHZ state. The proposed scheme is a one-time sharing of a determined classic message and quantum states. For recovering the secret messages, the agents only need to have the ability to perform X-basis measurements on the particles without performing any unitary operation. When dynamically deleting agents, our scheme only requires the other agents to announce some information without transmitting any quantum. Moreover, the analysis shows that our scheme is able to resist dishonest revoked agent attack as well as a range of other common attacks. Compared with the existing dynamic quantum direct secret sharing schemes, the proposed scheme is more efficient and more secure.

Quantum entanglement, like other resources, is now considered to be a resource. It can be produced, concentrated if required, swapped, transported and consumed. During recent years, various schemes of quantum state teleportation have been proposed using different types of quantum channels. Not restricting to qubit based systems, qutrit states and channels have also been of considerable interest. In the present paper, we investigate the teleportation of an unknown single qutrit state, as well as a two qutrit state through a three qutrit quantum channel, along with the required operations to recover the state. This is further generalized to the case of teleportation of an n-qutrit system.

We present a quantum information splitting scheme of a two-qubit state by using two Greenberger–Horne–Zeilinger (GHZ) states as quantum channels. In this scheme, since the sender Alice knows the quantum information in priori, she only needs to perform a two-qubit measurement and publish two classical bits for her two agents Bob and Charlie to reconstruct the quantum information via their mutual assistance. We calculate the success probability and classical communication cost within the scheme. In the general case, Alice can successfully split the state with probability 25% (probabilistic) and the classical communication cost is 4 classical bits. However, in some special cases, the secret states are chosen from a special ensemble, the success probability of our scheme can be increased to 50% or even to 100% (deterministic) after consuming some extra classical bits.

In this paper, we present a scheme to prepare the W state and the GHZ state of many atomic ensembles based on the dynamics of the atomic system of a single control atom and an atomic ensemble dispersively coupling with a cavity, where the control atom is illuminated by a highly detuned auxiliary classical field at the same time. The dynamics of the atomic system can be described by an effective Jaynes–Cummings model (JCM) with the atomic ensemble as the bosonic mode. The preparation of the entangled states is deterministic. Because the cavity is always in the vacuum state during the whole evolution process, our scheme is less sensitive to the cavity decay.

A large payload bidirectional quantum secure direct communication (BQSDC) protocol without information leakage is proposed, which is based on entanglement swapping between any two Greenberger–Horne–Zeilinger (GHZ) states. Two remote authorized parties, Alice and Bob, can safely exchange their individual secret messages without worrying about the information leakage problem. Our protocol uses a shared secret GHZ state to overcome the information leakage problem. The shared secret GHZ state plays two roles in the bidirectional communication process: on one hand, it lets Bob know the prepared initial state; on the other hand, it is used for encoding Bob's secret messages. Moreover, our protocol can transmit six bits of secret messages per round communication. Compared with those previous BQSDC protocols, the advantage of our protocol lies in having the following two characters simultaneously: on one hand, it overcomes the information leakage problem; one the other hand, its capacity is as high as six bits per round communication.

This paper offers a theoretical protocol for one-party controlled remote state preparation (RSP) of n-qubit states with minimum resources consumption. We are mainly focused on the case of the n-qubit state chosen from equatorial circle on a Bloch sphere. We use n - 1 EPR pairs and one GHZ state as quantum channel and show that only n + 1 cbits, n ebits and 2n + 1 qubits are consumed during the controlled RSP processing.

We present sufficient criteria for the entanglement of three-qubit states. For some special families of states, the criteria are also necessary for the entanglement. They are formulated as simple sets of inequalities for the mean values of certain observables defined as tensor products of Pauli matrices. The criteria are good indicators of the entanglement in the vicinity of three-qubit GHZ and W states and enjoy the capability of detecting the entangled states with positive partial transpositions. Furthermore, they improve the best known result for the case of W state mixed with the white noise. The efficiency of the criteria is illustrated through several examples.

A new concept of bidirectional quantum operation teleportation (BQOT) is proposed, which is essentially a union of the idea of quantum operation teleportation (QOT) and bidirectional quantum teleportation (QT). This means that Alice can transmit an unknown single-qubit unitary operation $U_A$ on the remote Bob’s quantum system; and at the same time, Bob can also transmit an arbitrary single-qubit unitary operation $U_B$ on Alice’s quantum system. In this paper, we present three BQOT schemes via different quantum channels. Furthermore, using these quantum channels, we investigate the BQOT in noisy environments, such as phase-damping noise and amplitude-damping noise. We considered the influence of the noises on the process of these three BQOT protocols through analytical derivation of the fidelity. Moreover, these three schemes are amply compared with each other from five aspects, i.e. quantum resource consumption, operation complexity, classical resource consumption, success probability and efficiency. It is found that these schemes can be realized deterministically and the first scheme is better than the other two schemes.

Recently, a novel Multi-layer Quantum Secret Sharing (MQSS) scheme based on GHZ state and generalized Bell measurement is presented in [X.-J. Wang, L.-X. An, X.-T. Yu and Z.-C. Zhang, Phys. Lett. A381(38) (2017) 3282.]. The novelty of the MQSS scheme is that a quantum secret can be shared by up to $3^n$ parties at the $n$th layer. In this paper, we show that the MQSS scheme can be significantly simplified and improved. The improved MQSS scheme is much easier to implement in practice and more efficient. In our improved scheme, the parties of the $n$th layer need not put their particles together to carry out the generalized Bell measurement, which is needed to share the secret to the next layer in the original scheme. Instead, each party only has to carry out local operations.

Quantum signature is a branch of quantum cryptography that draws on the design ideas of classic digital signatures, and uses the basic principles of quantum mechanics to achieve the integrity, authenticity and nonrepudiation of quantum information. Among them, arbitration quantum signature (AQS) plays a very important role. In this paper, we proposed an AQS protocol based on XOR encryption. Unlike other protocols, a quantum one-time pad encryption method or chain-type CNOT encryption method is abandoned. The proposed protocol is designed based on the three-particle GHZ state combined with the idea of classical XOR encryption, with CNOT operations used to encrypt quantum messages and quantum signatures. A security analysis of the proposed protocol reveals that the proposed protocol can satisfy the AQS requirements of unforgeability and nonrepudiation.