Recently,some blind quantum signature(BQS) protocols have been proposed.But the previous schemes have security and efficiency problems.Based on the entangled Greenberger-Horne-Zeilinger(GHZ) states,a new weak BQS protocol is proposed.Compared with some existing schemes,our protocol has 100% efficiency.Besides,the protocol is simple and easy to implement.The security of the protocol is guaranteed by the correlation of the GHZ particles held by each participant.In our protocol,the signatory is kept blind from the content of the message.According to the security analysis,the signatory cannot disavowal his/her signature while the signature cannot be forged by others.
In this paper,we first re-examine the previous protocol of controlled quantum secure direct communication of Zhang et al.’s scheme,which was found insecure under two kinds of attacks,fake entangled particles attack and disentanglement attack.Then,by changing the party of the preparation of cluster states and using unitary operations,we present an improved protocol which can avoid these two kinds of attacks.Moreover,the protocol is proposed using the three-qubit partially entangled set of states.It is more efficient by only using three particles rather than four or even more to transmit one bit secret information.Given our using state is much easier to prepare for multiqubit states and our protocol needs less measurement resource,it makes this protocol more convenient from an applied point of view.
A universal entangler is a very powerful fault-tolerant entangling device for generating quantum entanglements from any joint states. Our paper aims to address the construction of universal entanglers. We prove that universal entanglers may be obtained from random unitary gates according to the Harr measure. The success probability is close to 1 for large system spaces. This result represents the typical density of entanglement subspaces in large state spaces. It also partially solves an open problem of universal bipartite entanglers and is explained by some experiment simulations.
WANG FengLUO MingXingCHEN XiuBoYANG YiXianWANG XiaoJun
In this paper,we first propose a hidden rule among the secure message,the initial tensor product of two Bell states and the final tensor product when respectively applying local unitary transformations to the first particle of the two initial Bell states,and then present a high-efficiency quantum steganography protocol under the control of the hidden rule.In the proposed quantum steganography scheme,a hidden channel is established to transfer a secret message within any quantum secure direct communication(QSDC) scheme that is based on 2-level quantum states and unitary transformations.The secret message hiding/unhiding process is linked with the QSDC process only by unitary transformations.To accurately describe the capacity of a steganography scheme,a quantitative measure,named embedding efficiency,is introduced in this paper.The performance analysis shows that the proposed steganography scheme achieves a high efficiency as well as a good imperceptibility.Moreover,it is shown that this scheme can resist all serious attacks including the intercept-resend attack,measurement-resend attack,auxiliary particle attack and even the Denial of Service attack.To improve the efficiency of the proposed scheme,the hidden rule is extended based on the tensor product of multiple Bell states.
Two deterministic schemes are proposed to realize the assisted clone of an unknown four-particle entangled clustertype state.The schemes include two stages.The first stage requires teleportation via maximal entanglement as the quantum channel.In the second stages of the protocols,two novel sets of mutually orthogonal basis vectors are constructed.With the assistance of the preparer through a four-particle or two-step two-particle projective measurement under these bases,the perfect copy of an original state can be produced.Comparing with the previous protocols which produce the unknown state and its orthogonal complement state at the site of the sender,the proposed schemes generate the unknown state deterministically.
Quantum steganography that utilizes the quantum mechanical effect to achieve the purpose of information hiding is a popular topic of quantum information.Recently,El Allati et al.proposed a new quantum steganography using the GHZ4 state.Since all of the 8 groups of unitary transformations used in the secret message encoding rule change the GHZ4 state into 6 instead of 8 different quantum states when the global phase is not considered,we point out that a 2-bit instead of a 3-bit secret message can be encoded by one group of the given unitary transformations.To encode a 3-bit secret message by performing a group of unitary transformations on the GHZ4 state,we give another 8 groups of unitary transformations that can change the GHZ4 state into 8 different quantum states.Due to the symmetry of the GHZ4 state,all the possible 16 groups of unitary transformations change the GHZ4 state into 8 different quantum states,so the improved protocol achieves a high efficiency.
Using entanglement swapping of high-level Bell states, we first derive a covert layer between the secret message and the possible output results of the entanglement swapping between any two generalized Bell states, and then propose a novel high-efficiency quantum information hiding protocol based on the covert layer. In the proposed scheme, a covert channel can be built up under the cover of a high-level quantum secure direct communication(QSDC) channel for securely transmitting secret messages without consuming any auxiliary quantum state or any extra communication resource. It is shown that this protocol not only has a high embedding efficiency but also achieves a good imperceptibility as well as a high security.
Rational participants want to maximize their benefits.The protocol with rational participants will be more realistic than the protocol with honest,semi-honest and dishonest participants.We research the rational non-hierarchical quantum state sharing in this paper.General steps of some known quantum state sharing protocol are summarized.Based on these steps,a new rational protocol is proposed.It means that lots of common protocols could be modified to rational protocols.Our protocol is widely applicable.Analyses show that the proposed protocol is rational and secure.It is also all-win for agents.Furthermore,number of deceiving agents is considered to redefine the utilities of agents.
