Quantum secure direct communication via partially entangled states

We present in this paper a quantum secure direct communication （QSDC） protocol by using partially entangled states. In the scheme a third party （Trent） is introduced to authenticate the participants. After authentication, Alice can directly, deterministically and successfully send a secret message to Bob. The security of the scheme is also discussed and confirmed.

Quantum secure direct communication with quantum encryption based on pure entangled states

This paper presents a scheme for quantum secure direct communication with quantum encryption. The two authorized users use repeatedly a sequence of the pure entangled pairs （quantum key） shared for encrypting and decrypting the secret message carried by the travelling photons directly. For checking eavesdropping, the two parties perform the single-photon measurements on some decoy particles before each round. This scheme has the advantage that the pure entangled quantum signal source is feasible at present and any eavesdropper cannot steal the message.

Quantum Secure Direct Communication with Four-Particle Genuine Entangled State and Dense Coding

A quantum secure direct communication scheme using dense coding is proposed.At first,the sender (Alice)prepares four-particle genuine entangled states and shares them with the receiver (Bob) by sending two particles in eachentangled state to him.Secondly,Alice encodes secret information by performing the unitary transformations on herparticles and transmits them to Bob.Finally,Bob performs the joint measurements on his particles to decode the secretinformation.The two-step security test guarantees the security of communication.

Quantum Secure Direct Communication Using Six-Particle Maximally Entangled States and Teleportation

The sender shares six-particle maximally entangled states as quantum channel with the receiver. If the quantum channel is secure, the sender performs projective measurements and tells the measurement outcome to the receiver. The receiver performs the unitary transformations and makes projective measurements on his particles to obtain the secret information. Using teleportation, the transmission of three-qubit secret information can be completed in each quantum channel

Improvement on Quantum Secure Direct Communication with W State in Noisy Channel

An improvement （Y-protocol） [Commun. Theor. Phys. 49 （2008） 103] on the quantum secure direct communication with W state （C-protocol） [Chin. Phys. Lett. 23 （2006） 290] is proposed by Yuan et al. The quantum bit error rate induced by eavesdropper is 4.17% in C-protocol and 6.25% in Y-protocoL In this paper, another improvement on C-protocol is given. The quantum bit error rate of the eavesdropping will increase to 8.75%, which is 1.1 times larger than that in C-protocol and 0.4 times larger than that in Y-protocol.

Robust quantum secure direct communication and authentication protocol against decoherence noise based on six-qubit DF state

By using six-qubit decoherence-free （DF） states as quantum carriers and decoy states, a robust quantum secure direct communication and authentication （QSDCA） protocol against decoherence noise is proposed. Four six-qubit DF states are used in the process of secret transmission, however only the ｜0＇〉 state is prepared. The other three six-qubit DF states can be obtained by permuting the outputs of the setup for ｜0＇〉. By using the ｜0＇〉 state as the decoy state, the detection rate and the qubit error rate reach 81.3%, and they will not change with the noise level. The stability and security are much higher than those of the ping-pong protocol both in an ideal scenario and a decoherence noise scenario. Even if the eavesdropper measures several qubits, exploiting the coherent relationship between these qubits, she can gain one bit of secret information with probability 0.042.

Quantum Secure Direct Communication Protocol with Mutual Authentication Based on Single Photons and Bell States

Quantum secure direct communication(QSDC)can transmit secret messages directly from one user to another without first establishing a shared secret key,which is different from quantum key distribution.In this paper,we propose a novel quantum secure direct communication protocol based on signal photons and Bell states.Before the execution of the proposed protocol,two participants Alice and Bob exchange their corresponding identity IDA and IDB through quantum key distribution and keep them secret,respectively.Then the message sender,Alice,encodes each secret message bit into two single photons(|01>or|10>)or a Bell state(1|φ^(+)>=1/√2(|0>|-|1>1>)),and composes an ordered secret message sequence.To insure the security of communication,Alice also prepares the decoy photons and inserts them into secret message sequence on the basis of the values of IDA and IDB.By the secret identity IDA and IDB,both sides of the communication can check eavesdropping and identify each other.The proposed protocol not only completes secure direct communication,but also realizes the mutual authentication.The security analysis of the proposed protocol is presented in the paper.The analysis results show that this protocol is secure against some common attacks,and no secret message leaks even if the messages are broken.Compared with the two-way QSDC protocols,the presented protocol is a one-way quantum communication protocol which has the immunity to Trojan horse attack.Furthermore,our proposed protocol can be realized without quantum memory.

Quantum communication for satellite-to-ground networks with partially entangled states

To realize practical wide-area quantum communication,a satellite-to-ground network with partially entangled states is developed in this paper.For efficiency and security reasons,the existing method of quantum communication in distributed wireless quantum networks with partially entangled states cannot be applied directly to the proposed quantum network.Based on this point,an efficient and secure quantum communication scheme with partially entangled states is presented.In our scheme,the source node performs teleportation only after an end-to-end entangled state has been established by entanglement swapping with partially entangled states.Thus,the security of quantum communication is guaranteed.The destination node recovers the transmitted quantum bit with the help of an auxiliary quantum bit and specially defined unitary matrices.Detailed calculations and simulation analyses show that the probability of successfully transferring a quantum bit in the presented scheme is high.In addition,the auxiliary quantum bit provides a heralded mechanism for successful communication.Based on the critical components that are presented in this article an efficient,secure,and practical wide-area quantum communication can be achieved.

Quantum Secure Direct Communication and Quantum Sealed-Bid Auction with EPR Pairs

I present a new protocol for three-party quantum secure direct communication （QSDC） with a set of ordered M Einstein-Podolsky-Rosen （EPR） pairs. In the scheme, by performing two unitary operations and Bell state measurements, it is shown that the three legitimate parties can exchange their respective secret message simultaneously. Then I modify it for an experimentally feasible and secure quantum sealed-bid auction （QSBD） protocol. Furthermore, I also analyze th^ecurity of the protocol, and the scheme is proven to be secure against the intercept-and-resend attack, the disturbancb attack and the entangled-and-measure attack.

Measurement-device-independent one-step quantum secure direct communication

The one-step quantum secure direct communication(QSDC)(Sci.Bull.67,367(2022))can effectively simplify QSDC’s operation and reduce message loss.For enhancing its security under practical experimental condition,we propose two measurement-device-independent(MDI)one-step QSDC protocols,which can resist all possible attacks from imperfect measurement devices.In both protocols,the communication parties prepare identical polarization-spatial-mode two-photon hyperentangled states and construct the hyperentanglement channel by hyperentanglement swapping.The first MDI one-step QSDC protocol adopts the nonlinear-optical complete hyperentanglement Bell state measurement(HBSM)to construct the hyperentanglement channel,while the second protocol adopts the linear-optical partial HBSM.Then,the parties encode the photons in the polarization degree of freedom and send them to the third party for the hyperentanglementassisted complete polarization Bell state measurement.Both protocols are unconditionally secure in theory.The simulation results show the MDI one-step QSDC protocol with complete HBSM attains the maximal communication distance of about354 km.Our MDI one-step QSDC protocols may have potential applications in the future quantum secure communication field.

Robust Quantum Secure Direct Communication and Deterministic Secure Quantum Communication over Collective Dephasing Noisy Channel

We propose two schemes for quantum secure direct communication (QSDC) and deterministic securequantum communication (DSQC) over collective dephasing noisy channel.In our schemes,four special two-qubit statesare used as the quantum channel.Since these states are unchanged through the collective dephasing noisy channel,the effect of the channel noise can be perfectly overcome.Simultaneously,the security against some usual attacks canbe ensured by utilizing the various checking procedures.Furthermore,these two schemes are feasible with present-daytechnique.

High-capacity device-independent quantum secure direct communication based on hyper-encoding

Quantum secure direct communication(QSDC)can directly transmit secret messages through quantum channel without keys.Device-independent(DI)QSDC guarantees the message security relying only on the observation of the Bell-inequality violation,but not on any detailed description or trust of the devices'inner workings.Compared with conventional QSDC,DI-QSDC has relatively low secret message capacity.To increase DI-QSDC's secret messages capacity,we propose a high-capacity DI-QSDC protocol based on the hyper-encoding technique.The total message leakage rate of our DI-QSDC protocol only relies on the most robust degree of freedom.We provide the numerical simulation of its secret message capacity altered with the communication distance.Our work serves as an important step toward thefurther development of DI-QSDC systems.

Quantum secure direct communication with hybrid entanglement

Quantum secure direct communication(QSDC)can transmit secret messages without keys,making it an important branch of quantum communication.We present a hybrid entanglement-based quantum secure direct communication(HE-QSDC)protocol with simple linear optical elements,combining the benefits of both continuous variables(CV)and discrete variables(DV)encoding.We analyze the security and find that the QSDC protocol has a positive security capacity when the bit error rate is less than 0.073.Compared with previous DV QSDC protocols,our protocol has higher communication efficiency due to performing nearly deterministic Bell-state measurement.On the other hand,compared with CV QSDC protocol,this protocol has higher fidelity with largeα.Based on these advantages,our protocol may provide an alternative approach to realize secure communication.

Deterministic hierarchical joint remote state preparation with six-particle partially entangled state

In this paper, we present a novel scheme for hierarchical joint remote state preparation（HJRSP） in a deterministic manner, where two senders can jointly and remotely prepare an arbitrary single-qubit at three receivers＇ port. A six-particle partially entangled state is pre-shared as the quantum channel. There is a hierarchy among the receivers concerning their powers to reconstruct the target state. Due to various unitary operations and projective measurements, the unit success probability can always be achieved irrespective of the parameters of the pre-shared partially entangled state.

Controlled Secure Direct Communication Protocol via the Three-Qubit Partially Entangled Set of States

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.

Three-party quantum secret sharing of secure direct communication based on χ-type entangled states

Based on x-type entangled states and the two-step protocol [Deng F G, Long G L and Liu X S 2003 Phys. Rev. A 68 042317], a quantum secret sharing protocol of secure direct communication based on x-type entangled states ｜X00〉3214 is proposed. Using some interesting entanglement properties of this state, the agent entirety can directly obtain the secret message from the message sender only if they collaborate together. The security of the scheme is also discussed.

Quantum secure direct communication with cluster states

A quantum secure direct communication protocol with cluster states is proposed.Compared with the deterministic secure quantum communication protocol with the cluster state proposed by Yuan and Song(Int.J.Quant.Inform.,2009,7:689),this protocol can achieve higher intrinsic efficiency by using two-step transmission.The implementation of this protocol is also discussed.

Controlled Secure Quantum Communication Using Pure Entangled W Class States

We present a controlled secure quantum communication protocol using non-maximally （pure） entangled W states first, and then discuss the basic requirements for a real quantum communication. We show that the authorized two users can exchange their secret messages with the help of the controller after purifying the non-maximally entangled states quantum channel unconditionally securely and simultaneously. Our quantum communication protocol seems even more feasible within present technologies.

Experimental long-distance quantum secure direct communication

Quantum secure direct communication(QSDC) is an important quantum communication branch, which realizes the secure information transmission directly without encryption and decryption processes.Recently, two table-top experiments have demonstrated the principle of QSDC. Here, we report the first long-distance QSDC experiment, including the security test, information encoding, fiber transmission and decoding. After the fiber transmission of 0.5 km, quantum state fidelities of the two polarization entangled Bell states are 91% and 88%, respectively, which are used for information coding. We theoretically analyze the performance of the QSDC system based on current optical communication technologies,showing that QSDC over fiber links of several tens kilometers could be expected. It demonstrates the potential of long-distance QSDC and supports its future applications on quantum communication networks.

One-step device-independent quantum secure direct communication

Device-independent quantum secure direct communication(DI-QSDC)can relax the security assumptions about the devices’internal working,and effectively enhance QSDC’s security.In this paper,we put forward the first hyperentanglement-based one-step DI-QSDC protocol.In this protocol,the communication parties adopt the nonlocal hyperentanglement-assisted complete Bell state analysis,which enables the photons to transmit in the quantum channel for only one round.The one-step DI-QSDC can directly transmit 2 bits of messages by a hyperentangled photon pair,and is unconditionally secure in theory.Compared with the original DI-QSDC protocol(Sci.Bull.65,12(2020)),the one-step DI-QSDC protocol can simplify the experiment and reduce the message loss.In particular,with the help of the hyperentanglement heralded amplification and the hyperentanglement purification,the message loss and the message error caused by the channel noise can be completely eliminated,and the communication distance can be largely extended.By using the photon source with a repetition rate of 10 GHz,the one-step DI-QSDC’s secret message capacity under 50 km communication distance achieves about 7 bit/s with the initial fidelity in each degree of freedom of 0.8.Combined with the quantum repeater,it is possible for researchers to realize the one-step DI-QSDC with an arbitrarily long distance.