Deterministic secure quantum communication against collective-dephasing noise by using EPR pairs and auxiliary photons

A deterministic secure quantum communication against collective-dephasing noise is proposed. Alice constructs two sets of three-photon bases with EPR (Einstein-Podolsky-Rosen) pairs in the state |Ψ⁺〉 or |Ψ^-〉 and auxiliary single photons in the state |H〉. And then she sends them to Bob. Bob can get the secret message by his single-photon measurement outcomes and two public message strings from Alice if the quantum channel is secure. The scheme does not need photon storing technique and only single-photon measurement is necessary.     

可控量子秘密共享协议窃听检测虚警概率分析

对孙莹等提出的利用Greenberger-Horne-Zeilinger态实现的可控量子秘密共享协议Alice-Bob信道和Alice-Charlie信道窃听检测的虚警概率进行分析,指出该协议窃听检测虚警概率不为0的原因在于窃听检测测量基选择的随机性.然后,提出一种改进的利用Greenberger-HorneZeilinger态实现的可控量子秘密共享协议,以确定性的方式选择窃听检测的测量基.理论分析表明,改进的利用Greenberger-Horne-Zeilinger态实现的可控量子秘密共享协议不仅能够以原协议2倍的概率发现任何一个内部不可信方,从而具有更高的安全性,而且窃听检测虚警概率达到0.     

Quantum Secure Direct Communication by Using Three-Dimensional Hyperentanglement

We propose two schemes for realizing quantum secure direct communication (QSDC) by using a set of ordered two-photon three-dimensional hyperentangled states entangled in two degrees of freedom (DOFs) as quantum information channels. In the first scheme, the photons from Bob to Alice are transmitted only once. After insuring the security of the quantum channels, Bob encodes the secret message on his photons. Then Alice performs single-photon two-DOF Bell bases measurements on her photons. This scheme has better security than former QSDC protocols. In the second scheme, Bob transmits photons to Alice twice. After insuring the security of the quantum channels, Bob encodes the secret message on his photons. Then Alice performs two-photon Bell bases measurements on each DOF. The scheme has more information capacity than former QSDC protocols.     

Complex Wavelet Transform of the Two-mode Quantum States

By employing the bipartite entangled state representation and the technique of integration within an ordered product of operators, the classical complex wavelet transform of a complex signal function can be recast to a matrix element of the squeezing-displacing operator U ₂(μ, σ) between the mother wavelet vector 〈ψ| and the two-mode quantum state vector |f〉 to be transformed. 〈ψ|U ₂(μ, σ)|f〉 can be considered as the spectrum for analyzing the two-mode quantum state |f〉. In this way, for some typical two-mode quantum states, such as two-mode coherent state and two-mode Fock state, we derive the complex wavelet transform spectrum and carry out the numerical calculation. This kind of wavelet-transform spectrum can be used to recognize quantum states.     

Quantum Bit Commitment and the Reality of the Quantum State

Quantum bit commitment is insecure in the standard non-relativistic quantum cryptographic framework, essentially because Alice can exploit quantum steering to defer making her commitment. Two assumptions in this framework are that: (a) Alice knows the ensembles of evidence E corresponding to either commitment; and (b) system E is quantum rather than classical. Here, we show how relaxing assumption (a) or (b) can render her malicious steering operation indeterminable or inexistent, respectively. Finally, we present a secure protocol that relaxes both assumptions in a quantum teleportation setting. Without appeal to an ontological framework, we argue that the protocol’s security entails the reality of the quantum state, provided retrocausality is excluded.     

Side Channel Passive Quantum Key Distribution with One Uninformative State

In most of quantum key distribution schemes, real random number generators are required on both sides for preparation and measurement bases choice. In this paper, via entangled photon pairs, we present a side channel passive quantum key distribution scheme, in which random number generator is unneeded on the receiver side. On the sender Alice side, along with massive of signal photons, small amount of uninformative photons are randomly sent to her partner Bob for eavesdropper-presence testing and error estimation. While on the other side channel, without using random number generator Bob do not actively measure the income signals randomly in two non-orthogonal bases. Instead, he just passively register photon click events, in two settled symmetric (i.e.X) bases, and the raw key(click events) is the probable outcomes of a special quantum measurement module constructed by Alice and Bob. Further, security analysis and formulas of security bounds for this scheme is also investigated under reasonable assumptions. Our work shows that the uninformative state employed in this paper is powerful to fight against eavesdropper Eve.     

利用N粒子纠缠态的量子秘密共享

 为了高效实现多方之间的量子秘密共享,引入了一种纠缠度较高的N粒子纠缠态,并提出了利用该N粒子纠缠态在一方与（N-1）方之间形成共享秘密位串的方案.该方案在建立秘密位串的过程中,Alice对发送的粒子随机选择么正操作I和σx,并选择一部分粒子用于检测信道的安全|之后Alice根据（N-1）方选择的操作又选择了一部分粒子用于对参与者诚实度检测及信道安全检测.通过多次对窃听者的检测,很好地保证了信道的安全性及产生的秘密位串的可用性.最终在Alice及另外（N-1）方之间可形成n[1-(N-1)/2 N-1]/6个共享秘密位.     

Protecting Distribution Entanglement for Two-Qubit State Using Weak Measurement and Reversal

Protection of entanglement from disturbance of the environment is an essential task in quantum information processing. We investigate the effect of the weak measurement and reversal (WMR) on the protection of the entanglement for an arbitrarily entangled two-qubit pure state from these three typical quantum noisy channels, i.e., amplitude damping channel, phase damping channel and depolarizing quantum channel. Given the parameters of the Bell-like initial qubits’ state |ψ〉 = a|00〉 + d|11〉, it is found that the WMR operation indeed helps for protecting distributed entanglement from the above three noisy quantum channels. But for the Bell-like initial qubits’ state |?〉 = b|01〉 + c|10〉, the WMR operation only protects entanglement in the amplitude damping channel, not for the phase damping and depolarizing quantum channels. In addition, we discuss how the concurrence and the success probability behave with adjusting the weak or the reversal weak measurement strength.     

Authenticable Quantum Scheme for Secret Sharing Based on Local Distinguishability

The main defects of the existing quantum secret sharing schemes are as follows: (1) The identity of the secret sender cannot be confirmed. Receivers of shared secret information may be vulnerable to Trojan attacks; (2) If a malicious attacker Eve impersonates the identity of the receiver, she can finally obtain all the information of the secret that Alice shared; (3) In the process of secret recovery, it is necessary to transmit qubits among all participants involved in secret recovery. Sometimes, the same particle needs to be operated on by all participants to achieve secret sharing, which increases the possibility of eavesdropping and also increases the probability of errors. In this work, we proposed a quantum secret sharing scheme with authentication, the receiver performs corresponding operations on qubits of Greenberger-Horne-Zeilinger(GHZ) state based on the key string calculated by the shared identity number and random Error Correction Code(ECC), the secret sender can calculate the corresponding measurement basis(MB) through the information she has, and then inform the measurement party. This process realizes the mutual authentication between the sender and the receiver. It can protect against identity impersonation attacks, through the ECC verification, it also can resist intercept-resend attacks.

     

High-Capacity Three-Party Quantum Secret Sharing with Single Photons in Both the Polarization and the Spatial-Mode Degrees of Freedom

We present a high-capacity three-party quantum secret sharing (QSS) protocol with a sequence of single photons in both the polarization and the spatial-mode degrees of freedom. By inserting the boss Alice into the middle position between the two agents Bob and Charlie, our QSS protocol is secure in theory. The boss Alice chooses some unitary operations to encode her information on the single photons. It is interesting to point out the fact that Alice does not change the bases of the single photons which are used to carry the useful information about the private key, which improves its success probability for obtaining a private key. Compared with the QSS protocol by Zhou et al. (Chin. Phys. Lett. 24, 2181 (2007)), our QSS protocol has a higher capacity without increasing the difficulty of its implementation in experiment as each correlated photon can carry two bits of useful information. Compared with those QSS protocols based on entangled photon pairs and Bell-state measurements, our QSS protocol is more feasible as it does not require the complete Bell-state analysis which is not easy with linear optics. We give out the setup for the implementation of our QSS protocol with linear optical elements.     

Efficient Three-Party Quantum Secret Sharing with Single Photons

A scheme for three-party quantum secret sharing of a private key is presented with single photons. The agent Bob first prepares a sequence of single photons with two biased bases and then sends them to the boss Alice who checks the security of the transmission with measurements and produces some decoy photons by rearranging the orders of some sample photons. Alice encodes her bits with two unitary operations on the photons and then sends them to the other agent. The security of this scheme is equivalent to that in the modified Bennett Brassard 1984 quantum key distribution protocol. Moreover, each photon can carry one bit of the private key and the intrinsic efficiency for qubits and the total efficiency both approach the maximal value 100% when the number of the bits in the key is very large.     

Probabilistic Quantum Information Splitting Based on the Non-maximally Entangled Four-Qubit State

In this paper, we propose a scheme for quantum information splitting based on the non-maximally entangled four-qubit state in order to realize the splitting of the specific two-qubit state |ψ〉 _{A B} =x|00〉+y|11〉. The information splitter will safely share an state to the receiver with help of the controller. Through introducing an auxiliary system and applying several appropriate unitary transformations the information receiver can reconstruct the original state sent by the information splitter. Due to the non-maximally entangled four-qubit state, the total probability that the receiver obtains the original information is P. Furthermore, we discuss the relationship between the successful splitting probability and the concurrence of the entangled state and get a specific expression. In addition, the scheme is tested against external and internal attacks, and we define a function to characterise the security with the concurrence of the entanglement.     

具有双向认证功能的量子秘密共享方案

利用两粒子纠缠态作为经典信息的载体,结合Hash函数和量子本地操作提出了一种可以实现双向认证功能的量子秘密共享方案,并且分析了它的安全性. 这种方案的安全性基于秘密共享双方的认证密钥和传输过程中粒子排列次序的保密. 若不考虑认证和窃听检测所消耗的粒子,平均1个Bell态共享2 bit经典信息. 关键词： 量子秘密共享 认证密钥 量子双向认证 两粒子量子纠缠     

Dynamic(2, 3) Threshold Quantum Secret Sharing of Secure Direct Communication

In this paper, we show that a(2, 3) discrete variable threshold quantum secret sharing scheme of secure direct communication can be achieved based on recurrence using the same devices as in BB84. The scheme is devised by first placing the shares of smaller secret pieces into the shares of the largest secret piece, converting the shares of the largest secret piece into corresponding quantum state sequences, inserting nonorthogonal state particles into the quantum state sequences with the purpose of detecting eavesdropping, and finally sending the new quantum state sequences to the three participants respectively. Consequently, every particle can on average carry up to 1.5-bit messages due to the use of recurrence. The control codes are randomly prepared using the way to generate fountain codes with pre-shared source codes between Alice and Bob, making three participants can detect eavesdropping by themselves without sending classical messages to Alice. Due to the flexible encoding, our scheme is also dynamic, which means that it allows the participants to join and leave freely.     

Quantum Authencryption with Two-Photon Entangled States for Off-Line Communicants

In this paper, a quantum authencryption protocol is proposed by using the two-photon entangled states as the quantum resource. Two communicants Alice and Bob share two private keys in advance, which determine the generation of two-photon entangled states. The sender Alice sends the two-photon entangled state sequence encoded with her classical bits to the receiver Bob in the manner of one-step quantum transmission. Upon receiving the encoded quantum state sequence, Bob decodes out Alice’s classical bits with the two-photon joint measurements and authenticates the integrity of Alice’s secret with the help of one-way hash function. The proposed protocol only uses the one-step quantum transmission and needs neither a public discussion nor a trusted third party. As a result, the proposed protocol can be adapted to the case where the receiver is off-line, such as the quantum E-mail systems. Moreover, the proposed protocol provides the message authentication to one bit level with the help of one-way hash function and has an information-theoretical efficiency equal to 100 %.     

Laguerre-Polynomial-Weighted Two-Mode Squeezed State

We propose a new optical field named Laguerre-polynomial-weighted two-mode squeezed state. We find that such a state can be generated by passing the l-photon excited two-mode squeezed vacuum state C_la^?lS₂|00〉 through an single-mode amplitude damping channel. Physically, this paper actually is concerned what happens when both excitation and damping of photons co-exist for a two-mode squeezed state, e.g., dessipation of photon-added two-mode squeezed vacuum state. We employ the summation method within ordered product of operators and a new generating function formula about two-variable Hermite polynomials to proceed our discussion.     

Background Independent Quantum Mechanics,Metric of Quantum States,and Gravity: A Comprehensive Perspective

This paper presents a comprehensive perspective of the metric of quantum states with a focus on the geometry in the background independent quantum mechanics. We also explore the possibilities of geometrical formulations of quantum mechanics beyond the quantum state space and Kähler manifold. The metric of quantum states in the classical configuration space with the pseudo-Riemannian signature and its possible applications are explored. On contrary to the common perception that a metric for quantum state can yield a natural metric in the configuration space when the limit ?→0, we obtain the metric of quantum states in the configuration space without imposing the limiting condition ?→0. Here Planck’s constant ? is absorbed in the quantity like Bohr radii \(\frac{1}{2mZ\alpha}\sim a_{0}\). While exploring the metric structures associated with Hydrogen like atom, we witness another interesting finding that the invariant lengths appear in the multiple of Bohr’s radii as: ds ²=a ₀ ² (? Ψ)².     

High-Dimensional Circular Quantum Secret Sharing Using Orbital Angular Momentum

Quantum secret sharing is to distribute secret message securely between multi-parties. Here exploiting orbital angular momentum (OAM) state of single photons as the information carrier, we propose a high-dimensional circular quantum secret sharing protocol which increases the channel capacity largely. In the proposed protocol, the secret message is split into two parts, and each encoded on the OAM state of single photons. The security of the protocol is guaranteed by the laws of non-cloning theorem. And the secret messages could not be recovered except that the two receivers collaborated with each other. Moreover, the proposed protocol could be extended into high-level quantum systems, and the enhanced security could be achieved.     

Three-step semiquantum secure direct communication protocol

Quantum secure direct communication is the direct communication of secret messages without need for establishing a shared secret key first. In the existing schemes, quantum secure direct communication is possible only when both parties are quantum. In this paper, we construct a three-step semiquantum secure direct communication (SQSDC) protocol based on single photon sources in which the sender Alice is classical. In a semiquantum protocol, a person is termed classical if he (she) can measure, prepare and send quantum states only with the fixed orthogonal quantum basis {|0〉, |1〉}. The security of the proposed SQSDC protocol is guaranteed by the complete robustness of semiquantum key distribution protocols and the unconditional security of classical one-time pad encryption. Therefore, the proposed SQSDC protocol is also completely robust. Complete robustness indicates that nonzero information acquired by an eavesdropper Eve on the secret message implies the nonzero probability that the legitimate participants can find errors on the bits tested by this protocol. In the proposed protocol, we suggest a method to check Eves disturbing in the doves returning phase such that Alice does not need to announce publicly any position or their coded bits value after the photons transmission is completed. Moreover, the proposed SQSDC protocol can be implemented with the existing techniques. Compared with many quantum secure direct communication protocols, the proposed SQSDC protocol has two merits: firstly the sender only needs classical capabilities; secondly to check Eves disturbing after the transmission of quantum states, no additional classical information is needed.     

Quantum Secure Direct Communication with Authentication Expansion UsingSingle Photons

In this paper we propose two quantum secure direct communication (QSDC) protocols with authentication. The authentication key expansion method is introduced to improve the life of the keys with security. In the first scheme, the third party, called Trent is introduced to authenticate the users that participate in the communication. He sends the polarized photons in blocks toauthenticate communication parties Alice and Bob using the authentication keys. In the communication process, polarized single photons are used to serve as the carriers, which transmit the secret messages directly. The second QSDC process with authentication between two parties is also discussed.