Faithful quantum secure direct communication protocol against collective noise

An improved quantum secure direct communication (QSDC) protocol is proposed in this paper.Blocks of entangled photon pairs are transmitted in two steps in which secret messages are transmitted directly.The single logical qubits and unitary operations under decoherence free subspaces are presented and the generalized Bell states are constructed which are immune to the collective noise.Two steps of qubit transmission are used in this protocol to guarantee the security of communication.The security of the protocol against various attacks are discussed.     

Faithful deterministic secure quantum communication and authentication protocol based on hyperentanglement against collective noise

Higher channel capacity and security are difficult to reach in a noisy channel. The loss of photons and the distortion of the qubit state are caused by noise. To solve these problems, in our study, a hyperentangled Bell state is used to design faithful deterministic secure quantum communication and authentication protocol over collective-rotation and collective-dephasing noisy channel, which doubles the channel capacity compared with using an ordinary Bell state as a carrier; a logical hyperentangled Bell state immune to collective-rotation and collective-dephasing noise is constructed. The secret message is divided into several parts to transmit, however the identity strings of Alice and Bob are reused. Unitary operations are not used.     

Quantum key distribution protocols with six-photon states against collective noise

Either collective-dephasing noise or collective-rotation noise is considered, two efficient quantum key distribution protocols are presented. With eight product states of three EPR pairs, two bits of secret key can be distributed successfully in each six-photon state. Comparing with the four-photon secret key distribution protocols, the security is also enhanced by using three sets (or more) of measurement bases.     

Three-particle QKD protocol against a collective noise

The research on decoherence-free subspace has both theoretical and practical significance. DFS is a subspace of quantum system states which is robust against a specific form of decoherence. The method of constructing DFS based algebra, which is different from the way based on the special Bell states, is introduced. Then a three-particle QKD protocol against collective-bit flipping noise is presented according to this method. Finally, we make a security analysis of our protocol.     

Fault tolerant controlled quantum dialogue against collective noise

Quantum system is inevitably affected by the external environment in the real world. Two controlled quantum dialogue protocols are put forward based on logical χ-type states under collective noise environment. One is against collectivedephasing noise, while the other is against collective-rotation noise. Compared with existing protocols, there exist several outstanding advantages in our proposed protocols: Firstly, the χ-type state is utilized as quantum channels, it possesses better entanglement properties than GHZ state, W state as well as cluster state, which make it difficult to be destroyed by local operations. Secondly, two kinds of logical χ-type states are constructed by us in theory, which can be perfectly immune to the effects of collective noise. Thirdly, the controller can be offline after quantum distribution and permission announcement, without waiting for all the participants to complete the information coding. Fourthly, the security analysis illuminates that our protocols can not only be free from the information leakage, but also resist against the interceptand-resend attack, the entanglement-and-measure attack, the modification attack, the conspiring attack, and especially the dishonest controller's attacks.     

Information leakage resistant quantum dialogue against collective noise

In this paper,two information leakage resistant quantum dialogue(QD)protocols over a collective-noise channel are proposed.Decoherence-free subspace(DFS)is used to erase the influence from two kinds of collective noise,i.e.,collective-dephasing noise and collective-rotation noise,where each logical qubit is composed of two physical qubits and free from noise.In each of the two proposed protocols,the secret messages are encoded on the initial logical qubits via two composite unitary operations.Moreover,the single-photon measurements rather than the Bell-state measurements or the more complicated measurements are needed for decoding,making the two proposed protocols easier to implement.The initial state of each logical qubit is privately shared between the two authenticated users through the direct transmission of its auxiliary counterpart.Consequently,the information leakage problem is avoided in the two proposed protocols.Moreover,the detailed security analysis also shows that Eve’s several famous active attacks can be effectively overcome,such as the Trojan horse attack,the intercept-resend attack,the measure-resend attack,the entangle-measure attack and the correlation-elicitation(CE)attack.     

Fault tolerant channel-encrypting quantum dialogue against collective noise

In this paper,two fault tolerant channel-encrypting quantum dialogue(QD)protocols against collective noise are presented.One is against collective-dephasing noise,while the other is against collective-rotation noise.The decoherent-free states,each of which is composed of two physical qubits,act as traveling states combating collective noise.Einstein-Podolsky-Rosen pairs,which play the role of private quantum key,are securely shared between two participants over a collective-noise channel in advance.Through encryption and decryption with private quantum key,the initial state of each traveling two-photon logical qubit is privately shared between two participants.Due to quantum encryption sharing of the initial state of each traveling logical qubit,the issue of information leakage is overcome.The private quantum key can be repeatedly used after rotation as long as the rotation angle is properly chosen,making quantum resource economized.As a result,their information-theoretical efficiency is nearly up to 66.7%.The proposed QD protocols only need single-photon measurements rather than two-photon joint measurements for quantum measurements.Security analysis shows that an eavesdropper cannot obtain anything useful about secret messages during the dialogue process without being discovered.Furthermore,the proposed QD protocols can be implemented with current techniques in experiment.     

Insulating one house against aircraft noise

A house near Manchester Airport has been insulated against aircraft noise and measurements were made to establish the usefulness of different methods. It was found that domestic quality dual glazing gives an insulation of about 40 dB(A), glass fibre laid in the loft gives an insulation increase of about 4 dB(A) compared with the bare ceiling, and extra boarding in the loft gives no benefit, probably because the existing lath-and-plaster ceiling is fairly heavy and so gives adequate insulation. The insulation can be increased further by installing heavy glazing, but that would normally be prohibitively expensive.     

Fault tolerant three-party quantum secret sharing against collective noise

We present two robust three-party quantum secret sharing protocols against two kinds of collective noise. Each logical qubit is made up of two physical qubits and is invariant under a collective noise. The two agents encode their message on each logical qubit with two unitary physical operations on two physical qubits. As each logical qubit received by each agent can carry two bits of information and the classical information exchanged is reduced largely, these protocols have a high intrinsic efficiency. Moreover, the boss Alice can read out her agents' information with two Bell-state measurements on each four-qubit system, not four-photon joint measurements.     

Dephasing of a superconducting qubit induced by photon noise

We have studied the dephasing of a superconducting flux qubit coupled to a dc-SQUID based oscillator. By varying the bias conditions of both circuits we were able to tune their effective coupling strength. This allowed us to measure the effect of such a controllable and well-characterized environment on the qubit coherence. We can quantitatively account for our data with a simple model in which thermal fluctuations of the photon number in the oscillator are the limiting factor. In particular, we observe a strong reduction of the dephasing rate whenever the coupling is tuned to zero. At the optimal point we find a large spin-echo decay time of .     

Arbitrated quantum signature of classical messages against collective amplitude damping noise

We give an arbitrated signature protocol of classical messages over a collective amplitude damping channel. We analyze its security and prove that it is secure over such a noisy quantum channel even if the arbitrator is compromised. The involvement of the arbitrator is also an appealing advantage in the implementation of a practical quantum distributed communication network.     

New arbitrated quantum signature of classical messages against collective amplitude damping noise

Recently, Chong et al. [Opt. Comm. 284, (2011) 893-895] pointed out that a dishonest party in Yang and Wen's arbitrated quantum signature scheme [Opt. Comm. 283, (2010) 3198-3201] is able to reveal the other party's secret key without being detected by using the Trojan-horse attacks. However, the solution to avoid the attack still remains open. This work further points out that in Yang and Wen's scheme, the arbitrator is unable to arbitrate the dispute between two users. Consequently, a user can deny that he/she has signed or verified a signature without performing a Trojan-horse attack. A solution is proposed to solve this problem as well as the open problem mentioned earlier.     

Fault tolerant quantum secure direct communication with quantum encryption against collective noise

We present two novel quantum secure direct communication(QSDC) protocols over different collective-noise channels.Different from the previous QSDC schemes over collective-noise channels,which are all source-encrypting protocols,our two protocols are based on channel-encryption.In both schemes,two authorized users first share a sequence of EPR pairs as their reusable quantum key.Then they use their quantum key to encrypt and decrypt the secret message carried by the decoherence-free states over the collective-noise channel.In theory,the intrinsic efficiencies of both protocols are high since there is no need to consume any entangled states including both the quantum key and the information carriers except the ones used for eavesdropping checks.For checking eavesdropping,the two parties only need to perform two-particle measurements on the decoy states during each round.Finally,we make a security analysis of our two protocols and demonstrate that they are secure.     

Remote preparation of a single-mode photonic qubit by measuring field quadrature noise

An electromagnetic field quadrature measurement, performed on one of the modes of the nonlocal single-photon state alpha|1,0>-beta|0,1>, collapses it into a superposition of the single-photon and vacuum states in the other mode. We use this effect to implement remote preparation of arbitrary single-mode photonic qubits conditioned on observation of a preselected quadrature value. The preparation efficiency of the resulting qubit can be higher than that of the initial single photon.     

Fault tolerant deterministic secure quantum communication using logical Bell states against collective noise

This study proposes two novel fault tolerant deterministic secure quantum communication(DSQC) schemes resistant to collective noise using logical Bell states. Either DSQC scheme is constructed based on a new coding function, which is designed by exploiting the property of the corresponding logical Bell states immune to collective-dephasing noise and collective-rotation noise, respectively. The secret message can be encoded by two simple unitary operations and decoded by merely performing Bell measurements, which can make the proposed scheme more convenient in practical applications.Moreover, the strategy of one-step quanta transmission, together with the technique of decoy logical qubits checking not only reduces the influence of other noise existing in a quantum channel, but also guarantees the security of the communication between two legitimate users. The final analysis shows that the proposed schemes are feasible and robust against various well-known attacks over the collective noise channel.     

Controlled quantum key distribution with three-photon polarization-entangled states via the collective noise channel

Using three-photon polarization-entangled GHZ states or W states, we propose controlled quantum key distribution protocols for circumventing two main types of collective noise, collective dephasing noise, or collective rotation noise. Irrespective of the number of controllers, a three-photon state can generate a one-bit secret key. The storage technique of quantum states is dispensable for the controller and the receiver, and it therefore allows performing the process in a more convenient mode. If the photon cost in a security check is disregarded, then the efficiency theoretically approaches unity.     

Geometric phase of a qubit driven by a phase noise laser under non-Markovian dynamics

Robustness of the geometric phase (GP) with respect to the environmental effects is a basic condition for an effective quantum computation. Here, we study quantitatively the GP of a two-level atom system driven by a phase noise laser under non-Markovian dynamics in terms of different parameters involved in the whole system. We find that with the change of the damping coupling, the GP is very sensitive to its properties exhibiting long collapse and revival phenomena, which play a significant role in enhancing the stabilization and control of the system dynamics. Moreover, we show that the GP can be considered as a tool for testing and characterizing the nature of the qubit–environment coupling. Due to the significance of how a system is quantum correlated with its environment in the construction of a scalable quantum computer, the entanglement dynamics between the qubit with its environment under external classical noise is evaluated and investigated during the time evolution.     

Security of a practical semi-device-independent quantum key distribution protocol against collective attacks

Similar to device-independent quantum key distribution(DI-QKD), semi-device-independent quantum key distribution(SDI-QKD) provides secure key distribution without any assumptions about the internal workings of the QKD devices.The only assumption is that the dimension of the Hilbert space is bounded. But SDI-QKD can be implemented in a oneway prepare-and-measure configuration without entanglement compared with DI-QKD. We propose a practical SDI-QKD protocol with four preparation states and three measurement bases by considering the maximal violation of dimension witnesses and specific processes of a QKD protocol. Moreover, we prove the security of the SDI-QKD protocol against collective attacks based on the min-entropy and dimension witnesses. We also show a comparison of the secret key rate between the SDI-QKD protocol and the standard QKD.     

Improvement of two-way continuous variable quantum cryptography by using additional noise

The performance of quantum key distribution such as one-way continuous variable protocols, can be increased by adding some noise on the reference side of error correction in the error-correction phase. For this reason, we here study this possibility in the case of two-way continuous variable system. Finally, the numerical results show that the using of additional noise gives two-way schemes better security performance in terms of secret key rates and resistance to channel excess noise.     

莱维噪声诱发的速度双模分布

研究了非线性阻尼驱动的惯性莱维飞行在自由势场中的反常输运。通过引入依赖于速度的非线性阻尼,长程跳跃的莱维粒子被束缚,粒子的动力学行为由发散收敛为与时间呈正比的正常扩散。观察到在自由势场中莱维飞行的速度的定态概率分布呈双模分布形式,更为重要的是,观察到双模形式与莱维系数及非线性阻尼系数相关。