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[en] A quantum representation model for multiple images is firstly proposed, which could save more storage space than the existing quantum image representation models and allow quantum hardware to encrypt an arbitrary number of images simultaneously. Moreover, the definition and the quantum circuit of quantum 3D Arnold transform are given based on the proposed quantum representation model for multiple images. Furthermore, a novel quantum multi-image encryption scheme is devised by combining quantum 3D Arnold transform and quantum XOR operations with scaled Zhongtang chaotic system. Theoretically, the proposed quantum image encryption scheme could encrypt many images simultaneously. Numerical simulations and theoretical analyses demonstrate that the proposed quantum multi-image encryption scheme outperforms both its classical counterparts and the existing typical quantum image encryption algorithms in terms of security, robustness, encryption capacity and computational complexity.
[en] Measurement-device-independent quantum key distribution (MDI-QKD) is a promising protocol for realizing long-distance secret keys sharing. However, its key rate is relatively low when the finite-size effect is taken into account. In this paper, we consider statistical fluctuation analysis for the three-intensity decoy-state MDI-QKD system based on the recent work (Zhang et al. in Phys Rev A 95:012333, 2017) and further compare its performance with that of applying the Gaussian approximation technique and the Chernoff bound method. The numerical simulations demonstrate that the new method has apparent enhancement both in key generation rate and transmission distance than using Chernoff bound method. Meanwhile, the present work still shows much higher security than Gaussian approximation analysis.
[en] Coherence, detectability and correlation in a quantum measurement process are studied by means of the generalized Coleman–Hepp model, in which a spin of a propagating particle is measured and a detector system consists of a one-dimensional array of independent spin-1/2 particles. It is found that the coherence of the measured particle decreases in time, while the detectability of the particle spin by the whole detector system increases. The coherence and detectability satisfy a trade-off relation. The correlation between the particle spin and the whole detector system grows in time and its dependence on the interaction strength is clarified. On the other hand, after the correlation between the particle spin and the individual detector particle is created by the interaction, it decays in time due to the interaction with another detector particle. It is shown that the strong particle–detector interaction not only creates large correlation but also causes the rapid decay of the correlation. In the asymptotic limit, the entanglement between the particle spin and the individual detector particle becomes zero, while the quantum discord can take finite values. Furthermore, a numerical calculation reveals that the optimum measurement for detecting the particle spin is equal to that quantifying the classical correlation and the quantum discord.
[en] We present an explicit family of two-qubit X states with entanglement-preserving unitary equivalence to the set of general states; that is, for any spectrum–entanglement combination achievable by general states, this family contains an X state of the same spectrum and entanglement.
[en] Quantum digital signature offers an information theoretically secure way to guarantee the identity of the sender and the integrity of classical messages between one sender and many recipients. The existing unconditionally secure protocols only deal with the problem of sending single-bit messages. In this paper, we modify the model of quantum digital signature protocol and construct an unconditionally secure quantum digital signature protocol which can sign multi-bit messages at one time. Our protocol is against existing quantum attacks. Compared with the previous protocols, our protocol requires less quantum memory and becomes much more efficient. Our construction makes it possible to have a quantum signature in actual application.
[en] We consider two qubits prepared in a product state and evolved under the magnetic dipolar interaction (MDI). We describe the dependence of the entanglement generated by the MDI with time, with the interaction parameters, and with the system’s initial state, identifying the symmetry and coherence aspects of those initial configurations that yield the maximal entanglement. We also show how one can obtain maximum entanglement from the MDI applied to some families of partially entangled initial states.
[en] Two modified measurement-device-independent quantum key distribution protocols based on the decoherence-free subspace are presented in this study. The proposed protocols are tolerant of the fault with collective-rotation noise and collective-dephasing noise. Exploiting the logical qubits comprised by two pairs of entanglement photons in decoherence-free subspace states, the mutually unbiased bases are formed by introducing the spatial degrees of freedom which reduces the experiment difficulty. There are only Bell-state preparation and collective Bell-state measurement needed in our protocols. Moreover, a brief discussion on the security of the proposal in the communication process is given.
[en] We discuss the reversible storage of an entangled two-mode wavepacket in separated two atomic ensembles based on electromagnetically induced transparency. By introducing wavepacket dark-states, we show the dynamic transfer of quantum information of the wavepacket between the optical field and the atomic ensembles. We examine in detail the performance of the scheme focusing on the reversible storage of an entangled two-photon wavepacket in the case where the effects of the environment and the thermal motions of atoms are taken into consideration.
[en] A master equation has been constructed for a global system–bath interaction in the both absence and presence of non-Markovian noise. For the memoryless case, it has been exactly solved for a paradigmatic class of two qubit states in high- and zero-temperature thermal environment. For the non-Markovian model, it has been solved for zero-temperature bath. The evolution of quantum coherence and entanglement has been observed in the presence of the above-mentioned interactions. We show that the global part of the system–bath interaction compensates for the decoherence, resulting in slowdown of coherence and entanglement decay. For an appropriately defined limiting case, both coherence and entanglement show freezing behavior for the high-temperature bath. In case of zero-temperature bath, the mentioned interaction not only stabilizes the non-classical correlations, but also enhances them for a finite period. For the memory-dependent case, we have seen that the global interaction enhances the backflow of information from environment to the system, as it enhances the regeneration of coherence and entanglement. Also we have studied the generation of quantum Fisher information by the mentioned process. An intuitive measure of non-classicality based on non-commutativity of quantum states has been considered. Bounds on generated quantum Fisher information have been found in terms of quantumness and coherence. This gives us a novel understanding of quantum Fisher information as a measure of non-classicality.