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Quantum secure direct communication and deterministic secure quantum communication
LONG Gui-lu, DENG Fu-guo, WANG Chuan, WEN Kai, WANG Wan-ying, LI Xi-han
Front. Phys. . 2007, 2 (3): 251-272.
https://doi.org/10.1007/s11467-007-0050-3
In this review article, we review the recent development of quantum secure direct communication (QSDC) and deterministic secure quantum communication (DSQC) which both are used to transmit secret message, including the criteria for QSDC, some interesting QSDC protocols, the DSQC protocols and QSDC network, etc. The difference between these two branches of quantum communication is that DSQC requires the two parties exchange at least one bit of classical information for reading out the message in each qubit, and QSDC does not. They are attractive because they are deterministic, in particular, the QSDC protocol is fully quantum mechanical. With sophisticated quantum technology in the future, the QSDC may become more and more popular. For ensuring the safety of QSDC with single photons and quantum information sharing of single qubit in a noisy channel, a quantum privacy amplification protocol has been proposed. It involves very simple CHC operations and reduces the information leakage to a negligible small level. Moreover, with the one-party quantum error correction, a reation has been established between classical linear codes and quantum one-party codes, hence it is convenient to transfer many good classical error correction codes to the quantum world. The one-party quantum error correction codes are especially designed for quantum dense coding and related QSDC protocols based on dense coding.
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An alternative quantum theory for single particles and a proposed experimental test
LIU Quan-hui
Front. Phys. . 2007, 2 (3): 273-278.
https://doi.org/10.1007/s11467-007-0040-5
An alternative quantum theory for single particles bounded in the external field proposed in 1986 (Huang X. Y., Phys. Lett. A., 1986, 115: 310) is further developed from which the energy of the state for the single particle takes one of the eigenvalues of the quantum Hamiltonian, and the usual quantum mechanics for the particle in a stationary state holds only in the statistical sense. In light of the theory, the particle of definite energy, ground-state-energy for instance, can exhibit a novel periodic behavior. This result for the ground-state-energy state neutron in the Earth's gravitational field is experimentally testable using ultracold neutron beam passing through the same apparatus that was devised in 2002 to identify the energy quantization of neutron in the field (Nesvizhevsky V. V., et al., Nature, 2002, 415: 297).
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Size dependence of phase transition temperatures of ferromagnetic, ferroelectric and superconductive nanocrystals
LANG Xing-you, JIANG Qing
Front. Phys. . 2007, 2 (3): 289-311.
https://doi.org/10.1007/s11467-007-0049-9
With the miniaturization of devices, size and interface effects become increasingly important for the properties and performances of nanomaterials. Here, we present a thermodynamic approach to the mechanism behind size-induced unusual behavior in the phase stabilities of ferromagnetic (FM), antiferromagnetic (AFM), ferroelectric (FE), and superconductive (SC) nanocrystals, which are different dramatically from their bulk counterparts. This method is based on the Lindemann criterion for melting, Mott s expression for the vibrational melting entropy, and the Shi model for the size-dependent melting temperature. Simple and unified functions, without any adjustable parameter, are established for the size and interface dependences of thermal and phase stabilities of FM, AFM, FE and SC nanocrystals. According to these analytic functions, as the size of nanocrystals is reduced, the thermal and phase stabilities may strengthen or weaken, depending on the confluence of the surface/volume ratio of nanocrystals and the FM(AFM, FE or SC)/substrate interface situations. The validity of this model is confirmed by a large number of experimental results. This theory will be significant for the choice of materials and the design of devices for practical application.
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Influence of the stress on magnetoelectric effect in magnetostrictive-PZT bilayers
DING Jian-ming, JIANG Qing, ZHONG Chong-gui
Front. Phys. . 2007, 2 (3): 312-317.
https://doi.org/10.1007/s11467-007-0041-4
In this letter, we investigate the influence of the stress on magnetoelectric (ME) effect in a magnetostrictive-PZT bilayer. ME voltage coefficient α*E =δEδH?????, where δE is the induced electric field for an applied alternating current (ac) magnetic field δH, is obtained by solving the stress-related piezoelectric constitutive equation and the conventional magnetostrictive equation with appropriate boundary condition. Based on the free-energy density function of the PZT film in stress state, we get the stress-related piezoelectric charge coefficient pd*31 and dielectric permittivity pε*33. After taking the cobalt ferrite (CFO) as magnetostrictive phase, it is found that α*E increases with decreasing 2-d compressive stress for CFO-PZT, which not only is qualitatively consistent with previous experimental measurements, but also provides a possible route to improve the ME effect.
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Solitary wave solutions of nonlinear financial markets: data-modeling-concept-practicing
MA Jin-long, MA Fei-te
Front. Phys. . 2007, 2 (3): 368-374.
https://doi.org/10.1007/s11467-007-0047-y
This paper seeks to solve the difficult nonlinear problem in financial markets on the complex system theory and the nonlinear dynamics principle, with the data-model-concept-practice issue-oriented reconstruction of the phase space by the high frequency trade data. In theory, we have achieved the differentiable manifold geometry configuration, discovered the Yang-Mills functional in financial markets, obtained a meaningful conserved quantity through corresponding space-time non-Abel localization gauge symmetry transformation, and derived the financial solitons, which shows that there is a strict symmetry between manifold fiber bundle and gauge field in financial markets. In practical applications of financial markets, we have repeatedly carried out experimental tests in a fluctuant evolvement, directly simulating and validating the existence of solitons by researching the price fluctuations (society phenomena) using the same methods and criterion as in natural science and in actual trade to test the stock Guangzhou Proprietary and the futures Fuel Oil in China. The results demonstrate that the financial solitons discovered indicates that there is a kind of new substance and form of energy existing in financial trade markets, which likely indicates a new science paradigm in the economy and society domains beyond physics.
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11 articles
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