|
The security and recent technology of quantum key distribution
WANG Xiang-bin, PENG Cheng-zhi, YING Hao, PAN Jian-wei, MA Huai-xing, YANG Tao
Frontiers of Physics in China - Selected Publications from Chinese Universities. 2006, 1 (3): 251-255.
https://doi.org/10.1007/s11467-006-0023-y
In principle, quantum key distribution (QKD) can be used to make unconditionally secure private communication. However, the security of the existing real system for QKD needs to be carefully examined. Actually, the existing experiments based on weak coherent states are not secure under photon-number-splitting attack. Fortunately, the decoy-state method and the entanglement-distribution method can be used to realize the unconditionally secure QKD based on real-life systems with existing technology.
相关文章 |
多维度评价
|
|
Feedback control of quantum system
DONG Dao-yi, CHEN Zong-hai, ZHANG Chen-bin, CHEN Chun-lin
Frontiers of Physics in China - Selected Publications from Chinese Universities. 2006, 1 (3): 256-262.
https://doi.org/10.1007/s11467-006-0032-x
Feedback is a significant strategy for the control of quantum system. Information acquisition is the greatest difficulty in quantum feedback applications. After discussing several basic methods for information acquisition, we review three kinds of quantum feedback control strategies: quantum feedback control with measurement, coherent quantum feedback, and quantum feedback control based on cloning and recognition. The first feedback strategy can effectively acquire information, but it destroys the coherence in feedback loop. On the contrary, coherent quantum feedback does not destroy the coherence, but the capability of information acquisition is limited. However, the third feedback scheme gives a compromise between information acquisition and measurement disturbance.
相关文章 |
多维度评价
|
|
A new type of HTc superconducting film comb-shape resonator for radio frequency superconducting quantum interference devices
MAO Hai-yan, WANG Fu-ren, MENG Shu-chao, MAO Bo, LI Zhuang-zhi, NIE Rui-juan, LIU Xin-yuan, DAI Yuan-dong
Frontiers of Physics in China - Selected Publications from Chinese Universities. 2006, 1 (3): 301-304.
https://doi.org/10.1007/s11467-006-0018-8
A new type of HTc superconducting film comb-shape resonator for radio frequency superconducting quantum interference devices (RF SQUID) has been designed. This new type of superconducting film comb-shape resonator is formed by a foursquare microstrip line without a flux concentrator. The range of the center frequency of this type of resonator varies from 800 MHz to 1 300 MHz by changing the length of the teeth. In this paper, we report on simulating the relationship of the value of the center frequency and the length of the teeth, and testing the noise of HTc RF SQUID coupling this comb-shape resonator.
相关文章 |
多维度评价
|
|
Mechanism of field electron emission from carbon nanotubes
LI Zhi-bing, DENG Shao-zhi, XU Ning-sheng
Frontiers of Physics in China - Selected Publications from Chinese Universities. 2006, 1 (3): 305-316.
https://doi.org/10.1007/s11467-006-0029-5
Field electron emission (FE) is a quantum tunneling process in which electrons are injected from materials (usually metals) into a vacuum under the influence of an applied electric field. In order to obtain usable electron current, the conventional way is to increase the local field at the surface of an emitter. For a plane metal emitter with a typical work function of 5 eV, an applied field of over 1 000 V/μm is needed to obtain a significant current. The high working field (and/or the voltage between the electrodes) has been the bottleneck for many applications of the FE technique. Since the 1960s, enormous effort has been devoted to reduce the working macroscopic field (voltage). A widely adopted idea is to sharpen the emitters to get a large surface field enhancement. The materials of emitters should have good electronic conductivity, high melting points, good chemical inertness, and high mechanical stiffness. Carbon nanotubes (CNTs) are built with such needed properties. As a quasi-one-dimensional material, the CNT is expected to have a large surface field enhancement factor. The experiments have proved the excellent FE performance of CNTs. The turn-on field (the macroscopic field for obtaining a density of 10 μA/cm2 ) of CNT based emitters can be as low as 1 V/μm. However, this turn-on field is too good to be explained by conventional theory. There are other observations, such as the non-linear Fowler-Nordheim plot and multi -peaks field emission energy distribution spectra, indicating that the field enhancement is not the only story in the FE of CNTs. Since the discovery of CNTs, people have employed more serious quantum mechanical methods, including the electronic band theory, tight-binding theory, scattering theory and density function theory, to investigate FE of CNTs. A few theoretical models have been developed at the same time. The multi-walled carbon nanotubes (MWCNTs) should be assembled with a sharp metal needle of nano-scale radius, for which the FE mechanism is more or less clear. Although MWCNTs are more common in present FE applications, the single-walled carbon nanotubes (SWCNTs) are more interesting in the theoretical point of view since the SWCNTs have unique atomic structures and electronic properties. It would be very interesting if people can predict the behavior of the well-defined SWCNTs quantitatively (for MWCNTs, this is currently impossible). The FE as a tunneling process is sensitive to the apex-vacuum potential barrier of CNTs. On the other hand, the barrier could be significantly altered by the redistribution of excessive charges in the micrometer long SWCNTs, which have only one layer of carbon atoms. Therefore, the conventional theories based upon the hypothesis of fixed potential (work function) would not be valid in this quasi-one-dimensional system. In this review, we shall focus on the mechanism that would be responsible for the superior field emission characteristics of CNTs. We shall introduce a multi-scale simulation algorithm that deals with the entire carbon nanotube as well as the substrate as a whole. The simulation for (5, 5) capped SWCNTs with lengths in the order of micrometers is given as an example. The results show that the field dependence of the apex-vacuum electron potential barrier of a long carbon nanotube is a more pronounced effect, besides the local field enhancement phenomenon.
相关文章 |
多维度评价
|
|
Quantum oscillations in Pb/Si (111) heterostructure system
ZHANG Yan-feng, LI Shao-chun, MA Xu-cun, JIA Jin-feng, XUE Qi-kun
Frontiers of Physics in China - Selected Publications from Chinese Universities. 2006, 1 (3): 323-333.
https://doi.org/10.1007/s11467-006-0021-0
This paper summarizes our recent work on the study of quantum size effects (QSE) and novel physical properties of the Pb/Si (111) heterostructure. Two different types of samples were investigated. One is wedge-shaped Pb islands, and the other is atomically flat Pb thin films. With scanning tunneling microscopy (STM) manipulation, we observed an intriguing morphology dynamics of the islands that swings between two extreme energy states, like that in a classical pendulum. We show that the dynamics is a result of the competition between the QSE and the classical step free energy minimizing effect. For the second type of the samples, the QSE is studied in terms of thickness-dependent film stability, electronic structure and physical properties by using STM, angle-resolved photoemission spectroscopy (ARPES) and transport measurement. The results consistently reveal the formation of quantum well states (QWS) due to electron confinement in the films. This size effect could greatly modify the electronic structure near the Fermi level and lead to quantum oscillations in superconductivity, electron-phonon coupling and thermal expansion. The work unambiguously demonstrates the possibility of quantum engineering of physical properties of thin films by exploiting well-controlled and thickness-dependent QSE.
相关文章 |
多维度评价
|
|
Characteristics and developments of quantum-dot infrared photodetectors
ZHANG Guan-jie, SHU Yong-chun, YAO Jiang-hong, SHU Qiang, DENG Hao-liang, JIA Guo-zhi, WANG Zhan-guo
Frontiers of Physics in China - Selected Publications from Chinese Universities. 2006, 1 (3): 334-338.
https://doi.org/10.1007/s11467-006-0030-z
Quantum dots infrared photodetectors (QDIPs) theoretically have several advantages compared with quantum wells infrared photodetectors (QWIPs). In this paper, we discuss the theoretical advantages of QDIPs including the normal incidence response, lower dark current, higher responsivity and detectivity, etc. Recent device fabrication and experiment results in this field are also presented. Based on the analysis of existing problems, some approaches that would improve the capability of the device are pointed out.
相关文章 |
多维度评价
|
|
Thermodynamic properties of noble metal clusters: molecular dynamics simulation
WU Zhi-min, WU Zhi-min, WANG Xin-qiang, WANG Xin-qiang, XIAO Xu-yang, XIAO Xu-yang, HE Huan-dian, HE Huan-dian, LUO Qiang, LUO Qiang
Frontiers of Physics in China - Selected Publications from Chinese Universities. 2006, 1 (3): 351-356.
https://doi.org/10.1007/s11467-006-0034-8
The thermodynamics properties of noble metal clusters AuN, AgN, CuN, and PtN (N = 80, 106, 140, 180, 216, 256, 312, 360, 408, 500, 628, 736, and 864) are simulated by micro-canonical molecular dynamics simulation technique. The potential energy and heat capacities change with temperature are obtained. The results reveal that the phase transition temperature of big noble metal clusters (N "e312 for Au, 180 for Ag and Cu, and 360 for Pt) increases linearly with the atom number slowly and approaches gently to bulk crystals. This phenomenon indicates that clusters are intermediate between single atoms and molecules and bulk crystals. But for the small noble clusters, the phase transition temperature changes irregularly with the atom number due to surface effect. All noble metal clusters have negative heat capacity around the solid-liquid phase transition temperature, and hysteresis in the melting / freezing circle is derived in noble metal clusters.
相关文章 |
多维度评价
|
|
Influence of the rare earth element substitution on oxygen adsorption-desorption properties of YBCO
FAN Yu-shan, SONG Hong-zhang, LI Zhi-hui, YANG De-lin, HU Xing
Frontiers of Physics in China - Selected Publications from Chinese Universities. 2006, 1 (3): 368-370.
https://doi.org/10.1007/s11467-006-0031-y
The oxygen adsorption-desorption properties of RBa2Cu3O7-δ R = Gd, Er, Eu, Dy, Sm, Ho and Nd?nd Y1-χLaχBa2Cu3O7-δ (χ = 0.1, 0.5 and 1.0) were investigated from room temperature to 950 oC by thermogravimetry (TG). The results show that all samples will release oxygen with the increasing of temperature and the released oxygen can be absorbed back into the sample when temperature decreases. However, dependent on the rare earth element, the amount of the released oxygen is different for these samples. Moreover, in the temperature increasing and decreasing circle the repetition of oxygen adsorption-desorption is also different.
相关文章 |
多维度评价
|
19篇文章
|