共查询到13条相似文献,搜索用时 46 毫秒
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超光速研究的40年——回顾与展望 总被引:1,自引:0,他引:1
自美国物理学家O.M.Bilanuik和E.C.Sudarshan(1962年)以及G.Feinberg(1967年)的开创性工作以来,在美国、欧洲和中国都对超光速展开了研究。根据A.Einstein于1905年发表的原始论文,超光速没有存在的可能,但其1907年的论文对“信号传播不能超光速”却不很肯定。文章把速度问题分解为若干类、项,并提出“广义信息速度”定义以利于对众多速度概念的讨论。在反思了40年来(1962—2003年)的超光速研究以后,得出结论认为“超过真空中光速c”是一种可实现的科学陈述。 相似文献
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宇宙早期的强子时期,光速比c大,实际上可达v=75c。故光速随时间缓慢减小,从v降低到今天的值(c)。另一方面,根据对128个类星体吸收线的测量,在过去的6~12Ga期间,精细结构常数α平均增大了6×10-6,科学家们认为可能是光速变化造成的。对上述效应进行研究以了解宇宙的过去是有趣的。还深入讨论了超光速研究中的一些问题———微观粒子速度的定义,引力速度,量子纠缠态作用速度以及超距作用。对这些概念有了更准确的理解。 相似文献
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利用人工源超低频电磁波监测地震的试验与分析 总被引:26,自引:0,他引:26
由人工产生大功率超低频(SLF)电磁波可以在地面很大范围的许多测点同时测量该信号,利用它可以研究地下电阻率结构和空间电磁场;研究地震等引起的电磁场异常变化;探测地壳结构和地下资源,具有广阔的应用前景和发展潜力。在北京等地区的观测表明,SLF信号的功率谱密度超过天然场源信号数倍以上,所得到的视电阻率数据精度远高于天然源方法,并有长时间的稳定性。在试验测量期间距测点约120 km发生的迁安4.2级地震与观测的电磁场异常和视电阻率的变化有较好的对应性,对产生这些变化的可能的成因机制进行了分析和探讨。 相似文献
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Martin Ligare 《Journal of Modern Optics》2013,60(17):1551-1559
Dielectric materials in which both the relative permittivity, ε, and the relative permeability, μ, are negative exhibit striking optical properties, which are a consequence of the fact that the effective index of refraction in such materials is negative. Most studies of the propagation of electromagnetic fields in these media have concentrated on classical fields with well-defined phases. In contrast, I use simple fully-quantized models to illustrate how some of the striking properties of negative-index media are manifested in the propagation of single, spontaneously emitted, photons. Single-photon quantum fields do not have an absolute phase, but the examples in this paper demonstrate a quantum analog of the negative phase accumulated by classical fields as photons propagate through negative-index media. The single photons also exhibit classical reflection and transmission coefficients, as well as the expected group velocity. 相似文献
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波粒二象性理论的若干问题 总被引:7,自引:2,他引:5
论述了光波和物质波的波粒二象性理论的发展,讨论了该理论的存留问题。认为光子的静质量和光子的内部结构仍是科学中的关键性疑点。指出,虽然波粒二象性成立的前提是波长足够小,但在现有理论中却提不出一条清晰的界线。讨论了光波和电磁波是物质还是物质属性的问题。提出了对de Broglie波超光速相速的疑问。分析表明,如何建立电磁脉冲的粒子形象的问题仍需解决。此外,探讨了当电磁脉冲以超光速传播时相对论是否受破坏。最后,讨论了消失波的粒子性和虚光子问题。 相似文献
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论狭义相对论的理论发展和实验检验 总被引:14,自引:2,他引:12
狭义相对论(SR)可概括为10个主要方面,即1个变换,2个公设,3个公式,4个推论。目前对狭义相对论的质疑集中在“光速不变公设”和“光速不能超过推论”这两方面。1992年以后的10年间已做成了若干超光速实验,有的在经典领域,有的在量子领域。2001年,有迹象表明在大的宇宙时间尺度上光速缓慢减小,这引起了对光速是否真的恒定不变的质疑,SR似已受到挑战。国际科学界如使新理论成立,将是Einstein提出SR以来的一次科学革命。 相似文献
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We have studied theoretically the dispersion of ultrafast coherent pulses in GaAs/AlGaAs quantum well waveguide structures as a function of optical intensity. Semiconductor Bloch equations are used to obtain the polarization induced in the medium due to an incident Gaussian electromagnetic beam. The partial differential equation describing the pulse propagation in the presence of group velocity dispersion is used to analyze the role of higher-order dispersion on femtosecond pulse propagation in the waveguide. Due consideration has been given to the intensity dependent optical susceptibility of the medium. The results of the numerical analysis manifest significant influence of higher-order dispersion on femtosecond pulse propagation over short waveguide distance. 相似文献
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Martin W. McCall 《Journal of Modern Optics》2013,60(16):1727-1740
We review various published definitions associated with the phenomenon of negative phase velocity propagation of electromagnetic waves in meta-media, as observed through negative refraction. For the principal definition, based on the Poynting vector and the wave vector having negative scalar product, we summarise the various material constraints that have been derived. The distinction between criteria based on the Poynting vector and the group velocity are considered, both in respect of causality, and in the context of moving media. Instances where a fully covariant definition is necessary are also identified, and compared with other results from the extant literature. Satisfaction of the NPV propagation criterion is also considered for surface plasmons. 相似文献
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In periodic optical media, the group velocity is defined as the gradient with respect to wave-vector of the corresponding Bloch mode frequency dispersion curve, forming the photonic band structure. Instead of deducing it from the numerically computed photonic crystal band structure, the group velocity can be calculated directly from the integral of the Poynting vector over the crystal unit cell, the physical meaning of which is immediately perceivable. The related formula, which can be regarded as the application of Hellmann–Feynman theorem to electromagnetism, has been reported previously though without proof. We provide hereafter a full derivation of that formula starting from Maxwell’s equations and we discuss its usefulness in photonics. 相似文献
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Qile Li Iolanda Di Bernardo Johnathon Maniatis Daniel McEwen Amelia Dominguez-Celorrio Mohammad T. H. Bhuiyan Mengting Zhao Anton Tadich Liam Watson Benjamin Lowe Thi-Hai-Yen Vu Chi Xuan Trang Jinwoong Hwang Sung-Kwan Mo Michael S. Fuhrer Mark T. Edmonds 《Advanced materials (Deerfield Beach, Fla.)》2024,36(24):2312004
Quantum anomalous Hall (QAH) insulators transport charge without resistance along topologically protected chiral 1D edge states. Yet, in magnetic topological insulators to date, topological protection is far from robust, with zero-magnetic field QAH effect only realized at temperatures an order of magnitude below the Néel temperature TN, though small magnetic fields can stabilize QAH effect. Understanding why topological protection breaks down is therefore essential to realizing QAH effect at higher temperatures. Here a scanning tunneling microscope is used to directly map the size of exchange gap (Eg,ex) and its spatial fluctuation in the QAH insulator 5-layer MnBi2Te4. Long-range fluctuations of Eg,ex are observed, with values ranging between 0 (gapless) and 70 meV, appearing to be uncorrelated to individual surface point defects. The breakdown of topological protection is directly imaged, showing that the gapless edge state, the hallmark signature of a QAH insulator, hybridizes with extended gapless regions in the bulk. Finally, it is unambiguously demonstrated that the gapless regions originate from magnetic disorder, by demonstrating that a small magnetic field restores Eg,ex in these regions, explaining the recovery of topological protection in magnetic fields. The results indicate that overcoming magnetic disorder is the key to exploiting the unique properties of QAH insulators. 相似文献