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1.
存在内禀退相干时二项式光场中原子的布居数反转 总被引:1,自引:1,他引:0
在Milburn内禀退相干模型下,研究了二项式光场与二能级原子相互作用系统中原子的布居数反转,分析了内禀退相干,二项式光场系数和场的最大光子数对原子布居数反转的影响.结果表明,存在内禀退相干时,原子布居数反转出现明显的崩塌-回复现象,随着时间的演化,Rabi振荡的包络值将很快的崩塌到零,并且随着内禀退相干因子的减小,衰减加剧;当内禀退相干因子不变时,二项式光场从相干态过渡到中间态,以及由中间态到数态过程中,原子布居数反转出现明显的崩塌-回复现象,而且Rabi振荡的频率会明显加快;当二项式光场的最大光子数增大时,原子布居差的崩塌-回复现象就会逐渐消失. 相似文献
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时空度规是广义相对论的一个基础性概念,是宇宙学和天体物理学建立模型的逻辑基础.将随时序参数变化的空间尺度 因子函数引入相对论四维时空间隔模型,研究空间球对称形式的四维平直时 空度规、Schwarzschild度规、Robertson-Walker (R-W)度规之间的变换条件.基于空间变尺度因子球坐标系的时空间隔, 通过严格的计算,推导出R-W度规中与k=±1对应的尺度因子函数解析解,还推导出星球外非真空条件下的四维时空度规. 提出了一种理解现代物理学非平直时空模型的新视角. 相似文献
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基于分子两体势,用Monte Carlo方法计算向列相液晶微滴.两体势基于格点模型,是空间各向异性的且依赖于液晶的弹性常数.假定向列相液晶微滴具有自由表面,引入切向内禀强度定量描写表面引发的分子内禀易取向的强弱.通过各向异性势的两种方案,在低温下计算切向内禀强度和二阶序参数在微滴内不同区域的变化,与Lebwohl-Lasher模型作对比分析.结果表明:只有一种方案在微滴表面产生内禀易取向,且内禀强度值的大小与K33/K11值有关;空间不完整的向列相液晶使得微滴由内层到外层有序度越来越低. 相似文献
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基于Gruhn-Hess两体势修正模型,用Monte Carlo方法模拟向列相液晶微滴.Gruhn-Hess两体势是空间各向异性的,修正模型的势参数依赖于液晶的弹性常数K11、K22、K33及表面弹性常数K13.假设向列相液晶微滴具有自由表面,在低温下计算分子二阶序参数和切向内禀强度在微滴内不同区域的变化,并与Gruhn-Hess两体势模型一作对比分析.结果表明:附加K13项的修正模型在微滴表面产生内禀锚定,其大小决定了内禀易取向方向及内禀锚定强度的大小,且内禀强度的大小与K33/K11值有关;空间不完整的向列相液晶微滴由内层到外层有序度逐渐降低. 相似文献
5.
普通晶体破缺了空间平移对称性,而时间晶体则破缺了时间平移对称性。探索四维时空中晶体行为是一个崭新的研究方向,将会带来创新性的凝聚态器件和应用。在计算机芯片或是超导器件的内部,无数的电子在排列成晶格的离子间穿梭而过。这样的景象会不会在时间而不是空间中周而复始呢?传统的凝聚态器件或是电子元件会不会有四维时空中的新奇应用呢? 相似文献
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交换超算符方法的李代数研究 总被引:1,自引:1,他引:0
本文讨论了交换超算符方法的理论基础,结果表明由交换超算符所定义的算符集合g是一个李代数,交换超算符的定义就是李代数中内导子的定义,由此得出一些交换超算符间的代数关系。证明了g中所有算符诱导的超算符集合也是一个李代数,指出了与g对应的是由复盖群派生的,有内积定义的李群,而角动量超算符是由矢量场的内禀角动量和单位算符的直积所生成。结论是交换超算符方法的理论基础是李代数。 相似文献
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《量子光学学报》2018,(4)
Dicke模型(DM)用于描述单模玻色光场与多个全同二能级原子相互作用。本文利用自旋相干态变分法得到两模光机械系统中基态能量的精确解,并通过变分法求得相变点并画出基态相图,并在此基础上研究原子-场耦合强度等系统参数对基态稳定性的影响。通过稳定性讨论,我们发现:原子-光子耦合常数g和光子-声子耦合常量ζ都会对光机械系统的基态特性产生影响。当双模光腔变成单模光腔时,机械振子能诱导超辐射相的塌缩;而且当光子-声子耦合强度大时,超辐射相被完全压制,而直接出现两原子能级之间的转移;存在不稳定的非零光子态,类似于超辐射态。光机械腔中光子-声子耦合诱导的超辐射态的塌缩和复苏是不同于光腔内囚禁的BEC系统,即机械振子不存在时的情况,而双模光腔对量子相变点和相图预期也会有影响。可见,分析机械振子的对多稳性和相关的量子相变的影响是非常有意义的课题。 相似文献
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The null-surface formulation of general relativity (NSF) describes gravity by using families of null surfaces instead of a spacetime metric. Despite the fact that the NSF is (to within a conformal factor) equivalent to general relativity, the equations of the NSF are exceptionally difficult to solve, even in 2+1 dimensions. The present paper gives the first exact \((2+1)\)-dimensional solution that depends nontrivially upon all three of the NSF’s intrinsic spacetime variables. The metric derived from this solution is shown to represent a spacetime whose source is a massless scalar field that satisfies the general relativistic wave equation and the Einstein equations with minimal coupling. The spacetime is identified as one of a family of \((2+1)\)-dimensional general relativistic spacetimes discovered by Cavaglià. 相似文献
12.
S. Brian Edgar 《International Journal of Theoretical Physics》1993,32(1):121-135
It has recently been asked whether a fourth-order tensorK with all the algebraic symmetries of a Riemann tensor, and which satisfies the Ricci equations (with covariant derivative constructed from the metricg in the usual way), is always equal to the Riemann tensorR of the metricg; and a positive answer has been given for a generic tensorK in any nonflat 4-dimensional spacetime. In this paper it is shown that the result is also true in a generic 4-dimensional spacetime for any nontrivial tensorK. In addition, those special spacetimes where the result fails are given explicitly in terms of the Petrov types of their Weyl and Plebanski tensors. 相似文献
13.
We consider the operator product expansion for quantum field theories on general analytic 4-dimensional curved spacetimes within an axiomatic framework. We prove under certain general, model-independent assumptions that such an expansion necessarily has to be invariant under a simultaneous reversal of parity, time, and charge (PCT) in the following sense: The coefficients in the expansion of a product of fields on a curved spacetime with a given choice of time and space orientation are equal (modulo complex conjugation) to the coefficients for the product of the corresponding charge conjugate fields on the spacetime with the opposite time and space orientation. We propose that this result should be viewed as a replacement of the usual PCT theorem in Minkowski spacetime, at least in as far as the algebraic structure of the quantum fields at short distances is concerned. 相似文献
14.
G.F. Chapline 《Physics letters. [Part B]》1980,94(3):394-396
By way of a simple example it is shown that if a broken symmetry solution of the Yang-Mills equations in a higher-dimensional flat spacetime is assumed to vary only in a curved four-dimensional spacetime subspace, one is led naturally to the Einstein action. 相似文献
15.
Hao Liao Changli Wei Songbai Chen 《International Journal of Theoretical Physics》2018,57(10):2949-2955
In this paper, we have investigated the absorption probability and Hawking radiation of electromagnetic field while it coupling with Einstein tensor in the background of 4-dimensional Reissner-Nordström(RN) black hole spacetime. Our results indicate that the properties of the absorption probability and Hawking radiation depend not only on the coupling parameter, but also on the parity of the electromagnetic field, which is quite different from those of the usual electromagnetic field without coupling in the 4-dimensional spacetime.The absorption probability, power emission spectra and luminosity of Hawking radiation decreases with the increase of coupling parameter α when the coupled electromagnetic field have odd-parity, and increases with the increase of coupling parameter α when the coupled electromagnetic field have even-parity. 相似文献
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The most general time-independent spherically symmetric (in the usual three space dimensions) solution to the five-dimensional vacuum Einstein equations is found, subject to the existence of a Killing vector in the fifth direction. The significance of these solutions is discussed within the context of a previously proposed extension of the Kaluza-Klein model in which the universe, although (4+1)-dimensional, has evolved over cosmic times into an effectively (3+l)-dimensional one. 相似文献
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This paper investigates the quantum Dirac field in n+1-dimensional flat
spacetime and derives a lower bound in the form of quantum
inequality on the energy density averaged
against spacetime sampling functions. The state-independent quantum inequality
derived in the present paper is
similar to the temporal quantum energy inequality and
it is stronger for massive
field than for massless one. It also
presents the concrete results of the quantum inequality in 2 and
4-dimensional spacetimes. 相似文献
18.
We consider a non-diagonal cylindrically symmetric metric in the Kaluza-Klein spacetime. We obtain a number of homogeneous and inhomogeneous perfect fluid cosmological models, which include the 5-dimensional analogue of the recently found 4-dimensional non-singular stiff fluid model. Amongst the homogeneous models, which are all as expected big-bang singular, there is the 5-dimensional version of the Friedman-Robertson-Walker flat model. 相似文献
19.
J. G. Williams 《General Relativity and Gravitation》1991,23(2):181-187
A solution is presented for a rotating perfect fluid in (2+1)-dimensional spacetime. A complete metrical kink is seen to be present, provided that the boundary conditions are correctly formulated. 相似文献
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A suitably chosen complex parametrization of the 3-sphere is used to construct a (3 + 1)-dimensional spacetime that is homogeneous and satisfies the various standard energy conditions. The spacetime has nonzero vorticity, closed timelike curves and is shown to possess a Finkelstein-Misner kink. Hopf projection from the 3-sphere to a 2-sphere reduces the model to a previously known toy model in lower dimensions. 相似文献