分段均匀弦的Casimir能量

Casimir能量可看成是由于边界的出现、时空的弯曲以及某些背景场的存在而引起的量子场真空能量极化.由于对Casimir能量的研究能加深对量子场本质的了解,近来对它的研究兴趣正在增加.Brevik等人首先讨论了分段均匀弦的Casiwhr能量.但他们只讨论了闭玻色弦的Casimir能量.本文推广到开和闭的玻色弦,以及费米子弦情形.并且对超弦的Casimir能量也作了探讨.     

真空能量困扰着宇宙学

按照量子论,什么都没有的真空包含有能量.这种真空的“零点能”归根结底是来源于量子的不确定性.如果真空能量严格地为零,则不存在其能量的不确定性了.量子不确定性允许存在所谓虚光子,它不断地出现和消失从而赋予真空以能量. 按照相对论,这种零点能必然产生引力效应,从而影响宇宙的演化.最近,伯克利的P.Wesson提出这两种要求是不能调和的.按照他的说法,如果零点能真的存在,量子力学或宇宙学必须要作重大的修正. 零点能看来是真实的,因为它给出了可观测的效应,包括真空中两个金属板之间相互吸引的Casimir力和原子谱线的Lamb 移动等. 但是,…     

Casimer效应的一种严格计算方法

利用复变函数论中的Plana求和公式,我们计算了三维空间内真空电磁场零点起伏的Casimir能量,不引入任何截断参数或函数,而解出有限的解析表达式,与已知实验和理论符合.此外还讨论了在高维空间的和有质量标量场引起的Casimir效应.     

非平行导线型边界下Maxwell-Chern-Simons场的Casimir效应

在路径积分量子化框架下，利用复变函数论中的保角变换与Plana求和公式，计算了（2＋1）维空间中两个非平行导线型边界下Maxwell-Chern-Simons场的Casimir效应.不引入任何截断参数，而得出有限的解析表达式. 关键词： Casimir效应 路径积分 保角变换 Plana求和公式     

二维静态时空中Dirac场的重正化能动张量和Casimir效应

在一般渐近平直的二维静态黑洞时空中,利用重正化能动张量的一般性质, 对位于两“平行板”间满足Dirichlet条件的无质量Dirac场的重正化能动张量的真空期待值进行了分析和计算, 得到了一般表达式.利用该表达式可以给出各种具体渐近平直二维静态黑洞时空中的相应Casimir力.对于重正化能动张量及Casimir力与真空态定义(包括Boulware 真空态、Hartle-Hawking真空态和Unrum真空态三种情况)、Hawking辐射和反常迹的关系分别进行了讨论，给出了相应的表达式和计算结果. 关键词： 能动张量 Casimir 效应 黑洞 真空态     

量子真空与各向异性磁电材料之间的动量转移

各向同性材料内部量子真空涨落场具有各向同性，因此一般表现不出其宏观力学效应。但各向异性材料内部可以造就一个各向异性电磁环境，从而使得量子真空也具有各向异性秉性，表现为真空具有非零的动量与角动量密度，这导致各向异性材料与真空之间会发生宏观力学量（如动量、角动量甚至能量）的转移，表现出量子真空宏观力学效应。Feigel在近年研究过磁电材料中量子真空对材料的力学贡献（Phys Rev Lett，2004，92：020404），但只研究了最简单的本征模式（沿主轴传播）的真空水平动量对介质的贡献。我们用新的不同于Feigel的方法得到任意方向真空本征模式对各向异性材料的动量贡献，证明各向异性磁电材料因真空动量转移可以获得纳米每秒量级的速度，并指出该速度可以被最近才发展起来的光纤光学传感器所测量。     

量子环中极化子的温度效应

采用求解能量本征方程和LLP幺正变换方法,研究了量子环中极化子的温度效应.数值计算表明：当温度较低时,温度对极化子的基态能量无影响,当温度较高时,极化子的基态能量随温度的升高而增大;还表明极化子的基态能量随电子—声子耦合强度的增大而减小,随电子受限程度的增强（即量子环内径增大或外径减小）而增大,说明其量子尺寸效应非常显著.     

CdnOn（1≤n≤16）团簇光谱与电子性质的含时密度泛函理论研究

采用含时密度泛函理论对CdnOn（1≤n≤16）团簇的吸收光谱,能隙（HOMO-LUMO）及电子性质进行了模拟分析. 结果表明,当n≤3时,团簇的最低能量结构为平面结构,当4≤n≤16时,团簇的最低能量结构为三维笼状结构. 随着CdnOn（1≤n≤16）团簇尺寸的增大,团簇的吸收光谱逐渐红移,表现出较强的量子尺寸效应. 团簇CdnOn（3≤n≤15）的吸收峰主要集中在可见光区. 团簇的对称性越高,团簇的吸收峰越集中.     

含色散特异材料三明治结构的量子悬浮效应

在金属板与电介质材料板基底间插入色散特异材料板形成三明治结构,并对其Casimir作用力进行了研究.基于Casimir-Lifshitz理论,通过麦克斯韦应力张量计算了真空涨落的辐射压,并对三明治结构利用电磁模式传输矩阵方法进行了数值计算分析.计算结果表明,原本两板结构中存在的Casimir吸引力,在插入特异材料板后的三明治结构中将转变为斥力,从而使轻薄的金属板产生量子悬浮效应。讨论了特异材料板的色散电磁响应特性以及电介质板基底的影响,结果表明特异材料磁等离子频率越大、磁共振频率越小以及电介质板基底的介电常数越小时,三明治结构中获得的斥力越大.此外,板间距增加到一定范围时,三明治结构中将出现Casimir平衡回复力.特异材料填充因子越小、三明治结构中层距和层厚越大时,三明治结构间的回复力会出现在较长距的位置.三明治结构中的量子悬浮效应与平衡回复力可保证微纳米机械系统稳定性,展现出基于真空辐射压的应用前景.     

负折射率材料对产生Casimir排斥力的影响

研究了负折射率材料对产生Casimir排斥效应的影响. 两材料板间的Casimir排斥力的发生取决于两板以及其间媒质的电磁特性,通过理论与数值结果的分析研究给出电磁特性所影响排斥力的产生趋势. 对于由Drude-Lorentz型色散关系描述等效介电常数和磁导率的负折射率材料,调节各特征频率参数可实现Casimir排斥效应. 关键词： Casimir排斥力 负折射率材料 Drude-Lorentz型色散关系     

Attractive and repulsive Casimir vacuum energy with general boundary conditions

The infrared behaviour of quantum field theories confined in bounded domains is strongly dependent on the shape and structure of space boundaries. The most significant physical effect arises in the behaviour of the vacuum energy. The Casimir energy can be attractive or repulsive depending on the nature of the boundary. We calculate the vacuum energy for a massless scalar field confined between two homogeneous parallel plates with the most general type of boundary conditions depending on four parameters. The analysis provides a powerful method to identify which boundary conditions generate attractive or repulsive Casimir forces between the plates. In the interface between both regimes we find a very interesting family of boundary conditions which do not induce any type of Casimir force. We also show that the attractive regime holds far beyond identical boundary conditions for the two plates required by the Kenneth–Klich theorem and that the strongest attractive Casimir force appears for periodic boundary conditions whereas the strongest repulsive Casimir force corresponds to anti-periodic boundary conditions. Most of the analysed boundary conditions are new and some of them can be physically implemented with metamaterials.     

卡西米尔力

量子电动力学中的卡西米尔力是真空零点能的体现.广义的卡西米尔力则依赖于涨落介质的类型广泛地出现于物理中,包括量子,临界,戈德斯通模,以及非平衡卡西米尔力.长程关联的涨落介质和约束是产生卡西米尔力的两个条件.本文通过回顾卡西米尔物理的发展,讨论了不同类型的卡西米尔力,几种正规化方法,并对卡西米尔物理的进一步发展做了展望.     

On the Casimir effect without cutoff

The formulation of the Casimir effect without cutoffs is discussed. Our derivation emphasizes the decisive role of the free-space electromagnetic energy density. The zero point energy arises as an energy per unit volume, i.e., as local (in x space) energy density. It is given by the vaccum expectation value of the free-space Hamiltonian density in the Fock representation corresponding to the non-trivial geometry. The two Fock representations corresponding to the system with and without plates are proved to be inequivalent.     

Quantum Vacuum Fluctuations in a Chromomagnetic-Like Background

In this paper, we study the effects associated to quantum vacuum fluctuations of vectorial perturbations of the Abelian SU(2) Yang-Mills field in a static and homogeneous chromomagnetic-like background field, at zero temperature. We use periodic and antiperiodic boundary conditions in order to calculate the Casimir energy by means of the frequency sum technique and of the regularization method based on zeta functions, analyzing its behavior in the weak and strong coupling regimes. We compare the obtained results with the similar ones found for scalar and spinor fields placed in an ordinary magnetic field background. We show that only in the weak coupling regime the non-trivial topology of the system encoded in the antiperiodic boundary conditions changes the nature of the Casimir force with respect to the periodic ones. Considering the weak coupling scenario, we show that the introduction of a third polarization state in the perturbations makes manifest the effects on the Casimir energy due to the coupling with the chromomagnetic-like background field, for both the boundary conditions. Finally, in the strong coupling regime, in which the quantum vacuum is not stable due to the Nielsen-Olesen instabilities, we evaluate the effects of a compact extra dimension on its stabilization.     

Casimir Force of Squeezed Vacuum

The Casimir force of the quantized electromagnetic field in the squeezed vacuum state is calculated between a pair of parallel perfectly conducting plates at zero temperature.     

Casimir Force of Squeezed Vacuum

The Casimir force of the quantized electromagnetic field in the squeezed vacuum state is calculated betweena pair of parallel perfectly conducting plates at zero temperature.     

The Casimir interaction of a massive vector field between concentric spherical bodies

The Casimir interaction energy due to the vacuum fluctuations of a massive vector field between two perfectly conducting concentric spherical bodies is computed. The TE contribution to the Casimir interaction energy is a direct generalization of the massless case but the TM contribution is much more complicated. Each TM mode is a linear combination of a transverse mode which is the generalization of a TM mode in the massless case and a longitudinal mode that does not appear in the massless case. In contrast to the case of two parallel perfectly conducting plates, there are no TM discrete modes that vanish identically in the perfectly conducting spherical bodies. Numerical simulations show that the Casimir interaction force between the two bodies is always attractive.     

Casimir effect confronts cosmological constant

It has been speculated that the zero-point energy of the vacuum, regularized due to the existence of a suitable ultraviolet cut-off scale, could be the source of the non-vanishing cosmological constant that is driving the present acceleration of the universe. We show that the presence of such a cut-off can significantly alter the results for the Casimir force between parallel conducting plates and even lead to repulsive Casimir force when the plate separation is smaller than the cut-off scale length. Using the current experimental data we rule out the possibility that the observed cosmological constant arises from the zero-point energy which is made finite by a suitable cut-off. Any such cut-off which is consistent with the observed Casimir effect will lead to an energy density which is at least about 10¹² times larger than the observed one, if gravity couples to these modes. The implications are discussed.     

One-loop omega-potential of quantum fields with ellipsoid constant-energy surface dispersion law

Rapidly convergent expansions of a one-loop contribution to the partition function of quantum fields with ellipsoid constant-energy surface dispersion law are derived. The omega-potential is naturally decomposed into three parts: the quasiclassical contribution, the contribution from the branch cut of the dispersion law, and the oscillating part. The low- and high-temperature expansions of the quasiclassical part are obtained. An explicit expression and a relation of the contribution from the cut with the Casimir term and vacuum energy are established. The oscillating part is represented in the form of the Chowla–Selberg expansion of the Epstein zeta function. Various resummations of this expansion are considered. The general procedure developed is then applied to two models: massless particles in a box both at zero and nonzero chemical potential, and electrons in a thin metal film. Rapidly convergent expansions of the partition function and average particle number are obtained for these models. In particular, the oscillations of the chemical potential of conduction electrons in graphene and a thin metal film due to a variation of size of the crystal are described.