Persistent narrowing of nuclear-spin fluctuations in InAs quantum dots using laser excitation

We demonstrate the suppression of nuclear-spin fluctuations in an InAs quantum dot and measure the timescales of the spin narrowing effect. By initializing for tens of milliseconds with two continuous wave diode lasers, fluctuations of the nuclear spins are suppressed via the hole-assisted dynamic nuclear polarization feedback mechanism. The fluctuation narrowed state persists in the dark (absent light illumination) for well over 1 s even in the presence of a varying electron charge and spin polarization. Enhancement of the electron spin coherence time (T2*) is directly measured using coherent dark state spectroscopy. By separating the calming of the nuclear spins in time from the spin qubit operations, this method is much simpler than the spin echo coherence recovery or dynamic decoupling schemes.     

Soliton molecules and the CRE method in the extended mKdV equation

The soliton molecules of the(1+1)-dimensional extended modified Korteweg–de Vries(mKdV)system are obtained by a new resonance condition, which is called velocity resonance. One soliton molecule and interaction between a soliton molecule and one-soliton are displayed by selecting suitable parameters. The soliton molecules including the bright and bright soliton, the dark and bright soliton, and the dark and dark soliton are exhibited in figures 1–3, respectively.Meanwhile, the nonlocal symmetry of the extended mKdV equation is derived by the truncated Painlevé method. The consistent Riccati expansion(CRE) method is applied to the extended mKdV equation. It demonstrates that the extended mKdV equation is a CRE solvable system. A nonauto-B?cklund theorem and interaction between one-soliton and cnoidal waves are generated by the CRE method.     

The accretion of dark energy onto a black hole

The stationary, spherically symmetric accretion of dark energy onto a Schwarzschild black hole is considered in terms of relativistic hydrodynamics. The approximation of an ideal fluid is used to model the dark energy. General expressions are derived for the accretion rate of an ideal fluid with an arbitrary equation of state p = p(ρ) onto a black hole. The black hole mass was found to decrease for the accretion of phantom energy. The accretion process is studied in detail for two dark energy models that admit an analytical solution: a model with a linear equation of state, p = α(ρ ? ρ₀), and a Chaplygin gas. For one of the special cases of a linear equation of state, an analytical expression is derived for the accretion rate of dark energy onto a moving and rotating black hole. The masses of all black holes are shown to approach zero in cosmological models with phantom energy in which the Big Rip scenario is realized.     

四能级系统中ac-Stark分裂研究

提出一双光场作用下的四能级系统,并对四能级模型的共振荧光谱作了详尽的研究.原子的共振荧光谱随Rabi频率的变化展示出能级的acStark分裂,且在很大参量范围内光谱具有这一特性.但当只有一个激发通道时不产生acStark分裂.在一定的条件下原子的共振荧光谱出现了两条黑线(darkline).可以认为acStark分裂的产生是多通道量子干涉的结果.利用缀饰态理论对acStark分裂给出很好的解释 关键词： 四能级系统模型 ac-Stark分裂 黑线(darkline) 多通道量子干涉     

Interacting ghost dark energy in Brans-Dicke theory

We investigate the QCD ghost model of dark energy in the framework of Brans-Dicke cosmology. First, we study the non-interacting ghost dark energy in a flat Brans-Dicke theory. In this case we obtain the equation of state and the deceleration parameters and a differential equation governing the evolution of ghost energy density. Interestingly enough, we find that the equation of state parameter of the non-interacting ghost dark energy can cross the phantom line (wD=−1) provided the parameters of the model are chosen suitably. Then, we generalize the study to the interacting ghost dark energy in both flat and non-flat Brans-Dicke framework and find out that the transition of wD to phantom regime can be more easily achieved for than when resort to the Einstein field equations is made.     

Instability of Interacting Ghost Dark Energy Model in an Anisotropic Universe

A new dark energy model called “ghost dark energy” was recently suggested to explain the observed accelerating expansion of the universe. This model originates from the Veneziano ghost of QCD. The dark energy density is proportional to Hubble parameter, ρ _Λ = α H, where α is a constant of order \({\Lambda }^{3}_{QCD}\) and Λ _{Q C D} ～ 100M e V is QCD mass scale. In this paper, we investigate about the stability of generalized QCD ghost dark energy model against perturbations in the anisotropic background. At first, the ghost dark energy model of the universe with spatial BI model with/without the interaction between dark matter and dark energy is discussed. In particular, the equation of state and the deceleration parameters and a differential equation governing the evolution of this dark energy model are obtained. Then, we use the squared sound speed \({v_{s}^{2}}\) the sign of which determines the stability of the model. We explore the stability of this model in the presence/absence of interaction between dark energy and dark matter in both flat and non-isotropic geometry. In conclusion, we find evidence that the ghost dark energy might can not lead to a stable universe favored by observations at the present time in BI universe.     

Holographic Dark Energy in Higher Derivative Gravity with Varying Gravitational Constant

In this paper we investigate the holographic dark energy scenario in higher derivative gravity with a varying gravitational constant. We introduce a kind of energy density from higher derivative gravity which has role of the same as holographic dark energy. We obtain the exact differential equation , which determine the evolution of the dark energy density based on varying gravitational constant G. We also find out a cosmological application of our work by evaluating a relation for the equation of state of dark energy for low redshifts containing varying G correction.     

Effects of Low Anisotropy on Generalized Ghost Dark Energy in Galileon Gravity

The definition of the Galileon gravity form is extended to the Brans-Dicke theory. Given, the framework of the Galileon theory, the generalized ghost dark energy model in an anisotropic universe is investigated. We study the cosmological implications of this model. In particular, we obtain the equation of state and the deceleration parameters and a differential equation governing the evolution of this dark energy in Bianchi type I model. We also probe observational constraints by using the latest observational data on the generalized ghost dark energy models as the unification of dark matter and dark energy. In order to do so, we focus on observational determinations of the Hubble expansion rate(namely, the expansion history) H(z). As a result, we show the influence of the anisotropy(although low) on the evolution of the universe in the statefinder diagrams for Galileon gravity.     

Sources of arbitrary states of coherence that generate completely coherent fields outside the source

A new theorem concerning nonradiating stochastic sources is derived. The theorem is used to describe sources that can have a variety of different states of coherence and yet each of them generating a field that is completely spatially coherent outside the source domain. The bearing of this result on a basic unsolved problem is spectroscopy of partially coherent sources is noted.     

原子相干对里德伯原子稳定性的影响

研究了含级联双光子过程的多束缚态激光场诱导原子连续态结构系统中原子的相干捕获,给出了产生相干捕获的条件及暗态的表达式,讨论了原子初态和激光强度对原子相干捕获及粒子布居值在束缚态上分布的影响,揭示了原子相干对稳定里德伯原子的重要作用。     

Holographic dark energy with varying gravitational constant

We investigate the holographic dark energy scenario with a varying gravitational constant, in flat and non-flat background geometry. We extract the exact differential equations determining the evolution of the dark energy density-parameter, which include G-variation correction terms. Performing a low-redshift expansion of the dark energy equation of state, we provide the involved parameters as functions of the current density parameters, of the holographic dark energy constant and of the G-variation.     

Polarization and intensity properties of converging J0-correlated Schell-model beams

Based on the cross-spectral density matrix, closed form result for propagation equation of electromagnetic J₀-correlated Schell-model beams (EJSMBs) through a paraxial optical system is obtained and the focusing properties are studied. Both numerical calculation and physical interpretation are obtained. It is found that a tunable dark hollow area, which has potential applications in optical trapping, can be obtained by altering the coherence parameter and the focal length. It is also shown that even though the original field is unpolarized, the beams can become fully polarized in the focal region with its width being tunable by changing the coherence parameter. The relevance of this work to applications such as coherent detection in optical communication is also discussed.     

铁基超导体FeSe0.5Te0.5表面隧道谱的研究

用扫描隧道显微镜/谱仪仔细研究了铁基超导单晶FeSe_0.5Te_0.5样品的表面形貌和隧道谱, 测量到了清晰的表面原子形貌和在空间比较稳定的隧道谱结构．在样品中测量的隧道谱零能态密度比较高, 说明样品里面有比较强的非弹性准粒子散射. 在正能5 mV附近有个较大的背景鼓包, 这一背景在很高温度也未消失. 空间中Se和Te集中的位置会带来高能背景的变化, 超导能隙附近谱的形状大致相同. 较强的非弹性准粒子散射破坏了超导的准粒子散射, 因此没有在二维微分电导图中发现超导准粒子相干散射的特征亮斑.     

Particle density and non-local kinetic energy density functional for two-dimensional harmonically confined Fermi vapors

We evaluate analytically some ground state properties of two-dimensional harmonically confined Fermi vapors with isotropy and for an arbitrary number of closed shells. We first derive a differential form of the virial theorem and an expression for the kinetic energy density in terms of the fermion particle density and its low-order derivatives. These results allow an explicit differential equation to be obtained for the particle density. The equation is third-order, linear and homogeneous. We also obtain a relation between the turning points of kinetic energy and particle densities, and an expression of the non-local kinetic energy density functional. Received 27 March 2001 and Received in final form 12 June 2001     

Electromagnetically induced quantum memory

We discuss the problem of creating coherence in an optically driven quantum system in conditions where decoherence is caused by the laser field itself, due to coupling of the system to a rapidly decaying state or continuum. It is shown that by applying an additional laser field between this state and a bound state the relaxation channel can be suppressed as a result of a "dark state" formation, giving rise to long living Rabi oscillations in the system. It is found that the same mechanism of preserving coherence exists in systems with level splitting or degeneracy, where the driving field interacts with multiple resonant sublevels simultaneously. We also show that specific coherent propagation phenomena assisted by the interference suppression of decoherence can be observed under these conditions.     

Y型四能级中的双电磁感应透明和超窄吸收

采用密度矩阵方程．对双光场耦合的分子Y型四能级系统的粒子数分布和吸收特性进行了计算和分析,在此能级系统中得到了双暗态共振和双电磁感应透明．并讨论了相应的物理机制。同时,我们讨论了Y型四能级两个上能级的自发辐射产生的量子干涉效应对电磁感应透明的影响,发现自发辐射干涉相消可以产生超窄线宽和导致探测光的吸收增强,自发辐射干涉相长可以展宽谱线和减弱探测光的吸收,并运用缀饰态理论对以上计算结果进行分析,与采用密度矩阵方程的计算结果一致。     

Propagating fronts and the center manifold theorem

We prove the existence of propagating front solutions for the Swift-Hohenberg equation (SH). Using the center manifold theorem we reduce the problem to a two dimensional system of ordinary differential equations. They describe stationary solutions and front solutions of the partial differential equation (SH). We identify the well-known amplitude equation as the lowest order approximation to the equation of motion on the center manifold.     

Binary Mixture of Perfect Fluid and Dark Energy in Modified Theory of Gravity

A self consistent system of Plane Symmetric gravitational field and a binary mixture of perfect fluid and dark energy in a modified theory of gravity are considered. The gravitational field plays crucial role in the formation of soliton-like solutions, i.e., solutions with limited total energy, spin, and charge. The perfect fluid is taken to be the one obeying the usual equation of state, i.e., p = γρ with γ∈ [0, 1] whereas, the dark energy is considered to be either the quintessence like equation of state or Chaplygin gas. The exact solutions to the corresponding field equations are obtained for power-law and exponential volumetric expansion. The geometrical and physical parameters for both the models are studied.     

Matrix method for the solution of RF field perturbations due to local frequency shifts

To tune the accelerating field to the design value in a periodical radio frequency accelerating structure, Slater's perturbation theorem is commonly used. This theorem solves a second-order differential equation to obtain the electrical field variation due to a local frequency shift. The solution becomes very difficult for a complex distribution of the local frequency shifts. Noticing the similarity between the field perturbation equation and the equation describing the transverse motion of a particle in a quadrupole channel, we propose in this paper a new method in which the transfer matrix method is applied to the field calculation instead of directly solving the differential equation. The advantage of the matrix method is illustrated in examples.     

Holographic Dark Energy Model with Time Varying G as Well as c 2 Parameter

In this paper, we study a holographic dark energy model with time varying gravitational constant G as well as holographic parameter c ² in flat FRW space-time geometry. We obtain the evolution of equation of state parameter and the exact differential equation, which determine the evolution of the dark energy density based on varying G and c ² parameter. Also, we determine the deceleration parameter to explain the expansion of the universe. Further, we study the validity of the generalized second law of thermodynamics in this scenario. Finally, we find out a cosmological implication of our work by evaluating the holographic dark energy equation of state for low red-shifts containing both varying G and c ² parameter corrections.