Double photoionization of helium atoms at 1 eV above threshold

An ab initio calculation of triple differential cross-section for double photoionization of helium atoms are presented for a very low energy of just 1 eV above threshold in the equal energy sharing kinematics. We have used hyperspherical partial wave theory together with a Numerov difference scheme in place of other schemes used in our earlier works. The results are in excellent qualitative agreement with the measurements of D?rner et al. [Phys. Rev. A 57, 1074 (1998)].     

Strong electron correlation in photoionization of spin-orbit doublets

A new and explicitly many-body aspect of the "leveraging" of the spin-orbit interaction is demonstrated, spin-orbit activated interchannel coupling, which can significantly alter the photoionization cross section of a spin-orbit doublet. As an example, it is demonstrated via a modified version of the spin-polarized random phase approximation with exchange, that a recently observed unexplained structure in the Xe 3d(5/2) photoionization cross section [A. Kivim?ki et al., Phys. Rev. A 63, 012716 (2000)] is entirely due to this effect. Similar features are predicted for Cs 3d(5/2) and Ba 3d(5/2).     

Collective modes and ballistic expansion of a fermi gas in the BCS-BEC crossover

We evaluate the frequencies of collective modes and the anisotropic expansion rate of a harmonically trapped Fermi superfluid at varying coupling strengths across a Feshbach resonance driving a BCS-BEC crossover. The equations of motion for the superfluid are obtained from a microscopic mean-field expression for the compressibility and are solved within a scaling ansatz. Our results confirm nonmonotonic behavior in the crossover region and are in quantitative agreement with current measurements of the transverse breathing mode by Kinast et al. [Phys. Rev. Lett. 92, 150402 (2004)]] and of the axial breathing mode by Bartenstein et al. [Phys. Rev. Lett. 92, 203201 (2004)]].     

Experimental demonstration of single photon nonlocality

In this Letter we experimentally implement a single photon Bell test based on the ideas of S. Tan et al. [Phys. Rev. Lett. 66, 252 (1991)]] and L. Hardy [Phys. Rev. Lett. 73, 2279 (1994)]]. A double homodyne measurement is used to measure correlations in the Fock space spanned by zero and one photons. Local oscillators used in the correlation measurement are distributed to two observers by copropagating it in an orthogonal polarization mode. This method eliminates the need for interferometrical stability in the setup, consequently making it a robust and scalable method.     

共面不对称条件下低能电子碰撞电离Ar(3p)的三重微分截面

采用修正的扭曲波玻恩近似方法, 在共面不对称几何条件下, 计算了能量为70.8 eV电子与Ar(3p)碰撞电离的(e, 2e)三重微分截面, 并与最新实验数据进行了比较. 结果表明电子交换效应和后碰撞相互作用在低能电子碰撞的(e, 2e)过程中起着重要作用. 关键词： (e,2e)三重微分截面 扭曲波玻恩近似 后碰撞相互作用 电子交换效应     

Measurement of angular dependence of M X-ray production cross-sections in Re,Bi and U at 5.96 keV

The M X-ray production differential cross sections in Re, Bi and U elements have been measured at the 5.96 keV incident photon energy in an angular range 135°–155°. The measurements were performed using a ⁵⁵Fe source and a Si(Li) detector. The present results contradict the predictions of Cooper and Zare [Atomic Collision Processes, Gordon and Breach, New York (1969)] and experimental results of Kumar et al. [J. Phys. B: At. Mol. Opt. 34, 613 (2001)]. that, after photoionization of inner shells, the vacancy state has equal population of magnetic substates and the subsequent X-ray emission is isotropic, but confirm the predictions of the calculations of Flügge et al. [Phys. Rev. Lett. 29, 7 (1972)] and experimental results of Sharma and Allawadhi [J. Phys. B: At. Mol. Opt. 32, 2343 (1999)] and Ertugrul [Nucl. Instrum. Meth. B 119, 345 (1996)]. Total M X-ray production cross sections from the decay at the 5.96 keV photon energies are found to be in good agreement with the calculated theoretical results using the theoretical values of M shell photoionization cross section.     

Onset of collective and cohesive motion

We study the onset of collective motion, with and without cohesion, of groups of noisy self-propelled particles interacting locally. We find that this phase transition, in two space dimensions, is always discontinuous, including for the minimal model of Vicsek et al. [Phys. Rev. Lett. 75, 1226 (1995)]] for which a nontrivial critical point was previously advocated. We also show that cohesion is always lost near onset, as a result of the interplay of density, velocity, and shape fluctuations.     

Experimental demonstration of continuous variable polarization entanglement

We report the experimental transformation of quadrature entanglement between two optical beams into continuous variable polarization entanglement. We extend the inseparability criterion proposed by Duan et al. [Phys. Rev. Lett. 84, 2722 (2000)]] to polarization states and use it to quantify the entanglement. We propose an elaboration utilizing two quadrature entangled pairs for which all three Stokes operators between a pair of beams are entangled.     

Continuous variable entanglement using cold atoms

We present an experimental demonstration of both quadrature and polarization entanglement generated via the interaction between a coherent linearly polarized field and cold atoms in a high finesse optical cavity. The nonlinear atom-field interaction produces two squeezed modes with orthogonal polarizations which are used to generate a pair of nonseparable beams, the entanglement of which is demonstrated by checking the inseparability criterion for continuous variables recently derived by Duan et al. [Phys. Rev. Lett. 84, 2722 (2000)]] and calculating the entanglement of formation [Phys. Rev. Lett. 91, 107901 (2003)]].     

Ab initio calculation of photoionization and inelastic photon scattering spectra of He below the N=2 threshold in a dc electric field

We study the Stark effect on doubly excited states of the helium atom below N=2. We present the ab initio photoionization and total inelastic photon scattering cross sections calculated with the method of complex scaling for field strengths F 相似文献   

Where is the shot noise of a quantum point contact?

Reznikov et al. [Phys. Rev. Lett. 75, 3340 (1995)]] have presented definitive observations of nonequilibrium noise in a quantum point contact. Especially puzzling is the "anomalous" peak structure of the excess noise measured at constant current; to date it remains unexplained. We show that their experiment directly reveals the deep link between conservation principles in the electron gas and its low-dimensional, mesoscopic behavior. The keys to that connection are gauge invariance and the compressibility sum rule. These are central not only to the experiment of Reznikov et al., but to the very nature of all mesoscopic transport.     

Nonperturbative treatment of ionization with excitation of helium by electron impact

We present cross sections for electron-impact ionization and simultaneous ionization plus excitation of helium by electron impact. The results are obtained from a fully nonperturbative close-coupling formalism using our B-spline R-matrix approach. A large number of pseudostates in the expansion of the wave function represent the coupling to the ionization continuum. We obtain excellent agreement with the directly measured experimental cross section ratios (Bellm et al., Phys. Rev. A 75, 042704 (2007)) for ionization leaving the residual He? ion in either the 1s ground state or the n = 2 (2s + 2p) excited states.     

Sub- and superluminal propagation of intense pulses in media with saturated and reverse absorption

We develop models for the propagation of intense pulses in solid state media which can have either saturated absorption or reverse absorption. We model subluminal propagation in ruby and superluminal propagation in alexandrite as three and four level systems, respectively, coupled to Maxwell's equations. We present results well beyond the traditional pump-probe approach and explain the experiments of Bigelow et al. [Phys. Rev. Lett. 90, 113903 (2003)]Science 301, 200 (2003)]] on solid state materials.     

Ray-splitting correction to the Weyl formula: experiment versus theory

An abrupt change in the dielectric constant of media filling a microwave cavity was predicted by Prange et al. [Phys. Rev. E 53, 207 (1996)]] to produce a ray splitting correction to the Weyl formula for the mean staircase function of resonances. We present the first experimental confirmation of this effect. Our results with a quasi-two-dimensional cavity are directly relevant to the ray-splitting correction in two-dimensional quantal ray-splitting billiards.     

Coupled-Channel Optical Calculations for e＋-Rb Collision at Intermediate Energies

We present the calculation of total cross sections for positron scattering by Rb at intermediate energies by using the coupled-channel optical method, in which an equivalent-local optical potential has been used to describe the continuum and rearrangement process. The present total cross sections are in good agreement with the measurements of Parikh et al. [Phys. Rev. A 47 （1993） 1535] and other theoretical calculation results. Our results show three peaks in the vicinity of 47eV, which have not been found in the previous measurements and theoretical calculations.     

Method for calculating photoionization cross sections of fullerenes in the local density and random phase approximations

A method for calculating the photoionization cross sections of fullerenes taking into account many-electron correlations on the basis of the local density and random phase approximations is proposed and implemented. Calculations are made specifically for fullerenes C₆₀ and C₂₀. It is shown that the photoionization spectrum of C₆₀ acquires a plasmon resonance whose position and magnitude are in good agreement with experimental results [I.V. Hertel, H. Steger, J. de Vries et al., Phys. Rev. Lett. 68, 784 (1992)] and with the results of other calculations [M.J. Puska and R.N. Nieminen, Phys. Rev. A47, 1181 (1993)]. The emergence of a giant resonance is predicted in the photoionization spectrum of fullerene C₂₀ with the center at a photon energy on the order of 27 eV, which corresponds to the frequency of resonant surface plasmon oscillations in a conducting sphere.     

Dynamical overstability of radiative blast waves: the atomic physics of shock stability

Atomic-physics calculations of radiative cooling are used to develop criteria for the overstability of radiating shocks. Our calculations explain the measurement of shock overstability by Grun et al. [Phys. Rev. Lett. 66, 2738 (1991)]] and explain why the overstability was not observed in other experiments. The methodology described here can be especially useful in astrophysical situations where the relevant properties leading to an overstability can be measured spectroscopically, but the effective adiabatic index is harder to determine.     

Multiple series of shape resonances and near-zero-energy cross section enhancements in photoionization of hydrogen-like ions with screened coulomb interaction

The recently discovered multiple series of shape resonances and near-zero-energy enhancements in photoionization cross section of hydrogen-like atomic systems with screened Coulomb (Yukawa type) interaction [Phys. Rev. A 80, 063404 (2009)] are studied in detail, in particular their evolution with the variation of the screening strength of the potential. The conditions for appearance of these multiple series of cross section features are identified and related to certain critical screening strengths of the potential. A relation between the appearance of Cooper minima and shape resonaces in the photoionizations cross section has been established. It is also shown that the s-channel of np photoionization for a fixed photoelectron energy exhibits Ramsauer-Townsend minima in the screening length variable.     

Two-band superconductivity in MgB2

The study of the anisotropic superconductor MgB2 using a combination of scanning tunneling microscopy and spectroscopy reveals two distinct energy gaps at Delta(1)=2.3 meV and Delta(2)=7.1 meV at 4.2 K. Different spectral weights of the partial superconducting density of states are a reflection of different tunneling directions in this multiband system. Temperature evolution of the tunneling spectra follows the BCS scenario [Phys. Rev. Lett. 3, 552 (1959)]] with both gaps vanishing at the bulk T(c). The data confirm the importance of Fermi-surface sheet dependent superconductivity in MgB2 proposed in the multigap model by Liu et al. [Phys. Rev. Lett. 87, 087005 (2001)]].     

Experimental observation of interatomic coulombic decay in neon dimers

Recently Cederbaum et al. [Phys. Rev. Lett. 79, 4778 (1997)]] predicted a new decay channel of excited atoms and molecules termed interatomic Coulombic decay (ICD). In ICD the deexcitation energy is transferred via virtual photon exchange to a neighboring atom, which releases it by electron emission. We report on an experimental observation of ICD in 2s ionized neon dimers. The process is unambiguously identified by detecting the energy of two Ne1+ fragments and the ICD electron in coincidence, yielding a clean, background free experimental spectral distribution of the ICD electrons.