Three-dimensional simulations of ion acceleration from a foil irradiated by a short-pulse laser

Using 3D particle-in-cell simulations we study ion acceleration from a foil irradiated by a laser pulse at 10(19) W/cm(2) intensity. At the front side, the laser ponderomotive force pushes electrons inwards, thus creating the electric field by charge separation, which drags the ions. At the back side of the foil, the ions are accelerated by space charge of the hot electrons exiting into vacuum, as suggested by Hatchett et al. [Phys. Plasmas 7, 2076 (2000)]. The transport of hot electrons through the overdense plasma and their exit into vacuum are strongly affected by self-generated magnetic fields. The fast ions emerge from the rear surface in cones similar to those detected by Clark et al. [Phys. Rev. Lett. 84, 670 (2000)].     

Positronium Decay in a Circular Polarized Laser Field

We calculate the lifetime of both the o-Ps and the p-Ps positronium annihilation decay Ps→γγ in the strong circular polarized laser field. We take a strategy of the factorization to separate the effects caused by the Coulomb interaction and the strong laser field interaction. It is factorized in the time direction but not in the space direction. Our results show that in the laser with long wavelength and high intensity, the lifetimes of those Ps states are dramatically increased. For CO₂ laser with 10 μm wavelength and 10¹³ W/cm² intensity, lifetime of the spin-single positronium is increased by 10⁸ times. Our result is consistent with those obtained by solving the Schödinger equation. This effect may be useful for the high harmonic generation (HHG) effects provided with the Ps [Phys. Rev. Lett. 70 (1993) 774; Phys. Rev. Lett. 93 (2004) 013601].     

Atomic structure effects of a target on the polarization properties of high harmonics in the region of the cooper minimum

Recently, a scheme based on the method of weak measurements to register the trajectories of photons passing through a nested Mach–Zehnder interferometer was proposed [L. Vaidman, Phys. Rev. A 87, 052104 (2013)] and then realized [A. Danan, D. Farfurnik, S. Bar-Ad, et al., Phys. Rev. Lett. 111, 240402 (2013)]. Interpreting the results of the experiment, the authors concluded that “the photons do not always follow continuous trajectories.” It is shown in this work that these results can be easily and clearly explained in terms of traditional classical electrodynamics or quantum mechanics implying the continuity of all possible paths of photons. Consequently, a new concept of disconnected trajectories proposed by the authors of work [Phys. Rev. Lett. 111, 240402 (2013)] is unnecessary.     

Long-lived excited states at surfaces: Cs/Cu(111) and Cs/Cu(100) systems

One-electron and multielectron contributions to the decay of transient states in the Cs/Cu(111) and (100) systems are studied by a joined wave-packet propagation and many-body metal response approach. The long lifetime of these states is due to the Cu L and X band gaps which reduce the electron tunneling between Cs and Cu. In the (111) case, the decay is mainly by inelastic e-e interaction, whereas in the (100) case, electron tunneling is dominating. This accounts very well for the experimental findings [Bauer et al., Phys. Rev. B 55, 10 040 (1997) and Ogawa et al., Phys. Rev. Lett. 82, 1931 (1999)].     

Diffraction of picosecond bulk longitudinal and shear waves in micron thick films

Investigation of thin metallic film properties by means of picosecond ultrasonics [C. Thomsen et al., Phys. Rev. Lett. 53, 989 (1984)] has been under the scope of several studies. Generation of longitudinal and shear waves [T. Pézeril et al., Phys. Rev. B 73, 132301 (2006); O. Matsuda et al., Phys. Rev. Lett. 93, 095501 (2004)] with a wave vector normal to the film free surface has been demonstrated. Such measurements cannot provide complete information about properties of anisotropic films. Extreme focusing of a laser pump beam (≈0.5 μm) on the sample surface has recently allowed us to provide evidence of picosecond acoustic diffraction in thin metallic films (≈1 μm) [C. Rossignol et al., Phys. Rev. Lett. 94, 166106 (2005)]. The resulting longitudinal and shear wavefronts propagate at group velocity through the bulk of the film. To interpret the received signals, source directivity diagrams are calculated taking into account material anisotropy, optical penetration, and laser beam width on the sample surface. It is shown that acoustic diffraction increases with optical penetration, so competing with the increasing of directivity caused by beam width. Reflection with mode conversion at the film-substrate interface is discussed.     

Quenched noise in surface growth

The analytical continuous equations for the Tang and Leschhorn (Phys. Rev. A 45 (1992) R8309) and the Buldyrev et al. (Phys. Rev. A 45 (1992) R8313) models are derived from the microscopic rules using a regularization procedure. As was shown in a previous paper (Phys. Rev. E 62 (2000) 6970) the continuous equation for the Tang and Leschhorn model is formally different to the Kardar–Parisi–Zhang equation (Phys. Rev. Lett. 56 (1986) 889) with quenched noise (QKPZ). Nevertheless, after expanding the multiplicative noise, it is shown that we recover the usual QKPZ, demonstrating analytically that both equations belong to the same universality class.     

Stabilisation of alkali-adsorbate-induced states on Cu(111) surfaces

The Li and Cs alkali-adsorbate-induced states on a model Cu(111) surface are studied theoretically using the coupled angular mode and the wave packet propagation methods. Their energy position and their decay rate via one-electron transfer into the metal are calculated. An unoccupied alkali-induced state is found with a rather long lifetime, much longer than those found in the case of free-electron metal surfaces. This is attributed to the combined effect of the hybridisation of the alkali levels and of the Cu(111) projected band gap along the normal to the surface that blocks the electron transfer between the adsorbate and the metal. This qualitatively explains the experimental finding of a long-lived state by Bauer et al. [Phys. Rev. B 55 (1997) 10 040] and Ogawa et al. [Phys. Rev. Lett. 82 (1999) 1931].     

Vibrational excitation of diatomic molecular ions in strong field ionization of diatomic molecules

A model based on the strong-field and Born-Oppenheimer approximations qualitatively describes the distribution over vibrational states formed in a diatomic molecular ion following ionization of the neutral molecule by intense laser pulses. Good agreement is found with a recent experiment [X. Urbain et al., Phys. Rev. Lett. 92, 163004 (2004)]. In particular, the observed deviation from a Franck-Condon-like distribution is reproduced. Additionally, we demonstrate control of the vibrational distribution by a variation of the peak intensity or a change of frequency of the laser pulse.     

Rydberg cold collisions dominated by ultralong range potential

In this work we measure the time evolution of the population resulting from energy-transfer collisions as a function of the energy difference between the entrance and exit collisional channels using a sample of cold Rydberg atoms produced in a rubidium magneto-optical trap. The 34S(1/2) population, produced by collisions between atoms in the 33P(3/2) state, is monitored as a function of time through the pulsed-field ionization technique. The experimental results are compared with a recent published model based on a two-body interaction considering an attractive potential [Phys. Rev. A 65, 023405 (2002)]]; which is calculated according to a recent Letter by Boisseau et al. [Phys. Rev. Lett. 88, 133004 (2002)]]. The agreement is remarkable, which suggests the existence of such ultralong range potential proposed by Boisseau et al.     

Image state linewidth on Ag(100) studied by two-photon photoemission spectroscopy

The linewidth of the first image state on Ag(100) was studied using two-photon photoemission spectroscopy. The width was found to be 35±9 meV in agreement with a recent time-resolved study (Schoenlein et al.: Phys. Rev. Lett.61, 2596 (1988)) but somewhat larger than the theoretical value of 10–20 meV (Echenique et al.: Phys. Rev. B35, 4529 (1987)).     

Generalized statistical complexity measures: Geometrical and analytical properties

We discuss bounds on the values adopted by the generalized statistical complexity measures [M.T. Martin et al., Phys. Lett. A 311 (2003) 126; P.W. Lamberti et al., Physica A 334 (2004) 119] introduced by López Ruiz et al. [Phys. Lett. A 209 (1995) 321] and Shiner et al. [Phys. Rev. E 59 (1999) 1459]. Several new theorems are proved and illustrated with reference to the celebrated logistic map.     

Two-dimensional foam rheology with viscous drag

We formulate and apply a continuum model that incorporates elasticity, yield stress, plasticity, and viscous drag. It is motivated by the two-dimensional foam rheology experiments of Debregeas et al. [Phys. Rev. Lett. 87, 178305 (2001)10.1103/PhysRevLett.87.178305] and Wang et al. [Phys. Rev. E 73, 031401 (2006)10.1103/PhysRevE.73.031401], and is successful in exhibiting their principal features, which are an exponentially decaying velocity profile and strain localization. Transient effects are also identified.     

Comment on breakup densities of hot nuclei

In [V.E. Viola et al., Phys. Rev. Lett. 93 (2004) 132701, D.S. Bracken et al., Phys. Rev. C 69 (2004) 034612] the observed decrease in spectral peak energies of IMFs emitted from hot nuclei was interpreted in terms of a breakup density that decreased with increasing excitation energy. Subsequently, Raduta et al. [Ad. Raduta et al., Phys. Lett. B 623 (2005) 43] performed MMM simulations that showed decreasing spectral peaks could be obtained at constant density. In this Letter we point out that this apparent inconsistency is due to a selective comparison of theory and data that overlooks the evolution of the fragment multiplicities as a function of excitation energy.     

Quantum entanglement formation by repeated spin blockade measurements in a spin field-effect transistor structure embedded with quantum dots

We propose a method of operating a quantum state machine made of stacked quantum dots buried in adjacent to the channel of a spin field-effect transistor (FET) [S. Datta, B. Das, Appl. Phys. Lett. 56 (1990) 665; K. Yoh, et al., Proceedings of the 23rd International Conference on Physics of Semiconductors (ICPS) 2004; H. Ohno, K. Yoh et al., Jpn. J. Appl. Phys. 42 (2003) L87; K. Yoh, J. Konda, S. Shiina, N. Nishiguchi, Jpn. J. Appl. Phys. 36 (1997) 4134]. In this method, a spin blockade measurement extracts the quantum state of a nearest quantum dot through Coulomb blockade [K. Yoh, J. Konda, S. Shiina, N. Nishiguchi, Jpn. J. Appl. Phys. 36 (1997) 4134; K. Yoh, H. Kazama, Physica E 7 (2000) 440] of the adjacent channel conductance. Repeated quantum Zeno-like (QZ) measurements [H. Nakazato, et al., Phys. Rev. Lett. 90 (2003) 060401] of the spin blockade is shown to purify the quantum dot states within several repetitions. The growth constraints of the stacked InAs quantum dots are shown to provide an exchange interaction energy in the range of 0.01–1 meV [S. Itoh, et al., Jpn. J. Appl. Phys. 38 (1999) L917; A. Tackeuchi, et al., Jpn. J. Appl. Phys. 42 (2003) 4278]. We have verified that one can reach the fidelity of 90% by repeating the measurement twice, and that of 99.9% by repeating only eleven QZ measurements. Entangled states with two and three vertically stacked dots are achieved with the sampling frequency of the order of 100 MHz.     

Random matrix theory for closed quantum dots with weak spin-orbit coupling

To lowest order in the coupling strength, the spin-orbit coupling in quantum dots results in a spin-dependent Aharonov-Bohm flux. This flux decouples the spin-up and spin-down random matrix theory ensembles of the quantum dot. We employ this ensemble and find significant changes in the distribution of the Coulomb blockade peak height, in particular, a decrease of the width of the distribution. The puzzling disagreement between standard random matrix theory and the experimental distributions by Patel et al. [Phys. Rev. Lett. 81, 5900 (1998)]] might possibly be attributed to these spin-orbit effects.     

Laser field absorption in self-generated electron-positron pair plasma

Recently, much attention has been attracted to the problem of limitations on the attainable intensity of high power lasers [A.?M. Fedotov et al., Phys. Rev. Lett. 105, 080402 (2010)]. The laser energy can be absorbed by electron-positron pair plasma produced from a seed by a strong laser field via the development of the electromagnetic cascades. The numerical model for a self-consistent study of electron-positron pair plasma dynamics is developed. Strong absorption of the laser energy in self-generated overdense electron-positron pair plasma is demonstrated. It is shown that the absorption becomes important for a not extremely high laser intensity I ～ 10(24) W/cm(2) achievable in the near future.     

Shape Coexistence for 179Hg in Relativistic Mean-Field Theory

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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)]].     

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)]].     

Hosing instability in the blow-out regime for plasma-wakefield acceleration

The electron hosing instability in the blow-out regime of plasma-wakefield acceleration is investigated using a linear perturbation theory about the electron blow-out trajectory in Lu et al. [in Phys. Rev. Lett. 96, 165002 (2006)10.1103/PhysRevLett.96.165002]. The growth of the instability is found to be affected by the beam parameters unlike in the standard theory Whittum et al. [Phys. Rev. Lett. 67, 991 (1991)10.1103/PhysRevLett.67.991] which is strictly valid for preformed channels. Particle-in-cell simulations agree with this new theory, which predicts less hosing growth than found by the hosing theory of Whittum et al.