Generation of ultrashort ultraviolet (uv) pulses by using nonlinear frequency conversion through filamentation was experimentally and theoretically investigated. By gently focusing second harmonic and fundamental Ti:sapphire laser pulses into gases, ultrashort uv pulses were efficiently generated by four-wave mixing processes through filamentation. The pressure dependence of the conversion efficiency cannot be explained by a one-dimensional model, but calculation of multicolor filament by a three-dimensional model was successful. The simulation result indicates a broad scalability of the scheme for frequency conversion of ultrashort pulses. The generated two-color uv pulses (200 and 260 nm) were successfully compressed down to $\sim 15\text{fs}$.

This paper reports improved reconstruction of complex wave fields from extended objects. The combination of ptychography with Fresnel diffractive imaging results in better reconstructions with fewer iterations required to convergence than either method considered separately. The method is applied to retrieve the projected thickness of a gold microstructure and comparative results using ptychography and Fresnel diffractive imaging are presented.

The asymptotic expansion method based on a core polarization potential for the Rydberg electron is reviewed and extended to the high angular momentum states of helium up to $L=15$. A comparison with recent large-scale configuration interaction calculations for the nonrelativistic energies shows that there is good agreement for $L=7$, but there are serious systematic disagreements for the states of higher angular momentum. A possible explanation is that there is an important class of configurations missing from the CI calculations.

Our calculations have shown that the $5f_{5/2}\text{−}7s_{1/2}$ $23131{\text{cm}}^{-1}$ transition from the ground state in the ion ${\text{Th}}^{3+}$ is very sensitive to the temporal variation of the fine-structure constant $\alpha =e^2/\hslash c$ $\left(q=-75300{\text{cm}}^{-1}\right)$. The line is very narrow, the ion has been trapped and laser cooled, and the positive shifter line $5f_{5/2}\text{−}5f_{7/2}$ $4325{\text{cm}}^{-1}$ $\left(q=+2900{\text{cm}}^{-1}\right)$ may be used as a reference. A comparison may also be made with a positive shifter in another atom or ion. This makes ${\text{Th}}^{3+}$ a good candidate to search for the $\alpha$ variation.

Using the Born-Oppenheimer approximation, we derive an effective Hamiltonian for an optomechanical system that leads to a nonlinear Kerr effect in the system’s vacuum. The oscillating mirror at one edge of the optomechanical system induces a squeezing effect in the intensity spectrum of the cavity field. A near-resonant laser field is applied at the other edge to drive the cavity field in order to enhance the Kerr effect. We also propose a quantum-nondemolition-measurement setup to monitor a system with two cavities separated by a common oscillating mirror based on our effective Hamiltonian approach.

In a recent Comment [I. Brevik and S. A. Ellingsen, Phys. Rev. A 79, 027801 (2009)], our position that the calculation of dispersion forces should be based preferably on the Lorentz force (or, equivalently, on Maxwell’s stress tensor) is put into question, and it is argued that one should resort to Minkowski’s stress tensor instead. After sketching briefly our reasons for preferring the Lorentz force, we point out that by use of Minkowski’s stress tensor additional, compensatory force components are included in the calculation, but inconsistently. We consider the electrostatic arguments given in support of Minkowski’s tensor in the Comment as unconvincing, and we point out that the issue of divergences raised in the Comment in the context of planar setups is not specific to Maxwell’s stress tensor.

A high-resolution $\left(\Delta E\sim 55\text{meV}\right)$ trap-based positron beam has been used to measure absolute scattering cross sections for the excitation of the resolved $2{}^{1}S,P$ states of helium at energies between threshold and 38 eV. The experimental integral cross sections, which have typical uncertainties of 10% or less, are compared with several theoretical calculations, and the agreement is generally very favorable. In particular, a new convergent close-coupling approach shows excellent agreement with the experimental data.

A quantum-mechanical approach to ion-molecule collisions is presented. It involves a separation of molecular geometry and collision dynamics and enables the use of the basis generator method developed for ion-atom collisions with relatively minor modifications. As a first application, we consider the $p{\text{-H}}_2\text{O}$ collision system in the impact energy range of 20–5000 keV, and we report total cross sections for net electron transfer and ionization. They are in remarkably good agreement with experimental data.

A method for complete characterization of the waveform of individual few-cycle laser pulses is presented. By analyzing the “left” and “right” asymmetries of high-energy photoelectrons along the polarization axis using the recently developed quantitative rescattering theory, we show that the carrier-envelope phase (CEP), pulse duration, and peak intensity of each single-shot pulse can be readily retrieved. By CEP tagging each laser shot, the method permits the study of waveform-dependent processes be extended to relativistic beams and to wavelengths, where CEP stabilization is not yet possible.

We demonstrate a two-dimensional atom interferometer in a harmonic magnetic waveguide using a Bose-Einstein condensate. Such an interferometer could measure rotation using the Sagnac effect. Compared to free space interferometers, larger interactions times and enclosed areas can in principle be achieved, since the atoms are not in free fall. In this implementation, we induce the atoms to oscillate along one direction by displacing the trap center. We then split and recombine the atoms along an orthogonal direction using an off-resonant optical standing wave. We enclose a maximum effective area of $0.1{\text{mm}}^2$ limited by fluctuations in the initial velocity and by the coherence time of the interferometer. We argue that this arrangement is scalable to enclose larger areas by increasing the coherence time and then making repeated loops.

We report a unified representation of the spatial and angular Goos-Hänchen and Imbert-Fedorov shifts that occur when a light beam reflects from a plane interface. We thus reveal the dual nature of spatial and angular shifts in optical beam reflection. In the Goos-Hänchen case we show theoretically and experimentally that this unification naturally arises in the context of reflection from a lossy surface (e.g., a metal).

The Raman gain of a probe light in a three-state $\Lambda$ scheme placed into a defect of a one-dimensional photonic crystal is studied theoretically. We show that there exists a pump intensity range, where the transmission and reflection spectra of the probe field exhibit simultaneously occurring narrow peaks (resonances) whose position is determined by the Raman resonance. Transmission and reflection coefficients can be larger than unity at pump intensities on the order of tens of $\mu \text{W}/{\text{cm}}^2$. When the pump intensity is outside this region, the peak in the transmission spectrum turns into a narrow dip. The nature of narrow resonances is attributed to a drastic dispersion of the nonlinear refractive index in the vicinity of the Raman transition, which leads to a significant reduction in the group velocity of the probe wave.

We suggest possibilities for manipulation and ground-state cooling of micromechanical oscillators by resonant coupling of the mirror vibrations to narrow optical transitions of a designed material ensemble within a cavity mode. Particles, modeled as a two-level ensemble, create intracavity narrow bandwidth loss or gain and induce tailored asymmetric structuring of the cavity noise spectrum interacting with the oscillator. This facilitates cooling via inhibition of the Stokes-scattering process or enhancement of anti-Stokes scattering even for short low-finesse optical cavities.

We compare the creation rates for particle-antiparticle pairs produced by a supercritical force field for fermionic and bosonic model systems. The rates obtained from the Dirac and Klein-Gordon equations can be computed directly from the quantum-mechanical transmission coefficients describing the scattering of an incoming particle with the supercritical potential barrier. We provide a unified framework that shows that the bosonic rates can exceed the fermionic ones, as one could expect from the Pauli-exclusion principle for the fermion system. This imbalance for small but supercritical forces is associated with the occurrence of negative bosonic transmission coefficients of arbitrary size for the Klein-Gordon system, while the Dirac coefficient is positive and bound by unity. We confirm the transmission coefficients with time-dependent scattering simulations. For large forces, however, the fermionic and bosonic pair-creation rates are surprisingly close to each other. The predicted pair creation rates also match the slopes of the time-dependent particle probabilities obtained from large-scale ab initio numerical simulations based on quantum field theory.

We study maximally multipartite-entangled states in the context of Gaussian continuous variable quantum systems. By considering multimode Gaussian states with constrained energy, we show that perfect maximally multipartite-entangled states, which exhibit the maximum amount of bipartite entanglement for all bipartitions, only exist for systems containing $n=2$ or 3 modes. We further numerically investigate the structure of these states and their frustration for $n\le 7$.

Qutrits, the triple level quantum systems in various forms, have been proposed for quantum information processing recently. By the methods presented in this paper, a biphotonic qutrit, which is encoded with the polarizations of two photons in the same spatial-temporal mode, can be mapped to a single-photon qutrit in spatial modes. It will make arbitrary unitary operation on such biphotonic qutrit possible if we can also realize the inverse map to polarization space. Among the two schemes proposed in this paper, the one based only on linear optics realizes an arbitrary U(3) operation with a very small success probability. However, if added with weak nonlinearity, the success probability can be greatly improved. These schemes are feasible with the current experimental technology.

We address the classical capacity of a quantum bosonic memory channel with additive noise, subject to an input energy constraint. The memory is modeled by correlated noise emerging from a Gauss-Markov process. Under reasonable assumptions, we show that the optimal modulation results from a “quantum water-filling” solution above a certain input energy threshold, similar to the optimal modulation for parallel classical Gaussian channels. We also derive analytically the optimal multimode input state above this threshold, which enables us to compute the capacity of this memory channel in the limit of an infinite number of modes. The method can also be applied to a more general noise environment which is constructed by a stationary Gauss process. The extension of our results to the case of broadband bosonic channels with colored Gaussian noise should also be straightforward.

We provide a class of indecomposable entanglement witnesses. In $4\times 4$ case, it reproduces the well-known Breuer-Hall witness. We prove that these witnesses are optimal and atomic, i.e., they are able to detect the “weakest” quantum entanglement encoded into states with positive partial transposition. Equivalently, we provide a construction of indecomposable atomic maps in the algebra of $2k\times 2k$ complex matrices. It is shown that their structural physical approximations give rise to entanglement breaking channels. This result supports recent conjecture by Korbicz et al. [Phys. Rev. A 78, 062105 (2008)].

Static dipole polarizabilities are calculated in the ground and metastable states of ${\text{Sr}}^{+}$, ${\text{Ba}}^{+}$ and ${\text{Ra}}^{+}$ using the relativistic coupled-cluster method. Trends of the electron correlation effects are investigated in these atomic ions. We also estimate the Stark and black-body radiation shifts from these results for these systems for the transitions proposed for the optical frequency standards and compare them with available experimental data.