A merged beams technique has been used to investigate collisions between electrons and $\text{Si}_2{}^{-}$ ions over a relative kinetic energy range of 0–210 eV. Absolute cross sections for pure electron detachment, detachment plus dissociation, and dissociation involving atomic and ionic products were measured. The dominant process over the energy range studied is pure electron detachment. A search for a resonance associated with a ${\text{Si}}_2$ dianion was made but none was observed.

Ultracold bosons in rotating ring lattices have previously been shown to form macroscopic superpositions of different quasimomentum states. We demonstrate that the generation of this kind of state using slightly nonuniform ring lattices has several advantages: the energy gap decreases less severely with increasing number of particles, the sensitivity to detunings from the critical rotation frequency is reduced, and the scheme is not limited to commensurate filling. We show that different quasimomentum states can be distinguished in time-of-flight absorption imaging and propose to probe correlations via the many-body oscillations induced by a sudden change in the rotation frequency.

We theoretically study the possibility of reaching the antiferromagnetic phase of the Hubbard model by starting from a normal gas of trapped fermionic atoms and adiabatically ramping up an optical lattice. Requirements on the initial temperature and the number of atoms are determined for a three-dimensional square lattice by evaluating the Néel state entropy, taking into account fluctuations around the mean-field solution. We find that these fluctuations place important limitations on adiabatically reaching the Néel state.

We present a scheme for conditionally teleporting an unknown atomic state in cavity QED, which requires two atoms and one cavity mode. The translational degrees of freedom of the atoms are taken into account using the optical Stern-Gerlach model. We show that successful teleportation with probability 1/2 can be achieved through local measurements of the cavity photon number and atomic positions. Neither direct projection onto highly entangled states nor holonomous interaction-time constraints are required.

We make corrections to the paper of Andrzejewski et al. [Phys. Rev. A 76, 032110 (2007)].

In the preceding Comment, two points are raised.

We describe a theoretical method to distinguish between the precursors (transient part) and main signal (steady state) for a Gaussian pulse propagating through an anomalously dispersive linear dielectric. According to conventional theory of optical precursors, there is no main signal for Gaussian pulse propagation regardless of the system parameters. In this paper, we show the existence of the main pulse by comparing the conventional asymptotic theory with recently published analytical expressions. Additionally, we show that experimentally observed, asymmetrically extended tails in Gaussian pulse propagation are due to a resonant precursor.

We show how to implement several continuous-variable coherent protocols with linear optics. Noise can accumulate when implementing each coherent protocol with realistic optical devices. Our analysis bounds the level of noise accumulation. We highlight the connection between a coherent channel and a nonlocal quantum nondemolition interaction and give two new protocols that implement a coherent channel. One protocol is superior to a previous method for a nonlocal quantum nondemolition interaction because it requires fewer communication resources. We then show how continuous-variable coherent superdense coding implements two nonlocal quantum nondemolition interactions with a quantum channel and bipartite entanglement. We finally show how to implement continuous-variable coherent teleportation experimentally and provide a way to verify the correctness of its operation.

We theoretically demonstrate the selective enhancement of high-order harmonic generation (HHG) in two-color laser fields consisting of a single-cycle fundamental wave ($800\mathrm{nm}$ wavelength) and a multicycle subharmonic wave ($2400\mathrm{nm}$ wavelength). By performing time-frequency analyses based on a single-active-electron model, we reveal that such an enhancement is a result of the modified electron trajectories in the two-color field. Furthermore, we show that selectively enhanced HHG gives rise to a bandwidth-controllable extreme ultraviolet supercontinuum in the plateau region, facilitating the generation of intense single isolated attosecond pulses.

We investigate the optical transmission properties of a combined system which consists of two quantum-dot–nanocavity subsystems indirectly coupled to a waveguide in a planar photonic crystal. A Mollow-like triplet and the growth of sidebands are found, reflecting intrinsic optical responses in the complex microstructure.

We present an experimental system to generate large cross-phase modulation (XPM) in cold rubidium atoms. By using an efficient state-preparation technique in the ${}^{87}\mathrm{Rb}$ $D1$ line, an ideal four-level tripod-type atomic system is formed, which generates large cross-Kerr nonlinearity via interacting dark states in this system. The induced phase shift due to XPM for the probe beam is measured for different trigger beam intensities, which is the key to achieving conditional quantum phase gates and many other applications in quantum information processing.

We study entanglement witnesses that can be constructed with regard to the geometrical structure of the Hilbert-Schmidt space, i.e., we present how to use these witnesses in the context of quantifying entanglement and the detection of bound entangled states. We give examples for a particular three-parameter family of states that are part of the magic simplex of two-qutrit states.

Ali et al. [Phys. Rev. A 75, 042110 (2007)] have claimed that empirically testable differences exist between the quantum and semiclassical time of flight distribution for cold trapped atoms. We believe these claims to be misleading. For the particular case of noninteracting bosonic particles released from a harmonic trapping potential, we show that the quantum and semiclassical calculations for the time-of-flight distribution are equivalent, provided one is not too close to the quantum degeneracy point.

In their comment Gomes et al. [Phys. Rev. A 77, 026101 (2008)] have questioned the possibility of empirically testable differences existing between the semiclassical time of flight distribution for cold trapped atoms and a quantum distribution discussed by us recently [Ali et al., Phys. Rev. A 75, 042110 (2007).]. We argue that their criticism is based on a semiclassical treatment having restricted applicability for a particular trapping potential. Their claim does not preclude, in general, the possibility of differences between the semiclassical calculations and fully quantum results for the arrival time distribution of freely falling atoms.

We propose a different approach to obtain phase-matched generation of high-order harmonics based on the use of pulsed Bessel beams as pump pulses. By means of the “coherence map” technique, we show that it is possible to maximize the generation of a chosen harmonic of interest by properly adjusting the phase front tilt of the pulsed Bessel beam to compensate the mismatch arising from material and plasma dispersion and atomic phase.

Total and state selective $nl$-electron capture cross sections are presented for highly charged ions $Z=4–10$, 14, 18, and 26 colliding with water molecules. The energy range investigated was from $10\mathrm{eV}∕\mathrm{amu}$ $(v=0.02\mathrm{a.u.})\text{to}100\mathrm{keV}∕\mathrm{amu}$ $(v=2\mathrm{a.u.})$. An initialization for the $1B1$ and $3A1$ orbitals of the water molecule is introduced based on the one center expansion of Moccia and compared to our previous studies based on a hydrogenic approximation within the microcanonical ensemble. The $Z$ dependence of the calculated total cross sections is in reasonable agreement with the recent data of Mawhorter et al. [Phys. Rev. A 75, 032704 (2007)] and is improved over previous results. The energy dependence of the $n$- and $l$-level populations is investigated. The $K$-shell x-ray emission cross sections are determined by using the calculated state-selective electron capture results as input and then applying hydrogenic branching and cascading values for the photon emission. Our results compare favorably with experimental data from the KVI-Groningen, Jet Propulsion Laboratory and Lawrence Livermore National Laboratory groups.

We report an experimental demonstration of Raman self-focusing and self-defocusing in a far-off resonant alkali-metal atomic system. The key idea is to drive a hyperfine transition in an alkali-metal atom to a maximally coherent state with two laser beams. In this regime, the two-photon detuning from the Raman resonance controls the nonlinear index of the medium.

We investigate time-dependent properties of Einstein-Podolsky-Rosen (EPR) light beams generated in a nondegenerate optical parametric oscillator (NOPO) driven by a sequence of laser pulses with Gaussian time-dependent envelopes. This investigation continues our previous analysis [H. H. Adamyan and G. Yu. Kryuchkyan, Phys. Rev. A 74, 023810 (2006)] and involves problems of two-mode quadrature squeezing as well as intensity-difference squeezing in the time domain. The peculiarities of EPR beams are also discussed in the framework of phase-space quantum distributions. Two kinds of non-Gaussian Wigner functions, for the reduced one-mode state of periodically pulsed NOPO and for EPR beams which are combined on a one-half beam splitter are calculated numerically. We also investigate the Wigner functions of intensity-correlated twin beams following the conditional photon state-preparation scheme. It is demonstrated that the Wigner functions involve negative values in parts of the phase space for the schemes with one, two, and three photons.

We examine theoretically and experimentally an imaging scheme that uses the transverse intensity profile of the scattered light to reconstruct the locations of absorbers embedded in a turbid medium. This method is based on an a priori knowledge of the scattered light patterns associated with a single absorber that is located at various positions inside the medium. We discuss the range of validity of this method, and its sensitivity with regard to noise, and propose an algorithm to improve its accuracy.

We investigate the conditions for and properties of the complete tunneling of light through a composite barrier made of impedance-mismatched metamaterial layers. It is shown that two kinds of complete tunneling phenomena exist: phase-unmodulated and phase-modulated complete tunneling. The local surface modes formed near the interfaces between the metamaterial barrier layers play key roles in complete tunneling. Using the terminology of coupled-mode theory, phase-unmodulated complete tunneling occurs through successive mode couplings: from the incident light to the local surface mode and then to the other local surface mode and finally to the light mode in the transmission layer. Phase-modulated complete tunneling results from the complete transfer of the incident optical power to the transmission layer through the direct mediation of the symmetrically and antisymmetrically coupled supermodes of the local surface modes.