We demonstrate experimentally the guiding of cold and slow ND${}_3$ molecules along a thin charged wire over a distance of $\sim 0.34$ m through an entire molecular beam apparatus. Trajectory simulations confirm that both linear and quadratic high-field-seeking Stark states can be efficiently guided from the beam source up to the detector. A density enhancement up to a factor 7 is reached for beams with velocities ranging down to $\sim 150$m/s generated by the rotating nozzle technique.

We consider Bloch oscillations of Bose-Einstein condensates in the presence of a time-modulated $s$-wave scattering length. Generically, the interaction leads to dephasing and decay of the wave packet. Based on a cyclic-time argument, we find—in addition to the linear Bloch oscillation and a rigid soliton solution—an infinite family of modulations that lead to a periodic time evolution of the wave packet. In order to quantitatively describe the dynamics of Bloch oscillations in the presence of time-modulated interactions, we employ two complementary methods: collective coordinates and the linear stability analysis of an extended wave packet. We provide instructive examples and address the question of robustness against external perturbations.

A gain-assisted model is considered to study the Goos-H$\ddot{\text{a}}$nchen (GH) shift behavior in the reflected and transmitted light. In this model, a probe light is incident on a cavity containing three-level dilute gaseous atomic medium. The atom-field interaction follows two-photon Raman transitions, and the dielectric susceptibility of the medium exhibits dispersion and gain properties [L. J. Wang, A. Kuzmich, and A. Dogariu, Nature (London) 406, 227 (2000)]. Under appropriate conditions, two gain peaks are observed with anomalous dispersion between the peaks, whereas normal dispersion can be observed at and around the gain maxima. The manipulation of the detuning associated with the probe light field which interacts with the intracavity medium during its propagation through the cavity can lead to a control over negative and positive GH shift in the reflected and transmitted light beam via the anomalous and normal dispersion of the medium.

The dynamics of Glauber-Fock lattice of size $N$ is given through exact diagonalization of the corresponding Hamiltonian; the spectra $\left\{{\lambda }_k\right\}$ is given as the roots of the $N$th Hermite polynomial, $H_N({\lambda }_k/\sqrt{2})=0$, and the eigenstates are given in terms of Hermite polynomials evaluated at these roots. The exact dynamics is used to study coherent phenomena in discrete lattices. Due to the symmetry and spacing of the eigenvalues $\left\{{\lambda }_k\right\}$, oscillatory behavior is predicted with highly localized spectra, that is, near complete revivals of the photon number and partial recovery of the initial state at given waveguides.

We study the theory of degenerate three-wave mixing and the generation of squeezed microwaves using circuit quantum electrodynamics in solid state circuits. The Hamiltonian for degenerate three-wave mixing, which seemed to be given phenomenologically in quantum optics, is derived by quantum mechanical calculations. The nonlinear medium needed in three-wave mixing is composed of a series of superconducting charge qubits which are located inside two superconducting transmission-line resonators. Here, the multiqubit ensemble is present to enhance the effective coupling constant between the two modes in the transmission-line resonators. In the squeezing process, the qubits are kept in their ground states so that their decoherence does not corrupt the squeezing. The main obstacle preventing a large squeezing efficiency is the decay rate of the transmission-line resonator.

We explore the coherent destruction of tunneling (CDT) in a lattice array under selective in-phase harmonic modulations, in which some selected lattice sites are driven by in-phase harmonic oscillating fields and other lattice sites are undriven. Due to the occurrence of CDT, if the driving amplitude $A$ and the driving frequency $\omega$ are tuned to satisfy the zeroth-order Bessel function $J_0(A/\omega )=0$, the driven lattice sites are approximately decoupled from the undriven lattice sites. The CDT even takes place in lattice systems with high-order couplings between non-nearest-neighbor lattice sites. By using the CDT induced by selective in-phase harmonic modulations, we propose a scheme for realizing directed transport of a single particle. It is possible to observe the CDT in an engineered optical waveguide array, which provides an opportunity for controlling light propagation and designing switchlike couplers.

We show that recent results on the interaction of causality-respecting particles with particles on closed timelike curves derived in [Phys. Rev. A 82, 062330 (2010)] depend on ambiguous assumptions about the form of the state which is inputted into the proposed equivalent circuit. Choosing a different form of this state leads to an opposite conclusion on the power of closed timelike curves.

We respond to the comment by Kłobus et al. [Phys. Rev. A 84, 056301 (2011)] by emphasizing that the equivalent circuit, once constructed, obeys the standard rules of quantum mechanics—hence there is no ambiguity in how to choose initial states in our model. We discuss the distinction between correlated ensembles produced nonlocally via measurements on entangled states and those produced via local preparation.

Ultracold atoms in specifically designed optical lattices can be used to mimic the many-particle Hamiltonian (whose effective parameters can be tuned in a wide range) describing electrons and positrons in an external electric field. This analogy facilitates the experimental simulation of (so far unobserved) fundamental quantum phenomena such as the Schwinger effect, i.e., spontaneous electron-positron pair creation out of the vacuum by a strong electric field. Such an experiment would also test nonperturbative aspects of these lattice systems.

A translation operator is introduced to describe the quantum dynamics of a position-dependent mass particle in a null or constant potential. From this operator, we obtain a generalized form of the momentum operator as well as a unique commutation relation for $\widehat{x}$ and ${\widehat{p}}_{\gamma }$. Such a formalism naturally leads to a Schrödinger-like equation that is reminiscent of wave equations typically used to model electrons with position-dependent (effective) masses propagating through abrupt interfaces in semiconductor heterostructures. The distinctive features of our approach are demonstrated through analytical solutions calculated for particles under null and constant potentials like infinite wells in one and two dimensions and potential barriers.

We propose a framework for calculating scattering and bound-state properties in anisotropic two-dimensional potentials. Using our method, we derive systematic approximations of partial wave phase shifts and binding energies. Moreover, the method is suitable for efficient numerical computations. We calculate the $s$-wave phase shift and binding energy of polar molecules in two layers polarized by an external field along an arbitrary direction. We find that scattering depends strongly on their polarization direction and that absolute interlayer binding energies are larger than thermal energies at typical ultracold temperatures.

We demonstrate that high-order-harmonic generation (HHG) spectroscopy can be used to probe stereoisomers of randomly oriented 1,2-dichloroethylene (C${}_2$H${}_2$Cl${}_2$) and 2-butene (C${}_4$H${}_8$). The high-harmonic spectra of these isomers are distinguishable over a range of laser intensities and wavelengths. Time-dependent numerical calculations of angle-dependent ionization yields for 1,2-dichloroethylene suggest that the harmonic spectra of molecular isomers reflect differences in their strong-field ionization. The subcycle ionization yields for the cis isomer are an order of magnitude higher than those for the trans isomer. The sensitivity in discrimination of the harmonic spectra of cis- and trans- isomers is greater than 8 and 5 for 1,2-dichloroethylene and 2-butene, respectively. We show that HHG spectroscopy cannot differentiate the harmonic spectra of the two enantiomers of the chiral molecule propylene oxide (C${}_3$H${}_6$O).

Energy-time entangled photon pairs remain tightly correlated in time when the photons are passed through equal magnitude, but opposite in sign, dispersion. A recent experimental demonstration has observed this effect on ultrafast time scales using second-harmonic generation of the photon pairs. However, the experimental signature of this effect does not require energy-time entanglement. Here, we demonstrate a direct analogue to this effect in narrow-band second-harmonic generation of a pair of classical laser pulses under similar conditions. Perfect cancellation is observed for fs pulses with dispersion as large as 850 fs${}^2$, comparable to the quantum result, but with an ${10}^{13}$-fold improvement in signal brightness.

In this paper, we provide a mechanism of decoherence suppression for open quantum systems in general and that for a “Schrödinger cat-like” state in particular, through strong couplings to non-Markovian reservoirs. Different from the usual strategies in the literature of suppressing decoherence by decoupling the system from the environment, here the decoherence suppression employs a strong back-reaction from non-Markovian reservoirs. The mechanism relies on the existence of the singularities (bound states) of the nonequilibrium retarded Green function, which completely determines the dissipation and decoherence dynamics of open systems. As an application, we examine the decoherence dynamics of a photonic crystal nanocavity that is coupled to a waveguide. The strong non-Markovian suppression of decoherence for the “optical cat” state is attained.

The entanglement properties of a two-qubit system are analyzed from the point of view of Lie algebras and geometry. We deal with $4\times 4$ matrices belonging to a particular class having seven free parameters, constructed from the imposed symmetries on two-qubit states expanded in terms of a basis whose elements belong to a subalgebra of su(4). The entanglement or separability character of the state is determined and measured by analyzing the eigenvalues of an auxiliary matrix obtained from the original state after performing on it a nonunitary operation. In terms of its eigenvalues, we define two squared distances having a Minkowski metric, $s^2=t^2-{\vec{V}}^2$, which become a measure of the entanglement. The Minkowski metric is a signature of that class of two-qubit states (matrices) and also of the auxiliary matrices to be constructed. The squared distance is invariant by any unitary transformation on the two-qubit state. We illustrate the theory with examples.

We develop a rather general approach to entanglement characterization based on convexity properties and polynomial identities. This approach is applied to obtain simple and efficient entanglement conditions that work equally well in both discrete as well as continuous-variable environments. Examples of violations of our conditions are presented.

We present a theoretical study of the isotope effect arising from the replacement of H by T in the charge-transfer collision H($n=2$) + He${}^{+}\left(1s\right)$ at low energy. Using a quasimolecular approach and a time-dependent wave-packet method, we compute the cross sections for the reaction including the effects of the nonadiabatic radial and rotational couplings. For H($2s$) + He${}^{+}\left(1s\right)$ collisions, we find a strong isotope effect at energies below 1 eV/amu for both singlet and triplet states. We find a much smaller isotopic dependence of the cross section for H($2p$) + He${}^{+}\left(1s\right)$ collisions in triplet states, and no isotope effect in singlet states. We explain the isotope effect on the basis of the potential energy curves and the nonadiabatic couplings, and we evaluate the importance of the isotope effect on the charge-transfer rate coefficients.

We model electric field noise from fluctuating patch potentials on conducting surfaces by taking into account the finite geometry of the ion trap electrodes to gain insight into the origin of anomalous heating in ion traps. The scaling of anomalous heating rates with surface distance $d$ is obtained for several generic geometries of relevance to current ion trap designs, ranging from planar to spheroidal electrodes. The influence of patch size is studied both by solving Laplace's equation in terms of the appropriate Green's function as well as through an eigenfunction expansion. Scaling with surface distance is found to be highly dependent on the choice of geometry and the relative scale between the spatial extent of the electrode, the ion-electrode distance, and the patch size. Our model generally supports the $d^{-4}$ dependence currently found by most experiments and models, but also predicts geometry-driven deviations from this trend.

Laser orientation in the initial state has been used to study the properties of satellite transitions in inner-shell photoionization of rubidium atoms. The linear magnetic dichroism in the angular distribution (LMDAD) has been utilized to probe the continuum waves of orbital angular momentum conserving monopole, and angular momentum changing conjugate satellites, accompanying the $4p$ ionization of atomic Rb. We show experimentally that LMDAD of both types of satellite transitions is nonzero and that LMDAD of monopole satellites, measured as a function of photon energy, mimics the LMDAD of direct photoionization, whereas the LMDAD of conjugate transitions deviates drastically from that trend. The results indicate that conjugate transitions cannot be described theoretically without explicit inclusion of electron-electron interaction. The present data can thus be used as a very precise test of current models for photoionization.

Photoelectron holography is studied experimentally and computationally using the ionization of ground-state xenon atoms by intense near-infrared radiation. A strong dependence of the occurrence of the holographic pattern on the laser wavelength and intensity is observed, and it is shown that the observation of the hologram requires that the ponderomotive energy $U_p$ is substantially larger than the photon energy. The holographic interference is therefore favored by longer wavelengths and higher laser intensities. Our results indicate that the tunneling regime is not a necessary condition for the observation of the holographic pattern, which can be observed under the conditions formally attributed to the multiphoton regime.