We study the temporal and spatial dynamics of two light pulses, a probe and a switch, propagating through an asymmetric double quantum well where tunneling-induced quantum interference may be observed. When such an interference takes place, in the absence of the switch, the quantum well is transparent to the probe which propagates over sufficiently long distances at very small group velocities. In the presence of a relatively strong switch, however, the probe pulse is absorbed due to the quenching of tunneling-induced quantum interference. The probe may be made to vanish even when switch and probe are somewhat delayed with respect to one another. Conversely, our asymmetric double quantum well may be rendered either opaque or transparent to the switch pulse. Such a probe-switch “reciprocity” can be used to devise a versatile all-optical quantum interference-based solid-state switch for optical communication devices.

We propose a simple scheme for the generation of four-photon polarization-entangled decoherence-free states by using a pair of spontaneous parametric down-conversions and one tunable beam splitter. The scheme is based on post-selection strategy and feasible by current experimental technology.

We analyze the entanglement generation in a one-dimensional scattering process. The two colliding particles have a Gaussian wave function and interact by hard-core repulsion. In our analysis, results on the entanglement of two-mode Gaussian states are used. The produced entanglement depends in a nonobvious way on the ratio of masses and initial widths for the two particles. The asymptotic wave function of the two particles and its associated ellipse yield additional geometric insight into these conditions. We discuss the difference from the quantitative analysis of the amount of entanglement generated by beam splitters with squeezed light.

We have used an electron beam ion trap to observe a visible line at that corresponds to the magnetic dipole transition within the ground state configuration of . We have found no evidence to support the claim by others that a line near this position originates from . The comparison of the measured wavelength with previous indirect experimental values, and the dependence of the line intensity on the electron beam energy, confirms the validity of the present identification. Our measured wavelength is in agreement with semiempirical Hartree-Fock calculations but shows a discrepancy with multiconfiguration Dirac-Fock calculations. We propose that the line may be useful as a diagnostic for extreme ultraviolet lithography light sources.

Bound states and collisions of atoms with two-channel two-body interactions in harmonic waveguides are analyzed. The closed-channel contributions to two-atom bound states become dominant in the case of a weak resonance. At low energies and values of the nonresonant scattering length the problem can be approximated by a one-dimensional resonant model. The three-body problem becomes nonintegrable and the properties of triatomic molecules become different from those predicted by the integrable Lieb-Liniger-McGuire model.

We show how long-lived self-localized matter waves can exist in Bose-Einstein condensates with a nonlinear dissipative mechanism. The ingredients leading to such structures are a spatial phase generating a flux of atoms toward the condensate center and the dissipative mechanism provided by the inelastic three-body collisions in atomic Bose-Einstein condensates. The outcome is a striking example of nonlinear structure supported by dissipation.

We suggest a technique for the observation of a predicted supersolid phase in extended Bose–Hubbard models which are potentially realizable in cold-atom optical lattice systems. In particular, we discuss important subtleties arising from the existence of the trapping potential which lead to an externally imposed (as opposed to spontaneous) breaking of translational invariance. We show, by carefully including the trapping potential in our theoretical formalism, that noise correlations could prove instrumental in identifying the supersolid and density wave phases. We also find that the noise correlation peak width scales inversely with the relative size of trapped Mott domains.

We consider $n$ identically prepared qubits and study the asymptotic properties of the joint state ${\rho }^{\otimes n}$. We show that for all individual states, $\rho$ situated in a local neighborhood of size $1∕\sqrt{n}$ of a fixed state ${\rho }^{\mathbf{0}}$, the joint state converges to a displaced thermal equilibrium state of a quantum harmonic oscillator. The precise meaning of the convergence is that there exists physical transformations $T_n$ (trace preserving quantum channels) which map the qubits states asymptotically close to their corresponding oscillator state, uniformly over all states in the local neighborhood. A few consequences of the main result are derived. We show that the optimal joint measurement in the Bayesian setup is also optimal within the point-wise approach. Moreover, this measurement converges to the heterodyne measurement which is the optimal joint measurement of position and momentum for the quantum oscillator. A problem of local state discrimination is solved using local asymptotic normality.

The ion phase-space dynamics in the Coulomb explosion of very large ($\sim {10}^6–{10}^7$ atoms) deuterium clusters can be tailored using two consecutive laser pulses with different intensities and an appropriate time delay. For suitable sets of laser parameters (intensities and delay), large-scale shock shells form during the explosion, thus highly increasing the probability of fusion reactions within the single exploding clusters. In order to analyze the ion dynamics and evaluate the intracluster reaction rate, a one-dimensional theory is used, which approximately accounts for the electron expulsion from the clusters. It is found that, for very large clusters (initial radius $\sim 100\mathrm{nm}$), and optimal laser parameters, the intracluster fusion yield becomes comparable to the intercluster fusion yield. The validity of the results is confirmed with three-dimensional particle-in-cell simulations.

Recent work investigating resonant nonlinear magneto-optical rotation (NMOR) related to long-lived $({\tau }_{\mathrm{rel}}\sim 1\mathrm{s})$ ground-state atomic coherences has demonstrated potential magnetometric sensitivities exceeding ${10}^{-11}\mathrm{G}∕\sqrt{\mathrm{Hz}}$ for small $(\lesssim 1\mathrm{\mu }\mathrm{G}$) magnetic fields. In the present work, NMOR using frequency-modulated light (FM NMOR) is studied in the regime where the longitudinal magnetic field is in the geophysical range$(\sim 500\mathrm{mG})$, of particular interest for many applications. In this regime a splitting of the FM NMOR resonance due to the nonlinear Zeeman effect is observed. At sufficiently high light intensities, there is also a splitting of the FM NMOR resonances due to ac Stark shifts induced by the optical field, as well as evidence of alignment-to-orientation conversion type processes. The consequences of these effects for FM-NMOR-based atomic magnetometry in the geophysical field range are considered.

We consider a system of $N$ two-level atoms (spins) interacting with the radiation field in a dispersive but high-$Q$ cavity. Under an adiabatic condition, the interaction Hamiltonian reduces to a function of spin operators which is capable of producing spin squeezing. For a bipartite system $(N=2)$, the expressions for spin squeezing get very simple, giving a clear indication of close to 100% noise reduction. We analyse this squeezing as a measure of bipartite entanglement.

We investigate entanglement between collective operators of two blocks of oscillators in an infinite linear harmonic chain. These operators are defined as averages over local operators (individual oscillators) in the blocks. On the one hand, this approach of “physical blocks” meets realistic experimental conditions, where measurement apparatuses do not interact with single oscillators but rather with a whole bunch of them, i.e., where in contrast to usually studied “mathematical blocks” not every possible measurement is allowed. On the other, this formalism naturally allows the generalization to blocks which may consist of several noncontiguous regions. We quantify entanglement between the collective operators by a measure based on the Peres-Horodecki criterion and show how it can be extracted and transferred to two qubits. Entanglement between two blocks is found even in the case where none of the oscillators from one block is entangled with an oscillator from the other, showing genuine bipartite entanglement between collective operators. Allowing the blocks to consist of a periodic sequence of subblocks, we verify that entanglement scales at most with the total boundary region. We also apply the approach of collective operators to scalar quantum field theory.

We perform the quantitative evaluation of the entanglement dynamics in scattering events between two indistinguishable electrons interacting via the Coulomb potential in one- and two-dimensional semiconductor nanostructures. We apply a criterion based on the von Neumann entropy and the Schmidt decomposition of the global state vector suitable for systems of identical particles. From the time-dependent numerical solution of the two-particle wave function of the scattering carriers we compute their entanglement evolution for different spin configurations: two electrons with the same spin, with different spin, and singlet and triplet spin states. The procedure allows us to evaluate the mechanisms that govern entanglement creation and their connection with the characteristic physical parameters and initial conditions of the system. The cases in which the evolution of entanglement is similar to the one obtained for distinguishable particles are discussed.

The Dirac $R$-matrix method is used for solving the relativistic close-coupling equations for the electron impact excitation of $\mathrm{Ni}\mathrm{XIX}$. Target states up to the principal quantum number $n=5$ are included in the calculation. Highly accurate results are obtained in our calculations with the inclusion of resonance effects, channel coupling effects, and fully relativistic effects. We demonstrate that strong resonances appear in the excitation of the highly-charged ion $\mathrm{Ni}\mathrm{XIX}$, in particular for intercombination and forbidden transitions. Large differences are found when compared with previous calculations carried out with the distorted wave method. This calculation has direct applications to laboratory measurements and observations of astrophysical x-ray sources.

Some nonclassical properties of a particular state of light are demonstrated by computing the Wigner function. A quantum model of generating this state is proposed. A criterion called the distance variation difference is introduced to measure how far any state is from its corresponding coherent state.

This work investigates how a conical singularity can affect the specific heat of systems. A free nonrelativistic particle confined to the lateral surface of a cone—conical box—is taken as a toy model. Its specific heat is determined as a function of the deficit angle and the temperature. For a vanishing deficit angle, the specific heat is that of a particle in a flat disk where a characteristic temperature separates quantum and classical behaviors, as usual. By increasing the deficit angle the characteristic temperature also increases, and eventually another characteristic temperature (which does not depend on the deficit angle) arises. When the cone gets sufficiently sharp, at low and intermediate temperatures the azimuthal degree of freedom is suppressed. At low temperatures the specific heat varies discontinuously with the deficit angle. Connections between certain theorems regarding common zeros of the Bessel functions and this discontinuity are reported.

Quantum tunneling across a static potential barrier in a static magnetic field is very sensitive to an analytical form of the potential barrier. Depending on that, the oscillatory structure of the modulus of the wave function can be formed in the direction of tunneling. Due to an underbarrier interference, the probability of tunneling through a higher barrier can be larger than through a lower one. For some barriers the quantum interference of underbarrier cyclotron paths results in a strong enhancement of tunneling. This occurs in the vicinity of the certain magnetic field and is referred to as Euclidean resonance. This strongly contrasts to the Wentzel, Kramers, and Brillouin type tunneling which occurs with no magnetic field.

We propose a range criterion that is a sufficient and necessary condition satisfied by two pure states transformable into each other under reversible stochastic local operations assisted by classical communication. We also provide a systematic method for seeking all kinds of true entangled states in the $2\times M\times N$ system, and can effectively distinguish them by means of the range criterion. The efficiency of the criterion and the method is exhibited by the classification of true entanglement in some types of tripartite systems.