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In quantum metrological applications based on ultracold atom systems, entangled initial states are thought necessary to achieve sub-shot-noise accuracies. This conclusion, although strictly true for systems of distinguishable particles, does no longer hold for systems of identical particles. Indeed, while quantum non-locality is necessary, it can be encoded into the interferometric apparatus and not into the initial states. In particular, no preliminary spin-squeezing is necessary to reach quantum performances in metrological applications of ultracold atom physics.

Fourier transform spectra are used to determine emission branching fractions for 1290 lines of the first spectrum of gadolinium (Gd i). These branching fractions are converted to absolute atomic transition probabilities using previously reported radiative lifetimes from time-resolved laser-induced-fluorescence measurements (Den Hartog et al2011 J. Phys. B: At. Mol. Opt. Phys.44 055001). The wavelength range of the data set is from 300 to 1850 nm. A least squares technique for separating blends of the first and second spectra lines is also described and demonstrated in this work.

Many-electron effects in the photoionization of Kr near the 3d⁹np resonances were investigated theoretically. Cross sections for the population of the 4p⁴(¹D)mp states, their alignment and orientation, and angular distribution of the Auger electrons were computed considering the resonance Auger effect as a coherent process. Probabilities of the radiative cascades following the resonant Auger effect were estimated quantitatively within the transition-array technique. The role of intra- and inter-shell correlations was investigated. Lineshapes computed, taking into account interchannel interaction, are in good agreement with the measured ones. Fourfold excitations of the Kr ground state were proposed to influence the resonance population, alignment and orientation of the 4p⁴np levels.

We study the dynamics of matter waves in an effectively one-dimensional Bose–Einstein condensate in a double-well potential. We consider in particular the case when one of the double wells confines excited states. Similar to the known ground state oscillations, the states can tunnel between the wells experiencing the physics known for electrons in a Josephson junction, or be self-trapped. As the existence of dark solitons in a harmonic trap is a continuation of such non-ground state excitations, one can view the Josephson-like oscillations as tunnellings of dark solitons. Numerical existence and stability analysis based on the full equation is performed, where it is shown that such tunnelling can be stable. Through a numerical path-following method, unstable tunnelling is also obtained in different parameter regions. A coupled-mode system is derived and compared to the numerical observations. Regions of (in)stability of Josephson tunnelling are discussed and highlighted. Finally, we outline an experimental scheme designed to explore such dark soliton dynamics in the laboratory.

We have studied the production of long-lived, highly excited, neutral hydrogen atom fragments following oxygen 1s inner-shell excitation/ionization of gas-phase water molecules using synchrotron radiation. Striking differences to fragment ion and low-n neutral H yields are observed close to threshold. To investigate the decay pathways involved, the neutral fragments were also detected in coincidence with H⁺, O^{2 +}, O⁺ and OH⁺ fragments.

We study the effects of a static electric field on the photoassociation of a heteronuclear atom pair into a polar molecule. The interaction of permanent dipole moment with a static electric field largely affects the ground state continuum wavefunction of the atom pair at short separations where photoassociation transitions occur according to the Franck–Condon principle. Electric field-induced anisotropic interaction between two heteronuclear ground state atoms leads to scattering resonances at some specific electric fields. Near such resonances the amplitude of the scattering wavefunction at short separation increases by several orders of magnitude. As a result, the photoassociation rate is enhanced by several orders of magnitude near the resonances. We discuss in detail electric field-modified atom–atom scattering properties and resonances. We calculate the photoassociation rate that shows giant enhancement due to electric field tunable anisotropic resonances. We present selected results among which particularly important are the excitations of higher rotational levels in ultracold photoassociation due to electric field tunable resonances.

We study the spectrum of density fluctuations in the ultra-cold gas of neutral atoms, confined in a magneto-optical trap. We determine the corresponding amplitude and spectra of laser light scattered by this medium. We derive an expression for the dynamical structure function, by using a test particle method. We propose to use the collective laser scattering as a diagnostic method for the microscopic properties of the ultra-cold matter. This will also allow us to check on the atomic correlations which are mediated by the collective mean field inside the gas.

As can be inferred from present experiments in ultracold gases, the scattering length is a quantity that determines the thermodynamic state of the gas. As such, a conjugate thermodynamic variable to it exists. Here, we show that the recently introduced contact is the conjugate of the inverse of the scattering length. We find that this identification, in addition to well-known approximations, allows for a derivation of three of the most relevant results concerning the contact, namely its relation to the adiabatic change of the energy, the general form of the energy and the generalized virial theorem. We find that the current identification of the contact variable depends on the use of the contact approximation for the intermolecular potential but it is independent of whether the gas is made out of fermions or bosons and of the strength of the interaction.

In this paper, we demonstrate that, by continuous single beam excitation, one can generate an abnormal anti-Stokes Raman emission (AASRE) whose properties are similar to a coherent anti-Stokes Raman scattering (CARS). The effect has been observed in materials which possess intrinsically nonlinear properties (LiNbO₃ and CdS), which have the electric susceptibility of third order different from zero, χ⁽³⁾ ≠ 0, as well as in materials that become nonlinear under resonant optical excitation. In the latter case, we used poly-3,4-ethylendioxythiophene (PEDOT) in its undoped state deposited electrochemically on Au support. Raman studies corroborated with images of optical microscopy demonstrate that the production of AASRE is conditioned by the existence of a particular morphology of the sample able to ensure efficient transport of the light inside the sample through a multiple light scattering mechanism. In this context, it was found that LiNbO₃ and CdS in powder form as well as the PEDOT films layered on a rough Au substrate are suitable morphological forms. We explain AASRE as resulting from a wave-mixing mechanism of the incident laser light ω_l with a Stokes-shifted Raman light ω_S produced by a spontaneous Raman light scattering process, both strongly scattered inside the sample. As a CARS process, AASRE is conditioned by the achievement of phase-matching requirements, which makes the difference between the wave vectors of mixing light close to zero, Δk =/2k_l − k_S − k_CARS/≈ 0. In condensed media, the small dispersion of the refractive index makes Δk ≈ 0 so that the formation of a favourable phase-matching geometry may be accomplished even at a crossing angle θ of travelling scattered light ω_l and ω_S. For tightly focused beams, the requirement of phase matching relaxes; it is no longer sensitive to the Raman shift, so that a wide intense anti-Stokes Raman spectrum is observed at an angle larger than the Stokes Raman spectrum.

The contribution of multiple forward scattering in Coulomb focusing of low-energy photoelectrons at above-threshold ionization in mid-infrared laser fields is investigated. It is shown that the high-order forward scattering can have a nonperturbative effect in Coulomb focusing. The effective number of rescattering events is defined and is shown to depend weakly on laser intensity and wavelength. Nevertheless, the relative contribution of forward scattering in Coulomb focusing and the Coulomb focusing in total decrease with increasing laser intensity and wavelength.

We investigate three-dimensional (3D) spatiotemporal vector solitary waves in spherical coordinates. The exact 3D analytical nonstationary (slowly expanding) solutions are obtained by the separation of variables and the Hirota bilinear method. Novel 3D spatiotemporal vector solitary waves are built with the help of spherical harmonics include multipole and necklace rings.

We propose several schemes for the joint remote preparation of four-qubit cluster-type states with real coefficients and complex coefficients by using six Einstein–Podolsky–Rosen (EPR) pairs and two six-qubit entangled states as quantum channels respectively. In these schemes, two senders share the original state which they wish to help the receiver to remotely prepare. It is shown that, only if two senders collaborate with each other, and perform four-qubit projective measurements on their own qubits respectively, the receiver can reconstruct the original state by means of some appropriate unitary operations.

We study quantum teleportation via two two-level atoms coupled collectively to a multimode vacuum field and prepared initially in different atomic states. We concentrated on the influence of the spontaneous emission, collective damping and dipole–dipole interaction of the atoms on fidelity dynamics of quantum teleportation and obtained the region of spatial distance between the two atoms over which the state can be teleported nonclassically. Moreover, we showed through concrete examples that entanglement of the channel state is the prerequisite but not the only essential quantity for predicting the teleportation fidelity.

A model is presented of nth order nonlinear processes in whispering gallery mode resonators, with scattering coherently coupling degenerate counter propagating modes. It is shown that such systems generate strong squeezing and time-delayed entanglement. The model can be generally applied to any pair of nonlinear coherently coupled cavities and is of particular relevance to whispering gallery mode resonators. A feature of the entanglement is that, by tuning the coherent coupling rate the peak entanglement can be tuned to occur away from the carrier frequency. This has technological significance allowing low frequency noise sources around the carrier frequency to be avoided. All-optical time-delayed entanglement has many applications, such as an all-optical quantum memory.

In this work, we study the dynamics of quantum correlation (QC) in terms of quantum discord and its transfer for multiqubit systems in dissipative environments. At first, we investigate the dynamics of bipartite QC contained in a three-qubit system that are initially prepared in an extended W-like state with each qubit coupled to an independent reservoir. Subsequently, we study a realistic quantum network of several remote nodes each of which contains two qubits in contact with a common reservoir. For the simplest case of two nodes, we study the dynamics of QC and its transfer from the initially correlated system to the reservoirs and other degrees of freedom. In both models, we pay particular attention to the independent evolution and transfer of QC without the participation of entanglement when the systems of interest are initially prepared in unentangled states. We also observe the occurrence of sudden changes of quantum discord when the systems are initially in mixed states.

We calculate high-harmonic generation (HHG) by intense infrared lasers in atoms and molecules with the inclusion of macroscopic propagation of the harmonics in the gas medium. We show that the observed experimental spectra can be accurately reproduced theoretically despite the sensitivities of the HHG spectra to the experimental conditions. We further demonstrate that the simulated (or experimental) HHG spectra can be factored out as a product of a 'macroscopic wave packet' and the photo-recombination transition dipole moment where the former depends on the laser properties and the experimental conditions, while the latter is the property of the target only. The factorization makes it possible to extract target structure from experimental HHG spectra, and for ultrafast dynamic imaging of transient molecules.

We investigate the generation of even and odd harmonics using an intense laser and a weak second harmonic field. Our theoretical approach is based on solving the saddle-point equations within the strong field approximation. The phase of the even harmonic oscillation as a function of the delay between the fundamental and second harmonic field is calculated and its variation with energy is found to be in good agreement with recent experimental results. We also find that the relationship between this phase variation and the group delay of the attosecond pulses depends on the intensity and wavelength of the fundamental field as well as the ionization potential of the atom.