A nonperturbative treatment is presented for laser-pulse-driven formation of heteronuclear diatomic molecules in a thermal gas of atoms. Based on the assumption of full controllability, the maximum possible photoassociation yield is obtained. A one-dimensional model is used for calculating the photoassociation probability as a function of the laser parameters as well as for different temperatures. The dependence of the photoassociation yield on the laser frequency and amplitude reveals complex patterns of one- and multiphoton transitions. The photoassociation yield induced by subpicosecond pulses of a priori fixed shape is very low compared to the maximum possible yield.

The time-dependent effective-range (TDER) theory introduced by Frolov et al. [Phys. Rev. Lett. 91, 053003 (2003)] and used in numerous applications for processes involving a linearly polarized intense laser field is presented in detail for the general problem of an electron, initially bound in a short-range potential, interacting with a laser field of arbitrary polarization. The TDER theory combines the well-known effective-range theory for a weakly bound electron in a short-range potential with the quasistationary, quasienergy state (QQES) or Floquet formulation for an electron interacting with a harmonic, time-dependent field, such as a monochromatic laser field. We present the basic underlying assumptions, the relevant boundary conditions, and the key equations for both the quasienergy $ϵ$ of the system and its associated, three-dimensional, time-dependent wave function ${\Phi }_{ϵ}(\mathbf{r},t)$. The specific equations appropriate for two initial state symmetries (i.e., $s$- or $p$-valence electrons) and for three cases of laser field polarization (linear, circular, and elliptical) are derived and discussed. Results of the formulation are presented for the specific case of the Stark shift (and level splitting, in the case of an initially degenerate $p$ state) and detachment rates for ${\mathrm{H}}^{-}$, ${\mathrm{O}}^{-}$, the negative alkali-metal ions, and the negative halogen ions.

Enhanced ionization of $\mathrm{H}_2{}^{+}$ in intense ultrashort laser pulses was measured using molecular dissociation imaging of an $\mathrm{H}_2{}^{+}$ beam and with a pump-probe technique using cold target recoil ion momentum spectroscopy on a ${\mathrm{D}}_2$ target. Both measurements show a broad, single-peak distribution for enhanced ionization, in contrast to the double-peak structure predicted by “frozen” nuclei theory. This calculated double-peak structure is most likely washed out by nuclear motion and to a lesser extent by intensity averaging.

We introduce a measure to quantify the non-Gaussian character of a quantum state: the quantum relative entropy between the state under examination and a reference Gaussian state. We analyze in detail the properties of our measure and illustrate its relationships with relevant quantities in quantum information such as the Holevo bound and the conditional entropy; in particular, a necessary condition for the Gaussian character of a quantum channel is also derived. The evolution of non-Gaussianity is analyzed for quantum states undergoing conditional Gaussification toward twin beams and de-Gaussification driven by Kerr interaction. Our analysis allows us to assess non-Gaussianity as a resource for quantum information and, in turn, to evaluate the performance of Gaussification and de-Gaussification protocols.

We provide evidence for the dipole blockade of Rydberg excitation by examining the distributions of the number of Rydberg excitations created in ensembles of interacting Rydberg atoms. We show that, over a range of densities, the Rydberg excitation number distributions become significantly narrower when an applied electric field is used to tune the ${}^{85}\mathrm{Rb}$ interaction channel $45D_{5∕2}+45D_{5∕2}\to 43F+47P_{3∕2}$ into Förster resonance. Substantially sub-Poissonian distributions that agree with published theory were achieved using very dense atom samples tuned into Förster resonance.

Ghost-imaging experiments correlate the outputs from two photodetectors: a high spatial-resolution (scanning pinhole or charge-coupled-device camera) detector that measures a field which has not interacted with the object to be imaged and a bucket (single-pixel) detector that collects a field that has interacted with the object. We describe a computational ghost-imaging arrangement that uses only a single-pixel detector. This configuration affords background-free imagery in the narrow-band limit and a three-dimensional sectioning capability. It clearly indicates the classical nature of ghost-image formation.

A simple relation is introduced for concurrence to describe how much the entanglement of a bipartite system is at least left if either (or both) subsystem undergoes an arbitrary physical process. This provides a lower bound for concurrence of mixed states (pure states are included) in contrast to the upper bound given by Konrad et al. [Nat. Phys. 4, 99 (2008)]. Our results are also suitable for general high-dimensional bipartite quantum systems.

Atomic systems in regular lattices are intriguing systems for implementing ideas in quantum simulation and information processing. Focusing on laser-cooled ions forming Wigner crystals in Penning traps, we find a robust and simple approach to engineering nontrivial two-body interactions sufficient for universal quantum computation. We then consider extensions of our approach to the fast generation of large cluster states and a nonlocal architecture using an asymmetric entanglement generation procedure between a Penning trap system and well-established linear Paul trap designs.

In this paper we provide the analytical derivation of the global geometric entanglement per block for the valence-bond solid ground state of the spin-1 Affleck-Kennedy-Lieb-Tasaki chain. In particular, we show that this quantity saturates exponentially fast to a constant when the sizes of the blocks are sufficiently large. Our result provides an example of an analytical calculation of the geometric entanglement for a gapped quantum many-body system in one dimension and far away from a quantum critical point.

We provide various schemes for the splitting up of quantum information into parts using four- and five-partite cluster states. Explicit protocols for the quantum information splitting (QIS) of single- and two-qubit states are illustrated. It is found that the four-partite cluster state can be used for QIS of an entangled state and the five-partite cluster state can be used for QIS of an arbitrary two-qubit state. The schemes considered here are also secure against certain eavesdropping attacks.

We report the measurement of the diffusion coefficients of francium and rubidium ions implanted in a yttrium foil. We developed a methodology, based on laser spectroscopy, which can be applied to radioactive and stable species, and allows us to directly take record of the diffusion time. Francium isotopes are produced via fusion-evaporation nuclear reaction of a ${}^{18}\mathrm{O}$ beam on a Au target at the Tandem XTU accelerator facility in Legnaro, Italy. Francium is ionized at the gold-vacuum interface and ${\mathrm{Fr}}^{+}$ ions are then transported with an electrostatic beamline to a cell for neutralization and capture in a magneto-optical trap (MOT). A ${\mathrm{Rb}}^{+}$ beam is also available, which follows the same path as ${\mathrm{Fr}}^{+}$ ions. The accelerated ions are focused and implanted in an yttrium foil for neutralization. The time evolution of the MOT and the vapor fluorescence signals are used to determine diffusion times of Fr and Rb in Y as a function of temperature.

We consider laser alignment of ortho and para spin isomers of water molecules by using strong and short off-resonance laser pulses. A single pulse is found to create a distinct transient alignment and antialignment of the isomeric species. We suggest selective alignment of one isomeric species (leaving the other species randomly aligned) by a pair of two laser pulses.

We apply the atom counting theory to strongly correlated Fermi systems and spin models, which can be realized with ultracold atoms. The counting distributions are typically sub-Poissonian and remain smooth at quantum phase transitions, but their moments exhibit critical behavior, and characterize quantum statistical properties of the system. Moreover, more detailed characterizations are obtained with experimentally feasible spatially resolved counting distributions.

We calculate the effect of quantum noise in supersonic transport of Bose-Einstein condensates. When an obstacle obstructs the flow of atoms, quantum fluctuations cause atoms to be scattered incoherently into random directions. This suppresses the propagation of Cherenkov radiation, creating quantum turbulence and a crescent of incoherent atoms around the obstacle. We observe similar dynamics if the BEC is stirred by a laser beam: crescents of incoherent atoms are emitted from the laser’s turning points. Finally, we investigate supersonic flow through a disordered potential, and find that the quantum fluctuations generate an accumulation of incoherent atoms as the condensate enters the disorder.

Ultracold Rb atoms were used to demonstrate nondegenerate four-wave mixing through a Rydberg state. Continuous $5S\text{−}5P\text{−}nD$ two-photon excitation to the Rydberg state was combined with an $nD\text{−}6P$ tuned laser in a phase-matched geometry. The angular dependence, spatial profile, and dependence on detuning were investigated, showing good agreement with theory. Under optimum conditions 50% of the radiation was emitted into the phase-matched direction. The directional emission is promising for studying quantum effects in blockaded atom clouds.

A representation theory of finite electromagnetic beams in free space is formulated by factorizing the field vector of the plane-wave component into a $3\times 2$ mapping matrix and a two-component Jones-like vector. The mapping matrix has one degree of freedom that can be described by the azimuthal angle of a fixed unit vector with respect to the wave vector. This degree of freedom allows us to find out such a beam solution in which every plane-wave component is specified by the same fixed unit vector $\mathbf{I}$ and has the same normalized Jones-like vector. The angle ${\theta }_I$ between the fixed unit vector $\mathbf{I}$ and the propagation axis acts as a parameter that describes the vectorial property of the beam. The impact of ${\theta }_I$ is investigated on a beam of angular-spectrum field scalar that is independent of the azimuthal angle. The field vector in position space is calculated in the first-order approximation under the paraxial condition. A transverse effect is found that a beam of elliptically polarized angular spectrum is displaced from the center in the direction that is perpendicular to the plane formed by the fixed unit vector and the propagation axis. The expression of the transverse displacement is obtained. Its paraxial approximation is also given.

We investigate the time taken for global collapse by a dipolar Bose-Einstein condensate. Two semianalytical approaches and exact numerical integration of the mean-field dynamics are considered. The semianalytical approaches are based on a Gaussian ansatz and a Thomas-Fermi solution for the shape of the condensate. The regimes of validity for these two approaches are determined, and their predictions for the collapse time revealed and compared with numerical simulations. The dipolar interactions introduce anisotropy into the collapse dynamics and predominantly lead to collapse in the plane perpendicular to the axis of polarization.

The quantized surface mode technique is used to calculate the Casimir force between two parallel anisotropic metamaterial plates with in-plan optical axes, and the main concern is focused on the possible attractive-repulsive transition of the force. The result shows that if the electric and magnetic responses of the plates are frequency dependent, the Casimir force between them is attractive when the separation is small and is able to become repulsive as the separation increases. Moreover, the polarity of the Casimir force depends on the degree of anisotropy near the zero-force position.

We study the scaling of the convergence of several statistical properties of a recently introduced random unitary circuit ensemble towards their limits given by the circular unitary ensemble. Our study includes the full distribution of the absolute square of a matrix element, moments of that distribution up to order eight, as well as correlators containing up to 16 matrix elements in a given column of the unitary matrices. Our numerical scaling analysis shows that all of these quantities can be reproduced efficiently, with a number of random gates which scales at most as $n_q{\left[\ln (n_q∕ϵ)\right]}^{\nu }$ with the number of qubits $n_q$ for a given fixed precision $ϵ$ and $\nu >0$.

We operated a high-current, wall-stabilized arc in a gaseous mixture containing chlorine and observed $4s\text{−}4p$, $4p\text{−}4d$, and $4p\text{−}5d$ transitions in the red and near infrared spectrum. We measured their relative transition probabilities end-on and put them on an absolute scale with a lifetime value obtained from the literature. We achieved good agreement with recent sophisticated calculations and an earlier measurement for the stronger transitions, but encountered large differences for weak transitions.