Considering the photoionization of $\mathrm{Ar}@{\mathrm{C}}_{60}$, we predict resonant femtosecond decays of both Ar and ${\mathrm{C}}_{60}$ vacancies through the continua of atom-fullerene hybrid final states. For Ar $3s\to np$ excitations, these resonances are far stronger than the Ar-to-${\mathrm{C}}_{60}$ resonant intersite-Coulombic decays (ICD), while for ${\mathrm{C}}_{60}$ excitations they are strikingly larger than the corresponding Auger features. The results indicate the power of hybridization to enhance decay rates and modify lifetimes and line profiles, offering a unique probe, more powerful than regular ICDs, for multicenter decay processes.

Photoemission from diatomic molecules closely resembles the Young-type double-slit experiment where each of the two atomic sites represents a coherent emission source. When the photoelectron wavelength becomes commensurate with the effective interatomic distance, the resulting spatial interference gives rise to oscillations in the photoionization total and differential cross sections. This phenomenon provides detailed information on the molecular geometry, a fact that can be utilized for probing the nuclear dynamics triggered by the interaction with a laser field. We demonstrate how this coherent wave-packet evolution can be traced by observing the photoelectron angular distribution. Based on ab initio scattering calculations we perform a proof-of-principle reconstruction of the nuclear-wave-packet evolution in the $\mathrm{He}{\mathrm{H}}^{2+}$ molecule.

We present a highly efficient technique for observing an avoided-crossing signal resulting from modified decay branching ratios of excited atomic states in the vicinity of avoided crossings (ACs) formed in tunable external fields. The technique is based on detection of atoms in metastable (MS) states, and we apply it to the case of photoexcited helium atoms which cascade to the singlet and triplet $1s2s$ states in a dc electric field. We show that narrow structures present in the MS atom yield are due to the increased probability to cascade to the triplet MS states at the field strengths at which the ACs emerge. The resolution of the present technique is not limited by the excitation bandwidth, only by the extent to which a homogeneous field can be produced over a limited region of space. Using results of high-precision calculations which include relativistic and QED corrections, we are able to reproduce the dependence of the measured MS atom yield on the electric-field strength.

We investigate few-photon extreme ultraviolet (XUV) double ionization of helium atoms without and in the presence of an assisting infrared (IR) laser field by numerically solving the time-dependent Schrödinger equation in full dimensionality within a finite-element discrete-variable-representation scheme. We discuss joint energy distributions for coplanar emission where the emitted electron momenta and polarization axis of the linearly polarized XUV and IR pulses lie in a plane. Our analysis focuses on joint angular distributions for highly correlated equal-energy-sharing double ionization by absorption of one, two, or three XUV photons and IR-laser-assisted single-photon XUV double ionization.

We consider the problem of formation of small-amplitude spatially localized oscillatory structures for atomic Bose-Einstein condensates confined in two- and three-dimensional optical lattices, respectively. Our approach is based on applying the regions with different signs of atomic effective masses where an atomic system exhibits effective hyperbolic dispersion within the first Brillouin zone. By using the $\mathbf{kp}$ method we have demonstrated mapping of the initial Gross-Pitaevskii equation on nonlinear Klein-Gordon and/or Ginzburg-Landau-Higgs equations, which is inherent in matter fields within ${\varphi }^4$-field theories. Formation of breatherlike oscillating localized states—atomic oscillons—as well as kink-shaped states have been predicted in this case. Apart from classical field theories atomic field oscillons occurring in finite lattice structures possess a critical number of particles for their formation. The obtained results pave the way to simulating some analogues of fundamental cosmological processes occurring during our Universe's evolution and to modeling nonlinear hyperbolic metamaterials with condensed matter (atomic) systems.

When a Bose-Einstein condensate is divided into two parts that are subsequently released and overlap, interference fringes are observed. We show here that this interference is typical, in the sense that most wave functions of the condensate, randomly sampled out of a suitable ensemble, display interference. We make no hypothesis of decoherence between the two parts of the condensate.

We propose and study a quantum pump which emulates a traditional paddlewheel, that can be implemented with ultracold atoms in waveguides. We use wave-packet propagation to study its single-mode dynamics, which also determines its multimode current for mesoscopic setups. Energy flow with or without particle transport is possible. The spectrum reveals unusual features such as nonuniform Floquet sidebands and counterintuitive scattering. Explanations are found by examining the scattering dynamics comparatively using quantum, classical, and semiclassical pictures, indicating a rich system and experimentally accessible method to explore quantum versus classical dynamics.

We investigate the large-time asymptotical behavior of a mobile impurity immersed in a degenerate Tonks-Girardeau gas. We derive a correct weak-coupling kinetic equation valid for N arbitrary ratio of masses of gas and impurity particles. When gas particles are either lighter or heavier than the impurity we find that our theory is equivalent to the Boltzmann theory with the collision integral calculated via the Fermi Golden Rule. On the contrary, in the equal-mass case, Fermi Golden Rule treatment gives false results due to not accounting for multiple coherent scattering events. The latter are treated by the resummation of ladder diagrams, which leads to a new kinetic equation. The asymptotic momentum of the impurity produced from this equation coincides with the result obtained by means of the Bethe ansatz.

We describe an experimental setup for imaging topologically protected Floquet edge states using ultracold bosons in an optical lattice. Our setup involves a deep two-dimensional optical lattice with a time-dependent superlattice that modulates the hopping between neighboring sites. The finite waist of the superlattice beam yields regions with different topological numbers. One can observe chiral edge states by imaging the real-space density of a bosonic packet launched from the boundary between two topologically distinct regions.

The major resolution-limiting factor in cryoelectron microscopy of unstained biological specimens is radiation damage by the very electrons that are used to probe the specimen structure. To address this problem, an electron microscopy scheme that employs quantum entanglement to enable phase measurement precision beyond the standard quantum limit has recently been proposed [H. Okamoto, Phys. Rev. A 85, 043810 (2012)]. Here we identify and examine in detail measurement errors that will arise in the scheme. Emphasis is given to considerations concerning inelastic scattering events because, in general, schemes assisted with quantum entanglement are known to be highly vulnerable to lossy processes. We find that the amount of error due to both elastic and inelastic scattering processes is acceptable provided that the electron beam geometry is properly designed and the specimen is sufficiently thin.

A strongly confined light field necessarily exhibits a local polarization that varies on a subwavelength scale. We demonstrate that a single optical mode of this kind can be used to selectively and simultaneously manipulate atomic ensembles that are less than a micron away from each other and equally coupled to the light field. The technique is implemented with an optical nanofiber that provides an evanescent field interface between a strongly guided optical mode and two diametric linear arrays of cesium atoms. Using this single optical mode, the two atomic ensembles can simultaneously be optically pumped to opposite Zeeman states. Moreover, the state-dependent light shifts can be made locally distinct, thereby enabling an independent coherent manipulation of the two ensembles. Our results open a route toward advanced manipulation of atomic samples in nanoscale quantum optics systems.

The effect of spatial correlations on the Purcell effect in a bidimensional dispersion of resonant nanoparticles is analyzed. We perform extensive calculations on the fluorescence decay rate of a point emitter embedded in a system of nanoparticles statistically distributed according to a simple two-dimensional lattice-gas model near the critical point. For short-range correlations (high temperature thermalization) the Purcell factors present a long-tailed statistic which evolves towards a bimodal distribution when approaching the critical point where the spatial correlation length diverges. Our results suggest long-range correlations as a possible origin of the large fluctuations of experimental decay rates in disordered metal films.

We study entanglement detection by using mutually unbiased measurements and provide a quantum separability criterion that can be experimentally implemented for arbitrary $d$-dimensional bipartite systems. We show that this criterion is more effective than the criterion based on mutually unbiased bases. For isotropic states our criterion becomes both necessary and sufficient.

Scattering properties of light in metamaterials are similar to those in open quantum systems. Here we propose an ultrathin tailored metamaterial designed to show that one-way zero reflection yielding to topologically stable phase dislocation is responsible for the exceptional point, one of the most important degeneracies in the non-Hermitian Hamiltonian. In order to bridge the exotic macroscopic optical phenomenon occurring in metamaterials, a phenomenological model under microscopic view is developed and good agreement with the full-blown numerical simulation is found. Our investigation uncovers the capabilities of metamaterials to exhibit extreme optical properties and to provide us with many potential applications such as the suppression of undesired scattering signals in the spectral band ranging from microwaves to visible light.

The nonequilibrium quantum dynamics of trapped bosons interacting by strong interparticle interaction of finite range in one, two, and three spatial dimensions is investigated on an accurate many-body level. We use different time-dependent processes to destabilize the systems' ground states: A sudden quench of the strength of the interparticle repulsion is accompanied by displacement of the trap. Two qualitatively different but otherwise generic dynamical quantum many-body behaviors are discovered. In the first, the overall “topology” of the ground-state density is preserved, whereas in the second the density totally “explodes.” An intuitive many-body time-dependent model is devised to interpret and explain the observations. The generality of the discovered scenarios is explicitly confirmed in traps of various shapes and dimensionality, and interparticle interactions of different forms and ranges. Implications are briefly discussed.

In this Rapid Communication we propose realistic schemes to realize topologically nontrivial Floquet states by shaking optical lattices, using both the one-dimensional lattice and two-dimensional honeycomb lattice as examples. The topological phase in the two-dimensional model exhibits quantum anomalous Hall effect. The transition between topological trivial and nontrivial states can be easily controlled by both shaking frequency and shaking amplitude. Our schemes have two major advantages. First, both the static Hamiltonian and the shaking scheme are sufficiently simple to implement. Secondly, it requires relatively small shaking amplitude and therefore heating can be minimized. These two advantages make our schemes much more practical.

We consider the resonant interaction energy and force between two identical atoms, one in an excited state and the other in the ground state, placed inside a photonic crystal. The atoms, having the same orientation as their dipole moment, are supposed prepared in their symmetrical state and interact with the quantum electromagnetic field. We consider two specific models of photonic crystals: a one-dimensional model and an isotropic model. We show that in both cases the resonant interatomic force can be strongly enhanced by the presence of the photonic crystal, as a consequence of the modified dispersion relation and density of states, in particular if the transition frequency of the atoms is close to the edge of a photonic gap. Differences between the two models of photonic crystal considered are discussed in detail, as well as a comparison with the analogous system of two impurity atoms in a quantum semiconductor wire. A numerical estimate of the effect in a realistic situation is also discussed.

The geometric phase is of fundamental interest and plays an important role in quantum information processing. However, the definition and calculation of this phase for open systems remain problematic due to the lack of agreement on generalizations of the parallel transport condition to mixed-state nonunity evolutions. Here we tackle this problem by associating the open-system geometric phase with the parallel transport of the joint system-reservoir state and find that the associated geometric phase can be calculated when the total Hamiltonian is time independent. Our approach not only provides a way around the nonunitary evolution obstacle, but also sheds light on the relation between the geometric phase and the system-reservoir entanglement. Based on this approach, we calculate the geometric phase of different quantum systems subject to energy decay, showing that it is robust against decoherence, which is in distinct contrast with previous results.

Atomic ions, confined in radio-frequency Paul ion traps, are a promising candidate to host a future quantum information processor. In this article, we demonstrate a method to couple two motional modes of a single trapped ion, where the coupling mechanism is based on applying electric fields rather than coupling the ion's motion to a light field. This reduces the design constraints on the experimental apparatus considerably. As an application of this mechanism, we cool a motional mode close to its ground state without accessing it optically. As a next step, we apply this technique to measure the mode's heating rate, a crucial parameter determining the trap quality.

We present a multichannel quantum-defect theory for magnetic Feshbach resonances in the interaction of two heteronuclear group-I atoms. The theory provides a unified and a uniform description of resonances in all partial waves and enables the characterization of a large number of resonances in terms of very few parameters. For the sample system of ${}^6\mathrm{Li} {}^{40}\mathrm{K}$, we present descriptions of all resonances in $aa$, $ab$, and $ba$ channels, in partial waves $s$ ($l=0$) through $h$ ($l=5$), and in a magnetic field of 0–1000 G. All resonances, including those in nonzero partial waves, are fully characterized using the newly developed parametrization of Gao [Phys. Rev. A 84, 022706 (2011)].