The Casimir-Lifshitz interaction between metamaterials is studied using a model that takes into account the structural heterogeneity of the dielectric and magnetic properties of the bodies. A recently developed perturbation theory for the Casimir-Lifshitz interaction between arbitrary material bodies is generalized to include nonuniform magnetic permeability profiles and used to study the interaction between the magneto-dielectric heterostructures within the leading order. The metamaterials are modeled as two-dimensional arrays of domains with varying permittivity and permeability. In the case of two semi-infinite bodies with flat boundaries, the patterned structure of the material properties is found to cause the normal Casimir-Lifshitz force to develop an oscillatory behavior when the distance between the two bodies is comparable to the wavelength of the patterned features in the metamaterials. The nonuniformity also leads to the emergence of lateral Casimir-Lifshitz forces, which tend to strengthen as the gap size becomes smaller. Our results suggest that the recent studies on Casimir-Lifshitz forces between metamaterials, which have been performed with the aim of examining the possibility of observing the repulsive force, should be revisited to include the effect of the patterned structure at the wavelength of several hundred nanometers that coincides with the relevant gap size in the experiments.

We study systems of few two-component fermions interacting via short-range interactions within a harmonic-oscillator trap. The dominant interactions, which are two-body interactions, are organized according to the number of derivatives and defined in a two-body truncated model space made from a bound-state basis. Leading-order (LO) interactions are solved for exactly using the formalism of the no-core shell model, whereas corrections are treated as many-body perturbations. We show explicitly that next-to-LO and next-to-next-to-LO interactions improve convergence as the model space increases. We present results at unitarity for three- and four-fermion systems, which show excellent agreement with the exact solution (for the three-body problem) and results obtained by other methods (in the four-body case). We also present results for finite scattering lengths and nonzero range of the interaction, including (at positive scattering length) observation of a change in the structure of the three-body ground state and extraction of the atom-dimer scattering length.

The quantum walk was originally proposed as a quantum-mechanical analog of the classical random walk, and has since become a powerful tool in quantum information science. In this paper, we show that discrete-time quantum walks provide a versatile platform for studying topological phases, which are currently the subject of intense theoretical and experimental investigations. In particular, we demonstrate that recent experimental realizations of quantum walks with cold atoms, photons, and ions simulate a nontrivial one-dimensional topological phase. With simple modifications, the quantum walk can be engineered to realize all of the topological phases, which have been classified in one and two dimensions. We further discuss the existence of robust edge modes at phase boundaries, which provide experimental signatures for the nontrivial topological character of the system.

We demonstrate a technique based on invariants of motion for a time-dependent Hamiltonian, allowing a fast transition to a final state identical in theory to that obtained through a perfectly adiabatic transformation. This method is experimentally applied to the fast decompression of an ultracold cloud of ${}^{87}\mathrm{Rb}$ atoms held in a harmonic magnetic trap in the presence of gravity. We are able to decompress the trap by a factor of $15$ within $35$ ms with a strong suppression of the sloshing and breathing modes induced by the large vertical displacement and curvature reduction of the trap. When compared to a standard linear decompression, we achieve a gain of a factor of $37$ on the transition time.

We investigate the possibility of a superfluid-ferromagnet-superfluid (SFS) junction in a superfluid Fermi gas. To examine this possibility in a simple manner, we consider an attractive Hubbard model at $T=0$ within the mean-field theory. When a potential barrier is embedded in a superfluid Fermi gas with population imbalance ($N_{\uparrow }>N_{\downarrow }$, where $N_{\sigma }$ is the number of atoms with pseudospin $\sigma =\hspace{0.5em}\uparrow$, $\downarrow$), this barrier is shown to be magnetized in the sense that excess $\uparrow$-spin atoms are localized around it. The resulting superfluid Fermi gas is spatially divided into two by this ferromagnet, so that one obtains a junction similar to the superconductor-ferromagnet-superconductor junction discussed in superconductivity. Indeed, we show that the so-called $\pi$ phase, which is a typical phenomenon in the SFS junction, is realized, where the superfluid order parameter changes its sign across the junction. Our results would be useful for the study of magnetic effects on fermion superfluidity using an ultracold Fermi gas.

We report slowed propagation and storage and retrieval of thermal light in warm rubidium vapor using the effect of electromagnetically induced transparency (EIT). We first demonstrate slowed propagation of the probe thermal light beam through an EIT medium by measuring the second-order correlation function of the light field using the Hanbury-Brown-Twiss interferometer. We also report an experimental study on the effect of the EIT slow-light medium on the temporal coherence of thermal light. Finally, we demonstrate the storage and retrieval of the thermal light beam in the EIT medium. The direct measurement of the photon number statistics of the retrieved light field shows that the photon number statistics are preserved during the storage and retrieval processes.

The Bell and Leggett-Garg tests offer operational ways to demonstrate that nonclassical behavior manifests itself in quantum systems, and experimentalists have implemented these protocols to show that classical worldviews such as local realism and macrorealism are false, respectively. Previous theoretical research has exposed important connections between more general Bell inequalities and polyhedral combinatorics. We show here that general Leggett-Garg inequalities are closely related to the cut polytope of the complete graph, a geometric object well-studied in combinatorics. Building on that connection, we offer a family of Leggett-Garg inequalities that are not trivial combinations of the most basic Leggett-Garg inequalities. We then show that violations of macrorealism can occur in surprising ways, by giving an example of a quantum system that violates the “pentagon” Leggett-Garg inequality but does not violate any of the basic “triangle” Leggett-Garg inequalities.

We present the observation of optomechanical coupling in crystalline whispering-gallery-mode (WGM) resonators. The high purity of the material enables optical quality factors in excess of ${10}^{10}$ and finesse exceeding ${10}^6$, as well as mechanical quality factors greater than ${10}^5$. Ultrasensitive displacement measurements reveal mechanical radial modes at frequencies up to $20$ $\mathrm{MHz}$, corresponding to unprecedentedly high sideband factors ($>$$100$). In combination with the weak intrinsic mechanical damping this renders crystalline WGM microresonators promising for experiments in the classical and quantum regime of optomechanics.

We present several entanglement conditions in order to detect bound entangled states in continuous-variable systems. Specifically, Werner and Wolf [Phys. Rev. Lett. 86, 3658 (2001)] and Horodecki and Lewenstein [Phys. Rev. Lett. 85, 2657 (2000)] have proposed examples of a bound entangled Gaussian state and a bound entangled non-Gaussian state, respectively, of which entanglement can be detected by using our entanglement conditions.

The Born-Oppenheimer potential for the ${}^1{\Sigma }_g^{+}$ state of ${\mathrm{H}}_2$ is obtained in the range $0.1-20$ a.u., using analytic formulas and recursion relations for two-center two-electron integrals with exponential functions. For small distances, the James-Coolidge basis is used, while for large distances, the Heitler-London functions with arbitrary polynomial in electron variables are used. In the whole range of internuclear distance, about ${10}^{-15}$ precision is achieved; as an example, at the equilibrium distance $r=1.4011$ a.u., the Born-Oppenheimer potential amounts to $-1.174\hspace{0.5em}475\hspace{0.5em}931\hspace{0.5em}400\hspace{0.5em}216\hspace{0.5em}7(3)$. Results for the exchange energy verify the formula of Herring and Flicker [Phys. Rev. A 134, 362 (1964)] for the large-internuclear-distance asymptotics. The presented analytic approach to Slater integrals opens a window for high-precision calculations in an arbitrary diatomic molecule.

Long-lived ion-pair states of ${\mathrm{Cl}}_2$ have been observed by delayed pulsed-field ionization in the vicinity of the ${\mathrm{Cl}}^{-}({}^1{\mathrm{S}}_0)+{\mathrm{Cl}}^{+}({}^3{\mathrm{P}}_2)$ dissociation threshold following single-photon excitation from the $X\hspace{0.5em}{}^1{\Sigma }_{\mathrm{g}}^{+}(v=0)$ ground state with a tunable vacuum-ultraviolet laser. The field-ionization spectra reveal a series of resonances corresponding to ion-pair states with effective principal quantum number $n^{*}$ between 1858 and 1876 belonging to a series converging to the ${\mathrm{Cl}}^{-}({}^1{\mathrm{S}}_0)+{\mathrm{Cl}}^{+}({}^3{\mathrm{P}}_0)$ dissociation threshold. These states are observed by forced predissociation into the ${\mathrm{Cl}}^{-}({}^1{\mathrm{S}}_0)+{\mathrm{Cl}}^{+}({}^3{\mathrm{P}}_2)$ ion-pair channel. This process is the ion-pair analog of the process of forced autoionization observed in Rydberg states. The analysis of the spectra and of the field-ionization behavior provides information on the couplings between the relevant ionization and dissociation channels and has enabled the determination of the ion-pair dissociation threshold [$E_{\mathrm{IPD}}({\mathrm{Cl}}^{-}({}^1{\mathrm{S}}_0)+{\mathrm{Cl}}^{+}({}^3{\mathrm{P}}_2))=95\mathrm{\hspace{0.5em}}449.8\pm 1.0\mathrm{\hspace{0.5em}}{\mathrm{cm}}^{-1}$] and of the dissociation energies of ${\mathrm{Cl}}_2\mathrm{\hspace{0.5em}}[{\mathrm{D}}_0(\mathrm{X}\mathrm{\hspace{0.5em}}\mathrm{\hspace{0.5em}}{}^1{\mathrm{\Sigma }}_{\mathrm{g}}^{+})=19\mathrm{\hspace{0.5em}}998.4\pm 1.1\mathrm{\hspace{0.5em}}{\mathrm{cm}}^{-1}]$ and ${\mathrm{Cl}}_2^{+}\mathrm{\hspace{0.5em}}[{\mathrm{D}}_0({\mathrm{X}}^{+}{\mathrm{\hspace{0.5em}}}^2{\mathrm{\Pi }}_{\mathrm{u}})=31\mathrm{\hspace{0.5em}}942.1\pm 1.5\mathrm{\hspace{0.5em}}{\mathrm{cm}}^{-1}]$.

The fluctuating part of the total photoionization cross sections up to the 20th single ionization threshold from the ground state of helium are investigated within a planar model of the atom. The calculated fluctuations reproduce existing experimental observations rather well. The fluctuations are mainly due to a dominant series of resonances which can be associated with an approximate quantum number $F=N-K$. As the energy approaches the double ionization threshold, the dominant role of a single series as sole contributor is apparently lost as new series start to contribute significantly to the cross sections.

An excitation scheme is proposed for transferring population between ground-vibrational levels of a molecule. The transfer is accomplished by pumping and dumping population with a pair of coherent ultrashort-pulse trains via a stationary state. By mismatching the teeth of the frequency combs associated with the pulse trains to the vibrational levels, high selectivity in the excitation, along with high transfer efficiency, is predicted. The pump-dump scheme does not suffer from spontaneous emission losses, it is insensitive to the pump-dump-train delay, and it requires only basic pulse shaping.

The ionization and fragmentation of molecular silane is examined here with laser intensities ranging between $7\times {10}^{12}$ and $1\times {10}^{15}$ W/cm${}^2$ at $624$ nm. The ionization potential of silane determined using both multiphoton ionization (MPI) and tunneling ionization (TI) models agrees with the vertical ionization potential of the molecule. In addition, the application of the tunneling ionization model is extended here to the fragments of silane to determine their appearance potentials. MPI values for SiH${}_3{}^{+}$, SiH${}_2{}^{+}$, SiH${}^{+}$, Si${}^{+}$, as well as ${\mathrm{H}}_2{}^{+}$ and ${\mathrm{H}}^{+}$ are consistent with vertical potentials, whereas the TI measurements are found to be in accord with adiabatic potentials. The tunneling appearance potentials observed for the fragments ${\mathrm{H}}_2{}^{+}$ and ${\mathrm{H}}^{+}$ are lower than reported for other techniques. In fact, the appearance potential measurements for these species resulting from silane are lower than their ionization potentials. The fragmentation rate of silane is determined to be nearly $20$ times larger than the ionization rate. The main precursor for producing amorphous silicon ($a$-Si:H) thin films, SiH${}_3{}^{+}$ is the dominant fragmentation product making up roughly a third of the total ion yield, a substantial increase from other techniques.

We study positron-impact ionization of atomic hydrogen in the presence of a linearly polarized laser field in the second Born approximation. The state of the fast incident positron is described by the Volkov wave function and the dressed state of the ejected electron and ground-state hydrogen are treated as a first-order time-dependent perturbative wave function. We calculate the triple differential cross section in the Ehrhardt asymmetric geometry, and numerical results indicate that the second-order effects are significant. Compared with the ionization process by electrons, the influence of the projectile charge sign appears: the binary peaks are greatly enhanced for positrons in the second Born approximation.

We investigate the dynamics of double ionization of He atom by an intense near-infrared and an attosecond vacuum ultraviolet (VUV) laser pulse, which are either applied in sequence or at the same time. To this end we solve the time-dependent Schrödinger equation for a two-electron model atom interacting with the two fields. We compare the double-ionization yields and probability density distributions, with and without the application of the attosecond pulse, for the different scenarios. The results of our numerical simulations show how ionization or excitation of the neutral atom by a preceding or simultaneously applied VUV pulse affects the double-ionization dynamics driven by the near-infrared laser pulse. The findings provide insights regarding the question if attosecond technology can be used to temporally resolve mechanisms of correlated emission of electrons in a strong laser field.

Using the finite-element discrete variable representation of the nonequilibrium Green’s function (NEGF) we extend previous work [K. Balzer et al., Phys. Rev. A 81, 022510 (2010)] to nonequilibrium situations and compute—from the two-time Schwinger-Keldysh-Kadanoff-Baym equations—the response of the helium atom and the heteronuclear molecule lithium hydride to laser fields in the uv and xuv regimes. In particular, by comparing the one-electron density and the dipole moment to time-dependent Hartree-Fock results on one hand and the full solution of the time-dependent Schrödinger equation on the other hand, we demonstrate that the time-dependent second Born approximation carries valuable information about electron-electron correlation effects. Also, we outline an efficient distributed memory concept which enables a parallel and well-scalable algorithm for computing the NEGF in the two-time domain.

We show that a two-species mixture of polar molecules trapped on an optical lattice gives rise to a system of rotational excitons in the presence of tunable impurities. The exciton-impurity interactions can be controlled by an external electric field, which can be exploited for quantum simulation of localization phenomena in disordered media. We demonstrate that an external electric field can be used to induce resonant enhancement of the exciton-impurity scattering cross sections and delocalization of excitonic states in a correlated one-dimensional disorder potential.

We derive upper bounds on the statistics of phase and phase difference that are satisfied by all classical states. They are obtained by finding the maximum projection of classical states on phase states. For a single-mode phase, meaningful bounds are obtained conditioned to a fixed mean number of photons. We also derive classical bounds for the projection on phase-coherent states, discussing their relation with phase-state bounds within the context of analytic representations. We find states with nonclassical phase properties disclosed by the violation of these classical bounds. These are quadrature and SU($2$) squeezed states and phase-coherent states.

We show that the frequently encountered physical model of a monochromatically driven two-level system is exactly solvable. We present an analytical exact solution to this driven system in terms of two known special functions. Our analytical solution is valid for all parameter regimes and may find applications in current solid-state experiments.