We explore the time evolution of correlations in a homogeneous gas of lattice bosons with filling factor $n_0$, following a sudden reduction in the lattice depth to a regime where the interactions are weak. In the limit of vanishing interactions, we find a simple closed-form expression for the static structure factor. The corresponding real-space density-density correlation function shows multiple spatial oscillations which disperse linearly in time. By perturbatively including the effect of interactions, we study the evolution of boson quasimomentum distribution following the quench. In one dimension, the quasimomentum distribution develops peaks at finite momentum which disperse towards $q=\pm \pi /2$. In two dimensions, the momentum occupation rapidly approaches a steady-state distribution characterized by a broad peak at $q=0$. Quasi-long-range order is never found at finite time. Our studies provide insight into the dynamics of isolated quantum systems.

The repulsive and restoring Casimir force between anisotropic single-negative metamaterial slabs is investigated. Both theoretical and numerical calculations demonstrate the influence of the direction-dependent electromagnetic properties of the metamaterial on the Casimir effect. The electromagnetic responses of the metamaterial parallel and perpendicular to the optical axis affect the Casimir force differently. The polarity of the force as well as its relation to the slab separation are discussed. In the particular case of the restoring Casimir force, we show that multiple equilibria of the force can be formed based on the anisotropy of the single-negative metamaterial.

We report on a narrow linewidth laser diode system that is stabilized using both optical and electronic feedback to a spectral hole in cryogenic Tm:YAG. The large group delay of the spectral hole leads to a laser with very low phase noise. The laser has proved useful for quantum optics and sensing applications involving cryogenic rare-earth-ion dopants.

Noncollinear six-wave mixing of femtosecond light pulses in air by two crossed laser beams has been demonstrated. It was shown that within a wide range of laser intensities this process leads to efficient third-order-harmonic generation, which indicates the importance of higher-order optical nonlinearities in intense light-matter interactions. A direct comparison of the experiment and theory allowed us to estimate unambiguously the magnitude of the quintic optical nonlinearity ${\chi }_{xyyyyx}^{\left(5\right)}(-3\omega ;\omega ,\omega ,\omega ,\omega ,-\omega )$ of air as $2\times {10}^{-49}$ (m/V)${}^4$. We expect that this technique could be useful for multiphoton spectroscopy and laser frequency conversion, as well as for ultrashort light-pulse characterization and verification of theoretical models describing propagation of powerful laser pulses in gaseous media.

Mie scattering theory is used to calculate radiation forces on a dielectric microsphere illuminated by evanescent waves, produced by laser light transmitted obliquely through a flat horizontal dielectric surface. The incident field is identified with the evanescent field, and both $p$ and $s$ polarizations are considered. Our investigation consists of three parts. First, after highlighting the basic formalism, we report results for the radiation force published in an earlier paper [J. Opt. Soc. Am. B 12, 2429 (1995)], correcting a few trivial calculational errors. Second—the main objective of our paper—is to show how the vertical (lifting) force on microspheres, typically via a proper adjustment of the laser frequency, can be used to separate spheres differing by a slight amount in their refractive index. This is caused by an oscillatory behavior in the force with respect to the nondimensional wave number $\alpha$ in the surrounding medium. Fine tuning the wave number $\alpha$, relative to the given refractive indices in the system, may lead to particle expulsion. The sorting mechanism turns out to be feasible when $\alpha$ is about 18–20 or larger, which actually is in the region of practical interest. Finally, we investigate how variations in the angle of incidence ${\theta }_1$ for the laser beam influences the resulting radiation force.

We analyze an electron-hole asymmetry model for simultaneous two-state operation in semiconductor quantum dot lasers. From the linearized equations, we determine simple analytical expressions for the relaxation oscillation (RO) frequencies. Of particular interest is the fact that different expressions for the RO frequencies are obtained depending on the relative values of the photon lifetime and the basic time scale of the nonlinear intradot interaction. If comparable, we find only one frequency that depends on a combination of the two-state intensities.

We compare results of the recent experiment by Herath et al. [T. Herath, L. Yan, S. K. Lee, and W. Li, Phys. Rev. Lett. 109, 043004 (2012)] on strong-field nonadiabatic tunneling in circularly polarized laser fields with the original predictions of our theory [I. Barth and O. Smirnova, Phys. Rev. A 84, 063415 (2011)] that stimulated these experiments. We show that the theory and experiment are in very good agreement. We also explain why the initial comparison performed by Herath et al. [T. Herath, L. Yan, S. K. Lee, and W. Li, Phys. Rev. Lett. 109, 043004 (2012)] has suggested quantitative discrepancies with our theory. We confirm that these seeming discrepancies are removed with an accurate application of our theoretical model. We suggest an experiment for unique determination of the ionization preference of valence orbitals $p_{+}$ or $p_{-}$.

We illustrate an alternate mechanism which causes probe transparency in a Doppler-broadened V-type system. Our numerical results obtained for very low control field amplitudes clearly indicate the feasibility of attaining nearly perfect probe transparency that originates from an additional one-photon coherence induced by the control field in a Doppler-broadened V-type system. In this regime of control field amplitudes, the criterion for electromagnetically induced transparency (EIT) is not fulfilled and hence the contribution of the usual EIT term is found to be negligible.

Spectra and measured wavelengths of intrashell $n=3$ transitions in highly charged tungsten ions with partially filled $3p$ and $3d$ valence shells, Al-like W${}^{61+}$ through Fe-like W${}^{48+}$, are presented. The ions were created and excited at the electron-beam ion-trap facility at the Lawrence Livermore National Laboratory and measured with a high-resolution grazing-incidence spectrometer. The spectral lines were studied in the 27–41 Å range and were analyzed by a comparison with synthetic spectra based on a collisional-radiative model. We determined that the emission includes not only electric-dipole-allowed transitions, but also several electric-quadrupole and magnetic-dipole transitions. Line-position uncertainties as low as 25 ppm were achieved. Thus, our measurements provide much-needed benchmarks for calculations of the atomic structure of highly charged ions with a partially filled subshell, since these ions are difficult to calculate due to electron-correlation effects.

Blue-detuned dipole traps and their ability to preserve atomic coherences are interesting for precision measurement applications. In this paper, we present experimental studies on the differential ac Stark shift of the ground-state hyperfine splitting in ${}^{87}$Rb atoms confined in a dynamic blue-detuned dipole trap. We systematically study the power and detuning effects on the Rabi resonance frequency (differential ac Stark shift) and its linewidth (coherence) and find that their performance is compatible with future parity violation experiments in Fr.

We derive a governing equation for a Kelvin wave supported on a vortex line in a Bose-Einstein condensate, in a rotating cylindrically symmetric parabolic trap, where it is assumed that the shape of the vortex line is dominated by the properties of the condensate at the center of the trap. From this solution the Kelvin wave dispersion relation is determined. In the limit of an oblate trap and in the absence of longitudinal trapping our results are consistent with previous work. We show that the derived Kelvin wave dispersion in the general case is in quantitative agreement with numerical calculations of the Bogoliubov spectrum.

We present a theoretical analysis of the spectral features of coherent light pulses traveling in a one-dimensional waveguide with an embedded two-level quantum system. In particular, we clarify and explain the relevant physical mechanisms that lead to a rich variety of distinct features in the spectrum of the scattered light. This includes the phenomenon of discrete steps in the transmitted intensity as a function of the excitation amplitude, frequency mixing as a consequence of cascaded nonlinear processes, and the role of atom-photon bound states.

Based on our experimental observations of the resonant stimulated Raman gain and loss spectra in Rb atomic vapor, we propose an alternative interpretation of electromagnetically induced transparency (EIT). We find that, in the presence of a coupling field, a probe beam can exhibit both gain and loss depending on the frequencies of the incident beams. The gain and loss can coexist in a Doppler-broadened system, leading to polarization interference between atoms of different velocities, with a sharp transition from gain to loss as the probe-field frequency is scanned. We use the concept of Raman gain, instead of the commonly accepted quantum Fano interference, to explain the phenomenon of EIT and its transparency window as being due to the suppression of linear absorption by the Raman gain. Using this concept, the phenomena of EIT and Autler-Townes splitting may be explained within the same framework.

We develop a general theory to study the electromagnetically induced transparency (EIT) in ultracold quantum gases, applicable for both Bose and Fermi gases with an arbitrary interparticle interaction strength. We show that, in the weak probe field limit, the EIT spectrum is solely determined by the single-particle Green's function of the ground-state atoms, and reflects interesting quantum many-body effects when atoms are virtually coupled to the low-lying Rydberg states. As an example, we apply our theory to a one-dimensional Luttinger liquid, a Bose-Mott insulator state, and the superfluid state of two-component Fermi gases, and show how the many-body features can be observed nondestructively in the unconventional EIT spectrum.

Production of electron-positron pairs from vacuum in the combined electromagnetic fields of a high-intensity laser pulse and an atomic nucleus is studied within the framework of laser-dressed quantum electrodynamics. The focus lies on the influence exerted by a finite laser pulse length on the energy spectra of created electrons and positrons, which is examined in a broad range of field frequencies and intensities. The results for an isolated short laser pulse are also compared with corresponding calculations for an infinite train of laser pulses. It is shown that the laser pulse length and its carrier-envelope phase have a substantial effect on the pair creation process, leading to both quantitative and qualitative differences in the particle spectra.

We investigate the two-photon transport through a waveguide side coupling to a whispering-gallery-atom system. Using the Lehmann-Symanzik-Zimmermann reduction approach, we present the general formula for the two-photon processes including the two-photon scattering matrices, the wave functions, and the second order correlation functions of the outgoing photons. Based on the exact results of the second order correlation functions, we analyze the quantum statistics behaviors of the outgoing photons for two different cases: (a) the ideal case without the intermodal coupling in the whispering-gallery resonator; and (b) the case in the presence of the intermodal coupling which leads to more complex nonlinear behavior. In the ideal case, we show that the system consists of two independent scattering pathways, a free pathway by a cavity mode without atomic excitation, and a “Jaynes-Cummings” pathway described by the Jaynes-Cummings Hamiltonian of a single-mode cavity coupling to an atom. The presence of the free pathway leads to two-photon correlation properties that are distinctively different from the standard Jaynes-Cummings model, in both the strong and weak-coupling regime. In the presence of intermodal mixing, the system no longer exhibits a free resonant pathway. Instead, both the single-photon and the two-photon transport properties depend on the position of the atom. Thus, in the presence of intermodal mixing, one can in fact tune the photon correlation properties by changing the position of the atom. Our formalism can be used to treat resonator and cavity dissipation as well.

We study two-photon scattering of a tightly focused weak light beam from a small atomic ensemble of two-level atoms (2LAs). This is similar to the scattering of photons from an atomic ensemble in a one-dimensional waveguide. The scaling of two-photon nonlinearity at single-photon resonance shows a nonmonotonic behavior with an increasing number of few identical 2LAs. The two-photon nonlinearity decays monotonically with an increasing number of atoms for incident photons detuned from single-photon resonance. Single-photon transport in two 2LAs is similar to that in a single $V$-type three-level atom (3LA). However, two-photon transport in these two systems shows very different line shapes. When single-photon transmission is zero in these systems, two transmitted photons are bunched together in a $V$-type 3LA, while their correlation is zero in two 2LAs. The difference in the two-photon line shape persists for few 2LAs and 3LAs. Therefore, the two-photon scattering of a tightly focused weak light beam can be used as a probe to detect atomic level structures of different atoms with similar transition energies.

We explore protocols for three-state adiabatic passage where the tunnel matrix elements are varied digitally, rather than smoothly as is the case with conventional adiabatic passage. In particular, we focus on stimulated Raman adiabatic passage and related three-state schemes where the control is applied stepwise, with either equal spaced levels for the tunnel matrix elements or uniform pulse lengths. Our results show that the evolution typically shows the hallmarks of conventional adiabatic passage, although with additional resonances exhibiting no state transfer.

We show that quantum designs characterize the general structure of the optimal approximation of the transpose map on quantum states. Based on this characterization, we propose an implementation of the approximate transpose map by a measurement-and-preparation scheme. The results show that state manipulation in quantum two-designs suffices for transpose-based quantum-information applications. In particular, we present how these results can be applied to the framework of detecting multipartite entangled states, for instance, when local measurements or interferometry-based experimental approaches are applied.