Optical Fano resonances are an increasingly important line-shape engineering tool with applications ranging from high-sensitivity sensing and ultrasmall lasers to low-power optical switching or modulating. Here we demonstrate a fully on-chip resonant nanostructure on a photonic crystal molecule platform exhibiting typical double- and Ramsey-Fano resonances, which can be actively controlled by the modification of the blockade transmittance in the waveguide. First, we investigate the transmission spectrum of a coupled double-cavity setting, showing a kind of double-Fano resonance line shape which consists of an asymmetric low-frequency Fano (LF) resonance and a high-frequency Fano (HF) resonance. At the same time, we elucidate the influences of various physical quantities on the generated LF and HF resonances. Second, and more interestingly, we reveal the occurrence of the Ramsey-Fano resonance profile by extending a double-cavity arrangement to a coupled-cavity-array arrangement. This Ramsey-Fano resonance can be attributed to the multiple quantum interference among a variety of light pathways. Finally, as an application, we discuss how to use an asymmetric double-Fano resonance line shape, which features the steep spectral slope, to improve the sensing performance. Our obtained results may stimulate future experimental efforts in controlling the double- and Ramsey-Fano resonance line shapes of this system more accurately.

We computationally study the resolution limits for three-dimensional coherent x-ray diffractive imaging of heavy, nonbiological systems using Ar clusters as a prototype. We treat electronic and nuclear dynamics on an equal footing and remove the frozen-lattice approximation often used in electronic damage studies. We explore the achievable resolution as a function of pulse parameters (fluence level, pulse duration, and photon energy) and particle size. The contribution of combined lattice and electron dynamics is not negligible even for 2 fs pulses, and the Compton scattering is less deleterious than in biological systems for atomic-scale imaging. Although free-electron scattering represents a significant background, we find that recovery of the original structure is in principle possible with 3 Å resolution for particles of 11 nm diameter.

Generalized squeezing rotating-wave approximation (GSRWA) is proposed by employing both the displacement and the squeezing transformations. A solvable Hamiltonian is reformulated in the same form as the ordinary RWA ones. For a qubit coupled to oscillators experiment, a well-defined Schrödinger-cat-like entangled state is given by the displaced-squeezed oscillator state instead of the original displaced state. For the isotropic Rabi case, the mean photon number and the ground-state energy are expressed analytically with additional squeezing terms, exhibiting a substantial improvement of the GSRWA. And the ground-state energy in the anisotropic Rabi model confirms the effectiveness of the GSRWA. Due to the squeezing effect, the GSRWA improves the previous methods only with the displacement transformation in a wide range of coupling strengths even for large atom frequency.

We derive a microscopic model for dissipative dynamics in a system of mutually interacting qubits coupled to a thermal bath that generalizes the dissipative model of Landau-Lifshitz-Gilbert to the case of anisotropic bath couplings. We show that the dissipation acts to bias the quantum trajectories towards a reduced phase space. This model applies to a system of superconducting flux qubits whose coupling to the environment is necessarily anisotropic. We study the model in the context of the D-Wave computing device and show that the form of environmental coupling in this case produces dynamics that are closely related to several models proposed on phenomenological grounds.

We investigate both theoretically and experimentally the dynamics of entanglement and nonlocality for two qubits immersed in a global pure dephasing environment. We demonstrate the existence of a class of states for which entanglement is forever frozen during the dynamics, even if the state of the system does evolve. At the same time nonlocal correlations, quantified by the violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality, either undergo sudden death or are trapped during the dynamics.

We consider the problem of estimating multiple phases using a multimode interferometer. In this setting we show that while global strategies that estimate all the phases simultaneously can lead to high precision gains, the same enhancements can be obtained with local strategies in which each phase is estimated individually. A key resource for the enhancement is shown to be a large particle-number variance in the probe state, and for states where the total particle number is not fixed, this can be obtained for mode-separable states, and the phases can be read out with local measurements. This has important practical implications because local strategies are generally preferred to global ones for their robustness to local estimation failure, flexibility in the distribution of resources, and comparatively easier state preparation. We obtain our results by analyzing two different schemes: the first uses a set of interferometers, which can be used as a model for a network of quantum sensors, and the second looks at measuring a number of phases relative to a reference, which is concerned primarily with quantum imaging.

We have observed short-range photoassociation of ${}^7\mathrm{Li}{}^{85}\mathrm{Rb}$ to the two lowest vibrational states of the $d{}^3\mathrm{\Pi }$ potential. We have also observed several $a^3{\mathrm{\Sigma }}^{+}$ vibrational levels with generation rates between $\sim {10}^2$ and $\sim {10}^3$ molecules per second, resulting from the spontaneous decay of these $d{}^3\mathrm{\Pi }$ molecules. We observe an alternation of the peak heights in the rotational photoassociation spectrum that depends on the parity of the excited molecular state. Franck-Condon overlap calculations predict that photoassociation to higher vibrational levels of the $d{}^3\mathrm{\Pi }$ potential, in particular, the sixth vibrational level, should populate the lowest vibrational level of the $a{}^3{\mathrm{\Sigma }}^{+}$ state at a rate as high as ${10}^4$ molecules per second. This work also motivates an experimental search for short-range photoassociation to other bound molecular states, such as $c{}^3{\mathrm{\Sigma }}^{+}$ or $b{}^3\mathrm{\Pi }$, as prospects for preparing ground-state molecules.

We present a theoretical study of the mixed-field-orientation of asymmetric-top molecules in tilted static electric field and nonresonant linearly polarized laser pulse by solving the time-dependent Schrödinger equation. Within this framework, we compute the mixed-field orientation of a state-selected molecular beam of benzonitrile $\left({\mathrm{C}}_7{\mathrm{H}}_5\mathrm{N}\right)$ and compare with the experimental observations [J. L. Hansen et al., Phys. Rev. A 83, 023406 (2011)] and with our previous time-independent descriptions [J. J. Omiste et al., Phys. Chem. Chem. Phys. 13, 18815 (2011)]. For an excited rotational state, we investigate the field-dressed dynamics for several field configurations as those used in the mixed-field experiments. The nonadiabatic phenomena and their consequences on the rotational dynamics are analyzed in detail.

Time delays of electrons emitted from an isotropic initial state with the absorption of a single photon and leaving behind an isotropic ion are angle independent. Using an interferometric method involving XUV attosecond pulse trains and an IR-probe field in combination with a detection scheme, which allows for full three-dimensional momentum resolution, we show that measured time delays between electrons liberated from the $1s^2$ spherically symmetric ground state of helium depend on the emission direction of the electrons relative to the common linear polarization axis of the ionizing XUV light and the IR-probing field. Such time delay anisotropy, for which we measure values as large as 60 as, is caused by the interplay between final quantum states with different symmetry and arises naturally whenever the photoionization process involves the exchange of more than one photon. With the support of accurate theoretical models, the angular dependence of the time delay is attributed to small phase differences that are induced in the laser-driven continuum transitions to the final states. Since most measurement techniques tracing attosecond electron dynamics involve the exchange of at least two photons, this is a general and significant effect that must be taken into account in all measurements of time delays involving photoionization processes.

As light propagates through a medium, absorption caused by electronic or rovibrational transitions is evident in the transmitted spectrum. The incident electromagnetic field polarizes the medium and the absorption is due to the imaginary part of the linear susceptibility. In the time domain, the field establishes a coherence in the medium that radiates out of phase with the initial field. This coherence can persist for tens of picoseconds in atmospheric molecules such as ${\mathrm{H}}_2\mathrm{O}$. We propagate a few-cycle laser pulse centered at $1.8\mu \mathrm{m}$ through the atmosphere and measure the long-lasting molecular coherence in the time domain by high-order harmonic cross correlation. The measured optical free-induction decay of the pulse is compared with a calculation based on the calculated rovibrational spectrum of ${\mathrm{H}}_2\mathrm{O}$ absorption.

Shortcuts to adiabaticity in various quantum systems have attracted much attention with their wide applications in quantum information processing and quantum control. In this paper, we concentrate on a stimulated Raman shortcut-to-adiabatic passage in quantum three-level systems. To implement counterdiabatic driving but without additional coupling, we first reduce the quantum three-level systems to effective two-level problems at large intermediate-level detuning, or on resonance, apply counterdiabatic driving along with the unitary transformation and eventually modify the pump and Stokes pulses for achieving fast and high-fidelity population transfer. The required laser intensity and stability against parameter variation are further discussed, to demonstrate the advantage of shortcuts to adiabaticity.

We present a full theoretical analysis of quasi-phase-matching (QPM) in three-dimensional (3D) periodic structures and point up optimum nonlinear structures, which promote the best nonlinear conversion efficiencies and are close to real structures. The QPM properties of 14 Bravais lattices are investigated as a function of motifs (orthorhombic and spherical) and of modulation types (“+/–” and “+/0”). This full 3D QPM theory allows us to produce all results of one- and two-dimensional QPM structures by choosing appropriate lattice periodicity and motif. The optimization of nonlinear conversion efficiencies in 3D QPM is obtained by analyzing four particular structures (simple cubic, body-centered cubic, face-centered cubic, and diamond cubic lattices) with different filling factors and motifs. In particular, 3D structures, which are very close to those realized in practice, are proposed and simulated, creating a guide for fabrication of real optimum QPM structures.

Solitons play a fundamental role in the dynamics of nonlinear excitations. Here we explore the motion of solitons in one-dimensional Bose-Einstein condensates subjected to a spin-orbit coupling (SOC). We demonstrate that the spin dynamics of solitons is governed by a nonlinear Bloch equation. The spin dynamics affects the orbital motion of solitons leading to spin-orbit effects in the dynamics of macroscopic quantum objects (mean-field solitons). The latter perform oscillations with a frequency determined by the SOC, Raman coupling, and intrinsic nonlinearity. These findings reveal unique features of solitons affected by the SOC, which are confirmed by analytical considerations and numerical simulations of the underlying Gross-Pitaevskii equations.

We present an efficient proposal for error-rejecting quantum computing with quantum dots (QDs) embedded in single-sided optical microcavities based on the interface between the circularly polarized photon and QDs. An almost unity fidelity of the quantum entangling gate (EG) can be implemented with a detectable error that leads to a recycling EG procedure, which improves further the efficiency of our proposal along with the robustness to the errors involved in imperfect input-output processes. Meanwhile, we discuss the performance of our proposal for the EG on two solid-state spins with currently achieved experiment parameters, showing that it is feasible with current experimental technology. It provides a promising building block for solid-state quantum computing and quantum networks.

We present a simplified model for dynamical diffraction of particles through a periodic thick perfect crystal based on repeated application of a coherent beam-splitting unitary at coarse-grained lattice sites. By demanding translational invariance and a computationally tractable number of sites in the coarse graining, we show how this approach reproduces many results typical of dynamical diffraction theory and experiments. This approach has the benefit of being applicable in the thick, thin, and intermediate crystal regimes. The method is applied to a three-blade neutron interferometer to predict the output beam profiles, interference patterns, and contrast variation.

Two recent experimental papers reported the first measurements of absolute two-photon-ionization cross sections $\sigma \left(2\right)$ of helium, for EUV wavelengths, using free-electron laser (FEL) pulses [Sato et al., J. Phys. B 44, 161001 (2011); Fushitani et al., Phys. Rev. A 88, 063422 (2013)]. The wavelengths correspond to transitions that are off resonance as well as on resonance with the $1s2p$ and $1s3p{}^1{P}^o$ Rydberg states. Inspection of their results reveals considerable discrepancies, while their comparison with theoretical results obtained earlier from time-independent calculations, one perturbative and two nonperturbative ones, cannot lead to secure conclusions as to the true values of $\sigma \left(2\right)$. We examined this prototypical problem by implementing a time-dependent approach, which utilizes the nonperturbative solution of the time-dependent Schrödinger equation. This solution was obtained in terms of the state-specific expansion approach, in an upgraded version where the coupling matrix elements are computed using the full electric operator of the multipolar Hamiltonian. The $\sigma \left(2\right)$ were obtained for pulses of 300 fs, as in the 2011 FEL experiment. Their computation was achieved by fitting the time-dependent ionization survival probability to $e^{-\mathrm{\Gamma }t}$, where $\mathrm{\Gamma }$ is the rate of ionization. The wavelengths and intensities are those of the FEL experiments, as well as others, such as the wavelengths 52.22 and 51.56 nm, for which the $1s4p{}^1{P}^o$ and $1s5p{}^1{P}^o$ levels are on resonance with the initial ${}^{1}S$ state. Apart from the predictions for these wavelengths, the paper contains characteristic comparisons among all the results on these EUV $\sigma \left(2\right)$, experimental and theoretical. In general, the trends predicted by nonperturbative methods are confirmed by the FEL measurements. However, discrepancies exist among the absolute numbers. Furthermore, comparison among the results of the three nonperturbative approaches (present time-dependent and two earlier time-independent ones published in 1999 and 2005) indicates an overall consistency, although quantitative differences for individual cases are apparent.

Nonlocal potential models have been used in place of the Coulomb potential in the Schrödinger equation as an efficient means of exploring high-field laser-atom interaction in previous works. Although these models have found use in modeling phenomena including photoionization and ejected electron momentum spectra, they are known to break electromagnetic gauge invariance. This paper examines if there is a preferred gauge for the linear field response and photoionization characteristics of nonlocal atomic binding potentials in the length and velocity gauges. It is found that the length gauge is preferable for a wide range of parameters.

The dynamic localization of a two-level atom in a periodic potential under the action of spin-orbit coupling and a weak harmonically varying linear force is studied. We consider optical and Zeeman potentials that are either in phase or out of phase in two spinor components, respectively. The expectation value for the position of the atom after one oscillation period of the linear force is recovered in authentic resonances or in pseudoresonances. The frequencies of the linear force corresponding to authentic resonances are determined by the band structure of the periodic potential and are affected by the spin-orbit coupling. The width or dispersion of the wave packet in authentic resonances is usually minimal. The frequencies corresponding to pseudoresonances do not depend on the type of potential and on the strength of the spin-orbit coupling, while the evolution of excitations at the corresponding frequencies is usually accompanied by significant dispersion. Pseudoresonances are determined by the initial phase of the linear force and by the quasimomentum of the wave packet. Due to the spinor nature of the system, the motion of the atom is accompanied by periodic, but not harmonic, spin oscillations. Under the action of spin-orbit coupling the oscillations of the wave packet can be nearly completely suppressed in optical lattices. Dynamic localization in Zeeman lattices is characterized by doubling of the resonant oscillation periods due to band crossing at the boundary of the Brillouin zone. We also show that higher harmonics in the Fourier expansion of the energy band lead to effective dispersion, which can be strong enough to prevent dynamic localization of the Bloch wave packet.

We study three-dimensional Bose and Fermi gases in the upper branch, a phase defined by the absence of bound states in the repulsive interaction regime, within an approximation that considers only two-body interactions. Employing a formalism based on the $S$ matrix, we derive useful analytic expressions that hold on the upper branch in the weak coupling limit. We determine upper branch phase diagrams for both bosons and fermions with techniques valid for arbitrary positive scattering length.

We investigate the phenomenon of optical bistability in a driven ensemble of Rydberg atoms. By performing two experiments with thermal vapors of rubidium and cesium, we are able to shed light on the underlying interaction mechanisms causing such a nonlinear behavior. Due to the different properties of these two atomic species, we conclude that the large polarizability of Rydberg states in combination with electric fields of spontaneously ionized Rydberg atoms is the relevant interaction mechanism. In the case of rubidium, we directly measure the electric field in a bistable situation via two-species spectroscopy. In cesium, we make use of the different sign of the polarizability for different $l$ states and the possibility of applying electric fields. Both these experiments allow us to rule out dipole-dipole interactions and support our hypothesis of a charge-induced bistability.