State-selective and total single-electron-capture cross sections in collisions of H${}^{+}$ with the excited Li${}^{*}$(2p) atom have been investigated by using the full quantum-mechanical molecular orbital close-coupling (QMOCC) method in the energy range 0.001–3 keV/u and by the two-center atomic orbital close-coupling (TC-AOCC) method in the energy range 0.1–100 keV/u. The present results are also compared with data from other sources when available. It is found that the total and partial electron-capture cross sections are sensitive to the initial p-state charge cloud alignment, particularly in the low-energy region.

We report a mechanism and a realizable approach for the coherent control of the generation of an isolated and ultrashort attosecond (as) laser pulse from atoms by optimizing the two-color laser fields with a proper time delay. Optimizing the laser pulse shape allows the control of the electron quantum paths and enables high-harmonic generation from the long- and short-trajectory electrons to be enhanced and split near the cutoff region. In addition, it delays the long-trajectory electron emission time and allows the production of extremely short attosecond pulses in a relatively narrow time duration. As a case study, we show that an isolated 30 as pulse with a bandwidth of 127 eV can be generated directly from the contribution of long-trajectory electrons alone.

We show that dipolar interactions between ultracold polar alkali-metal dimers in optical lattices can be used to realize a highly tunable generalization of the $t$-$J$ model, which we refer to as the $t$-$J$-$V$-$W$ model. The model features long-range spin-spin interactions $J_z$ and $J_{\perp }$ of $XXZ$ type, long-range density-density interaction $V$, and long-range density-spin interaction $W$, all of which can be controlled in both magnitude and sign independently of each other and of the tunneling $t$. The “spin” is encoded in the rotational degree of freedom of the molecules, while the interactions are controlled by applied static electric and continuous-wave microwave fields. Furthermore, we show that nuclear spins of the molecules can be used to implement an additional (orbital) degree of freedom that is coupled to the original rotational degree of freedom in a tunable way. The presented system is expected to exhibit exotic physics and to provide insights into strongly correlated phenomena in condensed-matter systems. Realistic experimental imperfections are discussed.

We study the real-time dynamics of the Bose-Hubbard model in the presence of time-dependent hopping, allowing for a finite-temperature initial state. We use the Schwinger-Keldysh technique to find the real-time strong coupling action for the problem at both zero and finite temperature. This action allows for the description of both the superfluid and Mott-insulating phases. We use this action to obtain dynamical equations for the superfluid order parameter as hopping is tuned in real time so that the system crosses the superfluid phase boundary. We find that under a quench in the hopping, the system generically enters a metastable state in which the superfluid order parameter has an oscillatory time dependence with a finite magnitude, but disappears when averaged over a period. We relate our results to recent cold-atom experiments.

We systematically studied the lasing characteristics in photonic polycrystalline and amorphous structures. 2D arrays of air holes were fabricated in a GaAs membrane. InAs quantum dots embedded in the membrane provide gain for lasing under optical pumping. The lasing modes are spatially localized, and blue shift as the structural order becomes short ranged. Our three-dimensional numerical simulations reveal that the out-of-plane leakage of the lasing mode dominates over the in-plane leakage. The lasing modes in a photonic polycrystalline move away from the center frequency of the photonic band gap to reduce the out-of-plane leakage. In a photonic amorphous structure, the short-range order improves optical confinement and enhances the quality factor of resonances. Understanding the behavior of photonic polycrystalline laser and amorphous laser opens the possibility of controlling lasing characteristic by varying the degree of structural order.

The polarization dependence of double-resonance optical pumping (DROP) in the ladder-type electromagnetically induced transparency (EIT) of the $5S_{1/2}-5P_{3/2}-5D_{5/2}$ transition of ${}^{87}$Rb atoms is studied. The transmittance spectra in the $5S_{1/2}(F=2)-5P_{3/2}(F^{\prime }=3)-5D_{5/2}(F^{\prime \prime }=2,3,4)$ transition were observed as caused by EIT, DROP, and saturation effects in the various polarization combinations between the probe and coupling lasers. The features of the double-structure transmittance spectra in the $5S_{1/2}(F=2)-5P_{3/2}(F^{\prime }=3)-5D_{5/2}(F^{\prime \prime }=4)$ cycling transition were attributed to the difference in saturation effect according to the transition routes between the Zeeman sublevels and the EIT according to the two-photon transition probability.

Recently [Sivan and Pendry, Phys. Rev. Lett. 106, 193902 (2011)], we have shown that the wave front of short pulses can be accurately and efficiently reversed by use of simple one-dimensional zero-gap photonic crystals. In this paper, we describe the analytical approach in detail, and discuss specific structures and modulation techniques as well as the required steps for achieving complete time reversal. We also show that our scheme is only very weakly sensitive to material losses and dispersion.

We study the third-order spontaneous parametric down-conversion (TOSPDC) process, as a means to generate entangled photon triplets. Specifically, we consider thin optical fibers as the nonlinear medium to be used as the basis for TOSPDC in configurations where phase matching is attained through the use of more than one fiber transverse modes. Our analysis in this paper, which follows from our earlier paper [Opt. Lett. 36, 190–192 (2011)], aims to supply experimentalists with the details required in order to design a TOSPDC photon-triplet source. Specifically, our analysis focuses on the photon triplet state, on the rate of emission, and on the TOSPDC phase-matching characteristics for the cases of frequency-degenerate and frequency nondegenerate TOSPDC.

We theoretically analyze the resonance fluorescence of a solid-state cavity quantum electrodynamics (QED) system that consists of a quantum dot and a cavity. We clarify the effects of pure dephasing by investigating the elastic and inelastic scattering probabilities, the fluorescence power spectrum, and the energy exchange with the environment. Pure dephasing interactions with the environment both enhance nonresonant coupling between the dot and the cavity and enable the pump light to continuously absorb energy from the environment under appropriate conditions.

We present a multiple-scattering method to study the dispersion of multilayer honeycomb arrays of metallic nanoparticles. Three types of stacking are considered. It is shown that the energy spectra for these multilayer photonic structures strongly depend on the distances between the layers, stacking number of layers, and the type of stacking, which are closely analogous to the electronic ones in multilayer graphene. The effects of interlayer coupling on the energy spectra have been demonstrated by exact numerical simulations. Thus, extensive applications of such a phenomenon to design optical devices are anticipated.

Two measurable characteristics of microwave one-mode photon states are discussed: a rotated quadrature distribution (tomogram) and normally and antinormally ordered moments of photon creation and annihilation operators. Extraction of these characteristics from an amplified microwave signal is presented. Relations between the tomogram and the moments are found and can be used as a cross-check of experiments. Formalism of the ordered moments is developed. The state purity and generalized uncertainty relations are considered in terms of moments. Unitary and nonunitary time evolution of moments is obtained in the form of a system of linear differential equations in contrast to partial differential equations for quasidistributions. Time evolution is specified for the cases of a harmonic oscillator and a damped harmonic oscillator which describe noiseless and decoherence processes, respectively.

We study tunable interaction of the resonances in the Mach-Zehnder-Fano interferometers (MZFIs). A discrete Mach-Zehnder interferometer (MZI) with balanced arms supports bound states in the continuum. We demonstrate that doping an impurity in conventional MZIs gives rise to robust high-Q Fano resonances with asymmetric line shapes. By means of the modified Fano-Anderson model and the scattering-matrix approach, we show that the transmission and the intensity spectra of the whole system are very sensitive to both the location and the strength of the impurity. The side-coupled Fano defects induce an interaction with different eigenmodes of the pure MZI loop. We explore this interaction by tuning the parameters of the Fano defects. The observed resonance interaction can be attributed to the Fano-Feshbach resonance. We further provide with a particular physical example of photonic crystal circuit the applicability of our concept.

Light scattering by a periodic atomic array is studied when the atoms couple with the mode of a high-finesse optical resonator and are driven by a laser. When the von-Laue condition is not satisfied, there is no coherent emission into the cavity mode, and the latter is pumped via inelastic scattering processes. We consider this situation and identify conditions for which different nonlinear optical processes can occur. We show that these processes can be controlled by suitably tuning the strength of laser and cavity coupling, the angle between laser and cavity axis, and the array periodicity. We characterize the coherence properties of the light when the system can either operate as degenerate parametric amplifier or as a source of antibunched light. Our study permits us to identify the individual multiphoton components of the nonlinear optical response of the atomic array and the corresponding parameter regimes, thereby in principle allowing one to control the nonlinear optical response of the medium.

Quantum contextuality in systems of identical bosonic particles is explicitly exhibited via the maximum violation of a suitable inequality of Clauser-Horne-Shimony-Holt type. Unlike the approaches considered so far, which make use of single-particle observables, our analysis involves collective observables constructed using multiboson operators. An exemplifying scheme to test this violation with a quantum optical setup is also discussed.

More than ten years ago a first step toward quantum error correction (QEC) was implemented [Phys. Rev. Lett. 81, 2152 (1998)]. The work showed there was sufficient control in nuclear magnetic resonance to implement QEC, and demonstrated that the error rate changed from $\epsilon$ to $\sim {\epsilon }^2$. In the current work we reproduce a similar experiment using control techniques that have been since developed, such as the pulses generated by gradient ascent pulse engineering algorithm. We show that the fidelity of the QEC gate sequence and the comparative advantage of QEC are appreciably improved. This advantage is maintained despite the errors introduced by the additional operations needed to protect the quantum states.

With a ${}^9{\mathrm{Be}}^{+}$ trapped-ion hyperfine-state qubit, we demonstrate an error probability per randomized single-qubit gate of $2.0\left(2\right)\times {10}^{-5}$, below the threshold estimate of ${10}^{-4}$ commonly considered sufficient for fault-tolerant quantum computing. The ${}^9{\mathrm{Be}}^{+}$ ion is trapped above a microfabricated surface-electrode ion trap and is manipulated with microwaves applied to a trap electrode. The achievement of low single-qubit-gate errors is an essential step toward the construction of a scalable quantum computer.

We report observations of photoassociation (PA) spectra near the intercombination line in isotopic mixtures of ultracold ytterbium gases. Several heteronuclear bound states have been found for the excited ${}^{170}$Yb${}^{174}$Yb and ${}^{174}$Yb${}^{176}$Yb molecules. We develop a single-channel mass-scaled interaction model for the excited state molecule which well reproduces the measured bound state energies. This is an important step toward optical control of interactions in mixtures of ultracold ytterbium gases using heteronuclear optical Feshbach resonances. The model developed is applicable in collisions of other similar systems, such as cadmium and mercury.

In this work we study the interaction problem of a Dirac oscillator with gravitational fields produced by topological defects. The energy levels of the relativistic oscillator in the cosmic string and in the cosmic dislocation space-times are sensible to curvature and torsion associated to these defects and are important evidence of the influence of the topology on this system. In the presence of a localized magnetic field the energy levels acquire a term associated with the Aharonov-Bohm effect. We obtain the eigenfunctions and eigenvalues and see that in the nonrelativistic limit some results known in standard quantum mechanics are reached.

We prove, using a method based on map-state duality, lower bounds on entanglement resources needed to deterministically implement a bipartite unitary using separable (SEP) operations, which include LOCC (local operations and classical communication) as a particular case. It is known that the Schmidt rank of an entangled pure state resource cannot be less than the Schmidt rank of the unitary. We prove that if these ranks are equal the resource must be uniformly (maximally) entangled: equal nonzero Schmidt coefficients. Higher rank resources can have less entanglement: we have found numerical examples of Schmidt rank 2 unitaries, which can be deterministically implemented, by either SEP or LOCC, using an entangled resource of two qutrits with less than one ebit of entanglement.

A potential experimental system, based on high-stress stoichiometric silicon nitride (${\mathrm{Si}}_3{\mathrm{N}}_4$), is proposed to generate steady-state optomechanical entanglement at room temperature. In the proposed structure, a nanostring interacts dispersively and reactively with a microdisk cavity via the evanescent field. We study the role of both dispersive and reactive couplings in generating optomechanical entanglement, and show that the room-temperature entanglement can be effectively obtained through the dispersive couplings under the reasonable experimental parameters. In particular, in the limits of high temperature ($T$) and high mechanical quality factor ($Q_m$), we find that the logarithmic entanglement depends only on the ratio $T/Q_m$. This indicates that improvements of the material quantity and structure design may lead to more efficient generation of stationary high-temperature entanglement.