We study theoretically how excitations due to spontaneous emission and trap fluctuations combine with elastic collisions to change the momentum distribution of a trapped nondegenerate one-dimensional (1D) Bose gas. Using calculated collisional relaxation rates, we first present a semianalytical model for the momentum distribution evolution to get insight into the main processes responsible for the system dynamics. We then present a Monte Carlo simulation that includes features that cannot be handled analytically and compare its results to experimental data. These calculations provide a baseline for how 1D Bose gases evolve due to heating processes in the absence of diffractive collisions that might thermalize the gases.

We consider a trapped atomic ensemble of interacting bosons in the presence of a single trapped ion in a quasi-one-dimensional geometry. Our study is carried out by means of the newly developed multilayer-multiconfiguration time-dependent Hartree method for bosons, a numerical exact approach to simulate quantum many-body dynamics. In particular, we are interested in the scenario by which the ion is so strongly trapped that its motion can be effectively neglected. This enables us to focus on the atomic ensemble only. With the development of a model potential for the atom-ion interaction, we are able to numerically obtain the exact many-body ground state of the atomic ensemble in the presence of an ion. We analyze the influence of the atom number and the atom-atom interaction on the ground-state properties. Interestingly, for weakly interacting atoms, we find that the ion impedes the transition from the ideal gas behavior to the Thomas-Fermi limit. Furthermore, we show that this effect can be exploited to infer the presence of the ion both in the momentum distribution of the atomic cloud and by observing the interference fringes occurring during an expansion of the quantum gas. In the strong interacting regime, the ion modifies the fragmentation process in dependence of the atom number parity which allows a clear identification of the latter in expansion experiments. Hence, we propose in both regimes experimentally viable strategies to assess the impact of the ion on the many-body state of the atomic gas. This study serves as the first building block for systematically investigating the many-body physics of such hybrid system.

We study the ground-state phase diagram of two-dimensional two-component (or pseudospin-$\frac{1}{2}$) Bose gases in mutually antiparallel synthetic magnetic fields in the space of the total filling factor and the ratio of the intercomponent coupling $g_{\uparrow \downarrow }$ to the intracomponent coupling $g>0$. This time-reversal-invariant setting represents a bosonic analog of spin Hall systems. Using exact diagonalization, we find that (fractional) quantum spin Hall states composed of a pair of nearly independent quantum Hall states are remarkably robust and persist for $g_{\uparrow \downarrow }$ up to as large as $g$. For $g_{\uparrow \downarrow }=-g$, we find the exact many-body ground state in which particles in different spin states form pairs. This gives the exact critical line beyond which the system collapses in the thermodynamic limit.

Does the Abraham or the Minkowski momentum describe the momentum transport of light in media? Here we show that this is a question of fluid dynamics. In momentum transport, neither the Abraham nor the Minkowski momentum is fundamental, but they emerge depending on the fluid-mechanical response of the medium on the light. If the fluid is not brought into motion, the Minkowski momentum emerges, if it moves the Abraham momentum appears.

We demonstrate control over the acceleration of two-dimensional Airy beams propagating in optically induced photonic lattices. Depending on the lattice strength, we observe a slowing-down and suppression of the self-acceleration of Airy beams, as well as a formation of discrete lattice beams. Moreover, we explore the effects of different artificial single-side defects on the propagation and acceleration. For positive defects, the localization of the Airy beam to the defect site is further enhanced, while for negative defects most of the power is repelled from this site.

Non-conventional emission of light, comprising engaged rotating light cogs, is measured and analyzed. The source of this unique emission is an array of coupled surface emitting lasers, each emitting an optical vortex. The complex rotating light structures are formed spontaneously by specific combinations of the individual vortices, each carrying two types of “charge”: orbital angular momentum (±1 topological charge) and a relative engagement phase (0 or π). These charges determine the specific form in which the individual rotating fields are engaged to generate the emanated light gear. The experimentally observed formations and dynamic evolution of the light gears stem from the complex nonlinear dynamics of the coupled rotating-field emitters, a mechanism which we have successfully modeled and utilized for interpreting the obtained results. The engaged light gears can be used in controlled generation and transmission of multiple degrees of freedom photons, for high-bit-rate classic and quantum telecommunications, particle manipulation, and super-resolution imaging.

We study the dynamics of disentanglement of two qubits initially prepared in a Bell state and coupled at different sites to an Ising spin chain in a transverse field (ITF) playing the role of a dynamic spin environment. The initial state of the whole system is prepared in a tensor product state ${\rho }_{\mathrm{Bell}}\otimes {\rho }_{\mathrm{chain}}$, where the state of the chain is taken to be given by the ground state $\left|G\right({\lambda }_i)\rangle$ of the ITF Hamiltonian $H_E\left({\lambda }_i\right)$ with an initial field ${\lambda }_i$. At time $t=0^{+}$, the strength of the transverse field is suddenly quenched to a new value, ${\lambda }_f$, and the whole system (chain $+$ qubits) undergoes a unitary dynamics generated by the total Hamiltonian $H_{\mathrm{Tot}}=H_E\left({\lambda }_f\right)+H_I$, where $H_I$ describes a local interaction between the qubits and the spin chain. The resulting dynamics leads to a disentanglement of the qubits, which is described through Wootters' concurrence, due to their interaction with the nonequilibrium environment. The concurrence is related to the Loschmidt echo, which in turn is expressed in terms of the time-dependent covariance matrix associated with the ITF. This permits a precise numerical and analytical analysis of the disentanglement dynamics of the qubits as a function of their distance, bath properties, and quench amplitude. In particular, we emphasize the special role played by a critical initial environment.

In this paper we investigate the capability of quantum routing (quantum state fusion) to implement two useful quantum communications protocols. The analyzed protocols include quantum authentication of quantum messages and nondestructive linear-optical Bell-state manipulation. We also present the concept of quantum decoupler—a device implementing an inverse operation to quantum routing. We demonstrate that both quantum router and decoupler can work as specialized disentangling gates.

The absolute single-photoionization cross section was measured for Cl-like ${\mathrm{K}}^{2+}$ over the photon energy range from 44.2 to 69.7 eV at a constant energy resolution of 0.045 eV. The experiments were performed by merging an ion beam with a beam of synchrotron radiation from an undulator. The ground-state ionization threshold was measured at 0.004-eV energy resolution to be $45.717\pm 0.030$ eV. The measurements are rich in resonance structure due to multiple Rydberg series of transitions to autoionizing states. These series are assigned spectroscopically using the quantum defect method, guided by pseudorelativistic Hartree-Fock calculations for the energies and oscillator strengths of transitions to autoionizing states. The experimental results, which include significant contributions from ${\mathrm{K}}^{2+}$ ions initially in metastable states, are in satisfactory agreement with a linear superposition of semirelativistic R-matrix calculations of photoionization cross sections from these initial states.

We theoretically investigate the behavior of a system of fermionic atoms loaded in a bipartite one-dimensional optical lattice that is under the action of an external time-periodic driving force. By using Floquet theory, an effective model is derived. The bare hopping coefficients are renormalized by zeroth-order Bessel functions of the first kind with different arguments for the nearest-neighbor and next-nearest-neighbor hopping. The insulating behavior characterizing the system at half filling in the absence of driving is dynamically suppressed, and for particular values of the driving parameter the system becomes either a standard metal or an unconventional metal with four Fermi points. The existence of the four-Fermi-point metal relies on the fact that, as a consequence of the shaking procedure, the next-nearest-neighbor hopping coefficients become significant compared to the nearest-neighbor ones. We use the bosonization technique to investigate the effect of on-site Hubbard interactions on the four-Fermi-point metal-insulator phase transition. Attractive interactions are expected to enlarge the regime of parameters where the unconventional metallic phase arises, whereas repulsive interactions reduce it. This metallic phase is known to be a Luther-Emery liquid (spin-gapped metal) for both repulsive and attractive interactions, contrary to the usual Hubbard model, which exhibits a Mott-insulator phase for repulsive interactions. Ultracold fermions in driven one-dimensional bipartite optical lattices provide an interesting platform for the realization of this long-studied four-Fermi-point unconventional metal.

We investigate the many-body Landau-Zener (LZ) process in a two-site Bose-Hubbard model driven by a time-periodic field. We find that the driving field may induce sideband transitions in addition to the main LZ transitions. These photon-induced sideband transitions are a signature of the photon-assisted tunneling in our many-body LZ process. In the Rabi regime, where the system is dominated by the intermode coupling, the system can be looked as an ensemble of identical noninteracting single-particle LZ systems and the photon-induced sideband transitions are similar to the ones in single-particle LZ systems. In the Fock regime, where the system is dominated by the interparticle interaction, we develop an analytical theory for understanding the sideband transitions, which is confirmed by our numerical simulation. Furthermore, we discuss the quantization of the driving field. In the effective model of the quantized driving field, the sideband transitions can be understood as the LZ transitions between states of different “photon” numbers.

We describe a method to generate a synthetic gauge potential for ultracold atoms held in an optical lattice. Our approach uses a time-periodic driving potential based on quickly alternating two Hamiltonians to engineer the appropriate Aharonov-Bohm phases, and permits the simulation of a uniform tunable magnetic field. We explicitly demonstrate that our split-driving scheme reproduces the behavior of a charged quantum particle in a magnetic field over the complete range of field strengths, and obtain the Hofstadter butterfly band structure for the Floquet quasienergies.

When quantum systems are shifted faster than their transition and coupling time scales, their susceptibility is dramatically modified. We measure the optical susceptibility of a strongly modulated electromagnetically induced transparency system. Time vs detuning plots for different pump modulation frequencies reveal a transition between an adiabatic regime where a series of smooth pulses are created and a nonadiabatic regime where a strong transient oscillating response is added. Applying a magnetic field lifts the hyperfine level degeneracy, revealing an interference effect between the different magnetic level transients. We explore the dynamics of the magnetic and nonmagnetic cases and discuss their coherent nature. We finally combine the global phase of the transmitted pulses with the transient interference to achieve broadband magnetic sensing without losing the sensitivity of a single electromagnetically induced transparency line.

Vector-field electron tomography (VFET) reconstructs electromagnetic vector fields of magnetic nanomaterials using transmission electron microscopy. The theory behind this reconstruction process is well established, but the practical implications of experimental errors and how they affect the accuracy of the reconstructed vector fields is not well understood, hindering progress in the use of these techniques for routine magnetic characterization of nanomaterials. Here, we present an analysis of the propagation of stochastic errors through a VFET algorithm. A method for determining the contribution of image noise to errors in a reconstructed vector potential is derived. Simulations are performed to test the validity of this method when applied to shot noise, which shows good agreement with theory.

We present an efficient scheme for generation of an isolated attosecond (as) pulse based on the combination of two well-known methods: polarization gating method plus a method based on using two colors ($\omega +\omega /2$). The first uses a pulse whose ellipticity is small within a very short time interval (called a polarization gating). By adding a second pulse whose frequency is a half-frequency (midinfrared) of the first pulse, we extend significantly the cutoff frequency, as well as the width of the supercontinuum harmonic spectrum. The high-order harmonic generation is calculated using the strong-field approximation theory. As a result, an isolated 42-as pulse is generated directly by superposing the hundreds of harmonics. To explain the mechanism of the ultrashort attosecond generation, we perform the semiclassical three-step model simulation and wavelet time-frequency transform of the harmonic spectra.

Fermionic linear optics is a model of quantum computation which is efficiently simulable on a classical probabilistic computer. We study the problem of a classical simulation of fermionic linear optics augmented with noisy auxiliary states. If the auxiliary state can be expressed as a convex combination of pure fermionic Gaussian states, the corresponding computation scheme is classically simulable. We present an analytic characterization of the set of convex-Gaussian states in the first nontrivial case, in which the Hilbert space of the ancilla is a four-mode Fock space. We use our result to solve an open problem recently posed by de Melo et al. [New J. Phys. 15, 013015 (2013)] and to study in detail the geometrical properties of the set of convex-Gaussian states.

Localized radiation sources are analyzed with respect to the relation of nonclassicality and quantum entanglement of the emitted light. The source field parts of the radiation emitted in different directions are closely related to each other. As a consequence, nonclassicality of the light fields in one direction directly implies entanglement of the field modes in different directions. This implication can be extended to multipartite entanglement and multitime quantum correlations. Given that a nonclassical effect is observed, our approach explicitly yields the multipartite entanglement witnesses. Two examples are considered, the fluorescence radiation of a system of two-level atoms and of excitons in a semiconductor quantum well.

We present theoretical three-dimensional fully differential cross sections (FDCSs) for electron-impact excitation-ionization of helium when the ionized electron is found outside of the scattering plane. Using our first Born approximation model, we examine the effects of electron correlation in the initial state and show that it significantly affects the shape of the out-of-plane FDCS.

We show that waveform-synthesized chirped laser fields are efficient tools for coherent harmonic control. A single harmonic order, or two harmonic orders, can be selectively enhanced by using a two-color field allowing a moderate linear chirp for each color. Different harmonic orders within a wide spectral range can be selectively enhanced by adjusting the laser parameters. Our theory bridges two current harmonic control techniques, namely, single-color phase shaping and multicolor amplitude synthesis, and opens the door to new harmonic control possibilities.

We develop a quantum model for nonequilibrium Bose-Einstein condensation of photons and polaritons in planar microcavity devices. The model builds on laser theory and includes the spatial dynamics of the cavity field, a saturation mechanism, and some frequency dependence of the gain: quantum Langevin equations are written for a cavity field coupled to a continuous distribution of externally pumped two-level emitters with a well-defined frequency. As an example of application, the method is used to study the linearized quantum fluctuations around a steady-state condensed state. In the good-cavity regime, an effective equation for the cavity field only is proposed in terms of a stochastic Gross-Pitaevskii equation. Perspectives in view of a full quantum simulation of the nonequilibrium condensation process are finally sketched.