We study the generation of angular momentum carrying states for a single cold particle by breaking the symmetry of a spatial adiabatic passage process in a two-dimensional system consisting of three harmonic potential wells. By following a superposition of two eigenstates of the system, a single cold particle is completely transferred to the degenerate first excited states of the final trap, which are resonantly coupled via tunneling to the ground states of the initial and middle traps. Depending on the total time of the process, angular momentum is generated in the final trap, with values that oscillate between $\pm \hslash$. This process is discussed in terms of the asymptotic eigenstates of the individual wells and the results are checked by simulations of the full two-dimensional Schrödinger equation.

Recently, concepts of topological phases of matter are extended to nonequilibrium systems, especially periodically driven systems. In this paper, we construct an example which shows nonequilibrium topological phase transitions using ultracold fermions in optical lattices. We show that the Rabi oscillation has the possibility to induce nonequilibrium topological phases which are classified into time-reversal-invariant topological insulators for a two-orbital model of alkaline-earth-metal atoms. Furthermore, we study the nonequilibrium topological phases using time-dependent Schrieffer–Wolff-type perturbation theory, and we obtain an analytical expression to describe the topological phase transitions from a high-frequency limit of external driving fields.

We investigate nonlinear effects in an electromechanical system consisting of a superconducting charge qubit coupled to a transmission line resonator and a nanomechanical oscillator, which in turn is coupled to another transmission line resonator. The nonlinearities induced by the superconducting qubit and the optomechanical coupling play an important role in creating optomechanical entanglement as well as the squeezing of the transmitted microwave field. We show that strong squeezing of the microwave field and robust optomechanical entanglement can be achieved in the presence of moderate thermal decoherence of the mechanical mode. We also discuss the effect of the coupling of the superconducting qubit to the nanomechanical oscillator on the bistability behavior of the mean photon number.

Spatial field correlation functions represent a key quantity for the description of mesoscopic phenomena in disordered media and the optical characterization of complex materials. Yet many aspects related to the vector nature of light waves have not been investigated so far. We study theoretically the polarization and coherence properties of electromagnetic waves produced by a dipole source in a three-dimensional uncorrelated disordered medium. The spatial field correlation matrix is calculated analytically using a multiple-scattering theory for polarized light. This allows us to provide a formal description of the light depolarization process in terms of “polarization eigenchannels” and to derive analytical formulas for the spatial coherence of multiply scattered light.

Paraxial propagation theories are not suitable for describing the behavior of electromagnetic wave fields in any states of spatial coherence and polarization in the microdiffraction domain. The proposed nonparaxial theory overcomes such limitations by modeling (i) any planar source in terms of sets of point sources with tensor statistical behavior, and (ii) the transport of the wave field on scalar, deterministic, time-independent, and nonparaxial propagation modes, defined only by the geometry of the boundary conditions of the experimental setups. So the field emission by the source and the space structure due to the modes are independent from each other. The theory provides a unified framework for the power and the states of spatial coherence and polarization of the field, as well as for interference and diffraction, and describes the significant changes suffered by the wave fields in the microdiffraction domain.

We study coherent and incoherent interactions between a discrete vortex soliton and a discrete fundamental soliton in two-dimensional photonic lattices, which present a scheme for all-optical routings and topological transformations of vorticities. Due to the multilobe intensity and π/2-phase delay between each two lobes of the discrete vortex soliton, the coherent soliton interactions allow both solitons to evolve into localized states with a single lobe on multiple different possible destination ports, which depend on the initial phase of the discrete fundamental soliton. We show that charge flippings of phase singularities and orbital angular momentum transfer can occur during the coherent interactions between the two solitons. For incoherent interactions, by controlling the relative powers of the two solitons, we reveal that soliton steering can be realized by either attracting the discrete fundamental soliton to four ports or localizing the four-lobe discrete vortex soliton into a ring soliton.

We address a recently established inequality $\mathcal{P}\ge \mathcal{I}$ that constrains the degrees of polarization $\mathcal{P}$ and indistinguishability $\mathcal{I}$. We derive said inequality within three different frameworks, discussing its respective physical meaning. We show that in its original formulation the inequality involved a single degree of freedom, and that only by entangling polarization and path (momentum) in laboratory space, can such an inequality represent a constraint between these degrees of freedom. We show how this could be done with the help of a Mach-Zehnder-like array. We discuss this multipurpose device, which can be employed to address several issues of current interest, such as tests of the complementarity principle, partial coherence stemming from unobserved degrees of freedom, geometric phases of entangled states evolving on the Schmidt sphere, etc. Besides its experimental feasibility, the proposed device serves as a tool for studying common features of quantum and classical entangled states. In particular, it serves for testing a newly proposed measure of coherence, called Bell's measure, using experimental techniques that are independent of those already employed.

The question of the transfer of angular momentum from light to objects is a key issue in optical tweezers and thus raises issues in physics, chemistry, and biology. Most of the attempts have been performed either with spin angular momentum using light's polarization or using orbital angular momentum with twisted beams. We experimentally demonstrate here the exchange of angular momentum from a linearly polarized plane wave to a two dimensional asymmetric object. More precisely, we show that the diffracted light from a snail-shaped mask carries local orbital angular momentum whose topological charge depends on the symmetry of the object. This opens the way to a means to produce micrometer-sized twisted beams from a high power laser or even pulsed beams.

Finite-size effects for blackbody radiation in a cavity are revealed. We find out simple scaling laws for thermodynamic functions of blackbody radiation in a finite cavity of arbitrary shape and predict the anisotropy of blackbody radiation pressure in asymmetric cavities. Special thermodynamic effects accompanying cavities merge are discussed.

In a recent publication [Galley, Phys. Rev. Lett. 110, 174301 (2013)], Galley proposed an initial value problem formulation of Hamilton's principle that enables consideration of dissipative systems. Here we explore this formulation at the level of field theories with infinite degrees of freedom. In particular, we illustrate that it affords a previously unwarranted and appealing as well as broadly relevant possibility, namely, to generalize the popular collective coordinate or variational method to open systems, i.e., nonconservative ones. To showcase the relevance or validity of the method we explore two case examples from the timely area of $\mathcal{PT}$-symmetric variants of field theories, in this case for a sine-Gordon and for a ${\varphi }^4$ model.

We investigate the reduction in the probability of single-photon emission from a single-emitter system caused by intersystem crossing. The physical model is that a single-emitter system with three levels is excited by a square pulse laser, and then a single photon is emitted at a controllable time. We find that the intersystem crossing always reduces the probability of single-photon emission. We obtain quantitative and analytical expressions for the probabilities of zero-, one-, and two-photon emission and Mandel's Q parameter as the function of the intersystem crossing rate under the conditions of finite field strength and finite interaction time with the laser pulse. We discuss the conditions for obtaining the maximal probability of single-photon emission in the presence of intersystem crossing. We find that one can obtain a high probability of single-photon emission from the single-emitter system using square pulse excitation in comparison with continuous wave excitation. Mandel's Q parameter exhibits a transition from a sub-Poissonian behavior to a super-Poissonian behavior due to the influence of intersystem crossing. The calculated Mandel's Q parameter and second-order correlation function of photon emission considering the coherent effect are in better agreement with the experimental data.

Recently, it was shown that a nonzero transverse angular momentum manifests itself in a polarization-dependent intensity shift of the barycenter of a paraxial light beam [Aiello et al., Phys. Rev. Lett. 103, 100401 (2009)]. The underlying effect is phenomenologically similar to the spin Hall effect of light but does not depend on the specific light-matter interaction and can be interpreted as a purely geometric effect. Thus, it was named the geometric spin Hall effect of light. Here, we experimentally investigate the appearance of this effect in tightly focused vector beams. We use an experimental nanoprobing technique in combination with a reconstruction algorithm to verify the relative shifts of the components of the electric energy density and the shift of the intensity in the focal plane. By that, we experimentally demonstrate the geometric spin Hall effect of light in a highly nonparaxial beam.

The high-resolution x-ray-scattering technique is used to study the elastic scattering of atoms and molecules in the gas phase. The elastic squared form factor, which is the square of the Fourier transformation of the electron density distribution in position space and reveals the pure electronic structure of atoms and molecules in the ground state, of molecular hydrogen is measured at an incident photon energy of about 9889 eV and an energy resolution of about 70 meV. Although it is generally thought that the x-ray-scattering technique is identical to high-energy electron scattering, at least for elastic scattering these two techniques have an apparent difference, i.e., the pure electronic structure of a molecule in the ground state can be determined by x-ray scattering while it cannot be obtained by the high-energy electron impact method due to the interference between the scattering of separate nuclei and of the electrons in the target. The present experimental results match the theoretical calculations very well, which demonstrates that high-resolution x-ray scattering is a powerful tool to study the electronic structure of atoms and molecules in the ground state.

We experimentally settle the three-decades-old question of whether or not promethiumlike heavy ions have strong resonance lines in hot plasmas. In 1980, Curtis and Ellis [Phys. Rev. Lett. 45, 2099 (1980)] predicted that promethiumlike heavy ions should have an alkali-metal structure with a ground-state configuration of $4f^{14}5s$, and should exhibit strong $5s\text{−}5p$ resonance lines in hot plasmas. However, after many experimental efforts, no clear indication of the predicted resonance lines was found. The work presented herein resolves this question by clearly showing that the predicted resonance lines for bismuth are negligibly weak because of the presence of the ${\left[4f^{13}5s^2\right]}_{7/2}$ metastable state, even though the ground-state configuration is $4f^{14}5s$, as predicted. To obtain these results, we used an electron-beam ion trap that made it possible to exploit a fine-tuned charge-state distribution, and analyzed the experimental spectra with collisional-radiative model calculations.

We present a density matrix approach for computing global solutions of Hartree-Fock theory, based on semidefinite programming (SDP), that gives upper and lower bounds on the Hartree-Fock energy of quantum systems. Equality of the upper- and lower-bound energies guarantees that the computed solution is the globally optimal solution of Hartree-Fock theory. For strongly correlated systems the SDP approach provides an alternative to the locally optimized Hartree-Fock energies and densities from the standard solution of the Euler-Lagrange equations. Applications are made to the potential energy curves of the H${}_4$ dimer and the N${}_2$ molecule.

We demonstrate experimentally a scheme to measure small temporal delays, much smaller than the pulse width, between optical pulses. Specifically, we observe an interference effect, based on the concepts of quantum weak measurements and weak value amplification, through which a sub-pulse-width temporal delay between two femtosecond pulses induces a measurable shift of the central frequency of the pulse. The amount of frequency shift, and the accompanying losses of the measurement, can be tailored by postselecting different states of polarization. Our scheme requires only spectrum measurements and linear optics elements, hence greatly facilitating its implementation. Thus it appears to be a promising technique for measuring small and rapidly varying temporal delays.

We study the electron-positron pair-creation process from the vacuum under a very strong electric field. The external field is so strong that discrete states can dive into the negative energy continuum (the Dirac sea). This process is simultaneously associated with the onset of pair creation as well as the possibility for capturing the created electrons. By varying the total spatial width of the potential well, we can shift these trapping states in and out of the negative energy continuum while keeping the associated electric force the same. We compute the population transfer in and out of these states by solving the corresponding quantum field theoretical equations for the field operator on a space-time grid. We compare the population of these states obtained by projecting the time-evolved states on instantaneous energy eigenstates with the kinetic-energy spectrum of the ejected positrons.

We report on a bright, nondegenerate type-I parametric down-conversion source, which is well suited for passive decoy-state quantum key distribution. We show the photon-number-resolved analysis over a broad range of pump powers and we prove heralded higher-order $n$-photon states up to $n=4$. The inferred photon click statistics exhibit excellent agreements to the theoretical predictions. From our measurement results we conclude that our source meets the requirements to avert photon-number-splitting attacks.

We analyze theoretically the decoherence of two interacting electrons in a double self-assembled quantum dot due to a random telegraph noise. For this purpose we have examined the pure dephasing rate by evaluating the decoherence factor. The latter has been shown to be different from that calculated within the Gaussian approximation in the strong coupling regime. In order to determine the influence of the random telegraph noise on the entanglement of the system states, the concurrence, the populations, and the entropy are evaluated as well. Our results show that telegraph noise can severely impact the coherence of charge qubits.