We present a general method to detect nonclassical radiation fields with systems of on-off detectors. We especially study higher order correlations for the identification of nonclassical radiation. This allows us to directly characterize quantum correlations by the statistics measured with systems of on-off detectors. Additionally, we generalize our method to multiple detector systems for measurements of correlations between light fields. We also consider multimode radiation fields and isolate nonclassicality in terms of the space time correlations. Finally, we present results for the quantum statistics using on-off detectors operating in nonlinear detection modes.

The recent paper by Ziauddin and Qamar [Phys. Rev. A 85, 055804 (2012)] proposes control of the Goos-Hänchen shift of a Gaussian field incident on a cavity containing duplicated two-level atoms. This control relies on phase control of the optical response of the intracavity medium that has been demonstrated earlier [Phys. Rev. Lett. 101, 213601 (2008)]. We show that the authors make an incorrect use of the results of this latter paper.

The concept behind using a Gaussian-shaped probe beam to control the Goos-Hänchen shift using a duplicated two-level atomic medium inside a cavity [Phys. Rev. A 85, 055804 (2012)] is presented. It is obvious from the analysis that by using certain approximations, the required conditions can be imposed on the probe field corresponding to the Gaussian-shaped incident beam and control field driving the intracavity atomic medium.

Topological code is a stabilizer quantum error correcting code whose generators are local but logical operators are topologically nontrivial and nonlocal. It offers interesting features such as the homological deformations of string operators and anyonic excitations on it. Topological codes are also closely related to the “topological order,” which has been an important concept in condensed-matter physics. In this paper, we consider continuous-variable versions of topological codes, including the toric code by Kitaev [A. Y. Kitaev, Ann. Phys. 303, 2 (2003)] with a single type of stabilizer on the checkerboard lattice, and the color code by Bombin and Martin-Delgado [H. Bombin and M. A. Martin-Delgado, Phys. Rev. Lett. 97, 180501 (2006)]. We show that it is possible to consider continuous-variable analog of these topological codes.

We report the experimentally determined $KLL$ dielectronic-recombination (DR) resonance strengths of Li- to O-like gold. The measurement was performed with an electron beam ion trap, and the x rays emitted from DR and radiative recombination (RR) were both observed. The DR resonance strengths were determined by normalizing DR x-ray intensities to the theoretical RR cross sections. The experimental DR resonance strengths are compared with the theoretical ones, and the comparison shows a good agreement. The scaling laws of the $KLL$ DR resonance strengths were obtained as a function of atomic number for B-like and C-like ions by fitting the present and existing experimental results.

We investigate second- and third-harmonic generation in a slab of material that displays plasma resonances at the pump and its harmonic frequencies. Near-zero refractive indices and local field enhancement can deplete the pump for kW/cm${}^2$ incident powers, without resorting to other resonant photonic mechanisms. We show that low-threshold, highly efficient nonlinear processes are possible in the presence of losses and phase mismatch in structures that are 10${}^4$ times shorter than typical nonlinear crystals, for relatively low irradiance values.

The spatiotemporal dynamics of singly resonant optical parametric oscillators with external seeding displays hexagonal, roll, and honeycomb patterns, optical turbulence, rogue waves, and cavity solitons. We derive appropriate mean-field equations with a sinc${}^2$ nonlinearity and demonstrate that off-resonance seeding is necessary and responsible for the formation of complex spatial structures via self-organization. We compare this model with those derived close to the threshold of signal generation and find that back-conversion of signal and idler photons is responsible for multiple regions of spatiotemporal self-organization when increasing the power of the pump field.

The spontaneous radiation pattern is calculated for two coaxial disks of atoms, separated by a distance $L$. The atoms are modeled as having $J=0$ ground states and $J=1$ excited states. At $t=0$ the atoms in one disk are excited to their $m=1$ excited-state sublevels, while the atoms in the second disk can be either in their ground or excited states. The manner in which the atoms in each disk modify the radiation pattern of the atoms in the other disk is described. It is shown, for example, that when the atoms in the second disk are in their ground states, they can still lead to an increase in the signal radiated by the first disk in certain directions. The dependence on the Fresnel number of the radiation pattern is calculated. Moreover, it is shown that analytic expressions can be obtained for the radiation pattern if the disks are replaced by Gaussian density distributions.

We present measurements of the Faraday and the Cotton-Mouton effects of helium gas at $\lambda =1064$ nm. Our apparatus is based on an up-to-date resonant optical cavity coupled to longitudinal and transverse magnetic fields. This cavity increases the signal to be measured by more than a factor of 270 000 compared to the one acquired after a single passage of light in the magnetic field region. We have reached a precision of a few percent for both the Faraday and the Cotton-Mouton effect. Our measurements give the experimental value of the Faraday effect at $\lambda =1064$ nm. This value is compatible with the theoretical prediction. Concerning the Cotton-Mouton effect, our measurement agrees at better than 1$\sigma$ with theoretical predictions.

We study the dynamics of a system composed of two coupled cavities, each interacting with a single Rydberg atom. The interplay between Rydberg-Rydberg interaction and photon hopping enables the transition of the atoms from the collective ground state to the double Rydberg excitation state by individually interacting with the optical normal modes and suppressing the upconversion process between them. The atomic transition is accompanied by the two-photon absorption and emission of the normal modes. Since the energy level structure of the atom-cavity system is photon number dependent there is only a pair of states being in the two-photon resonance. Therefore, the system can act as a quantum nonlinear absorption filter through the nonclassical quantum process, converting coherent light field into a nonclassical state. Meanwhile, the vacuum field in the cavity inspires the Rydberg atoms to simultaneously emit two photons into the normal mode, resulting in obvious emission enhancement of the mode.

We address the forces exerted by the random electromagnetic field emitted by a fluctuating optical source on a kind of dielectric nanoparticles that have arisen much interest because of their recently shown magnetodielectric behavior. The illumination with light, or other electromagnetic wave, of a given state of coherence allows us to create photonic forces, a particular case of which are optical analogous to the Casimir-Polder and van der Waals forces, as well as of thermal forces out of thermodynamic equilibrium. This leads to a deeper understanding of the conditions and limitations under which some theories of these forces were established. We also study the effects of the coherence length and of sharp changes in the particle differential scattering cross section due to Kerker minimum forward or zero backward conditions. We show how the nanoparticle Mie resonances, constituted by the induced electric and magnetic dipoles, lead to long distance attractions to the source, as well as to the possible predominance of magnetic forces. In addition, it is shown how, by manipulating the fluctuating source, either pushing or tractor beams are obtained, even in the far zone. These effects are specially relevant when quasimonochromatic emission is employed, and manifest the possibility of performing a monitoring of these mechanical interactions, in particular by a photonic analogy of those aforementioned classical thermal forces. This opens paths to nanoparticle ensembling and manipulation. The influence of the excitation of surface waves of the source is also considered.

We introduce and discuss a set of tunable two-mode states of continuous-variable systems, as well as a simple, effective scheme for their experimental generation. This class of tunable entangled resources is defined by a general ansatz depending on two experimentally adjustable parameters. It is very ample and flexible as it encompasses Gaussian as well as non-Gaussian states. The latter include, among others, known states such as squeezed number states and de-Gaussified photon-added and photon-subtracted squeezed states, the latter being the most efficient non-Gaussian resources currently available in the laboratory. Moreover, it contains the classes of squeezed Bell states and even more general non-Gaussian resources that can be optimized according to the specific quantum technological task that needs to be realized. The proposed experimental scheme exploits linear optical operations and photon detections performed on a pair of uncorrelated two-mode Gaussian squeezed states. The desired non-Gaussian state is then realized via ancillary squeezing and conditioning. Two independent, freely tunable experimental parameters can be exploited to generate different states and to optimize the performance in implementing a given quantum protocol. As a concrete instance, we analyze in detail the performance of different states considered as resources for the realization of quantum teleportation in realistic conditions. For the fidelity of teleportation of an unknown coherent state, we show that the resources associated with the optimized parameters outperform, in a significant range of experimental values, both Gaussian twin beams and photon-subtracted squeezed states.

We use laser light near resonant with a molecular bound-to-bound transition to control a magnetic Feshbach resonance in ultracold Fermi gases of ${}^{40}$K atoms. The spectrum of excited molecular states is measured by applying a laser field that couples the ground Feshbach molecular state to electronically excited molecular states. Nine strong bound-to-bound resonances are observed below the ${}^2{P}_{1/2}+{}^2{S}_{1/2}$ threshold. We use radio-frequency spectroscopy to characterize the laser-dressed bound state near a specific bound-to-bound resonance and show clearly the shift of the magnetic Feshbach resonance using light. The demonstrated technology could be used to modify interatomic interactions with high spatial and temporal resolutions in the crossover regime from a Bose-Einstein condensate to a Bardeen-Cooper-Schrieffer superfluid.

For a quantum system of $N$ identical, harmonically interacting particles in a one-dimensional harmonic trap we calculate for the bosonic and fermionic ground state the corresponding one-particle reduced density operator ${\widehat{\rho }}_1$ analytically. In case of bosons ${\widehat{\rho }}_1$ is a Gibbs state for an effective harmonic oscillator. Hence the natural orbitals are Hermite functions and their occupation numbers obey a Boltzmann distribution. Intriguingly, for fermions with not too large couplings the natural orbitals coincide up to just a small error with the bosonic ones. In case of strong coupling this still holds qualitatively. Moreover, the decay of the decreasingly ordered fermionic natural occupation numbers is given by the bosonic one, but modified by an algebraic prefactor. Significant differences to bosons occur only for the largest occupation numbers. After all, the “gap” at the “Fermi level” decreases with increasing coupling strength but remains well pronounced even for strong interaction.

Interpretations of an experiment on the backaction in a weak measurement in [Iinuma et al., New J. Phys. 13, 033041 (2011)] are revisited. We show two different but essentially equivalent interpretations for this experiment along the original scenario of weak measurements proposed by Aharonov, Albert, and Vaidman [Phys. Rev. Lett. 60, 1351 (1988)]. To do this, we introduce the notion of extended weak values, which is associated not only with the states of the system but also the state of the measuring device. We also evaluate fluctuations in this experiment, and found that an optimal measurement strength exists for a fixed polarization angle prepared as an initial state, at which fluctuations in measurement results vanish. The consistency of this evaluation with the experimental results is discussed.

A connection is established between the non-Abelian phases obtained via adiabatic driving and those acquired via quantum Zeno dynamics induced by repeated projective measurements. In comparison to the adiabatic case, the Zeno dynamics is shown to be more flexible in tuning the system evolution, which paves the way for the implementation of unitary quantum gates and applications in quantum control.

The generation and the characterization of multipartite entangled light is an important and challenging task in quantum optics. In this paper the entanglement properties of the light emitted from a planar semiconductor microcavity are studied. The intracavity scattering dynamics leads to the emission of light that is described by a four-partite $W$ state. Its multipartite correlations are identified by using the method of entanglement witnesses. Entanglement conditions are derived, which are based on a general witness constructed from $W$ states. The results can be used to detect entanglement of light that propagates through lossy and even turbulent media.

The energies and geometry of the ${}^{24}$Mg-He${}_2$ and ${}^{40}$Ca-He${}_2$ triatomic complexes are studied using the hyperspherical coupled-channel method. With pairwise He-$X$ (where $X$ denotes Mg or Ca) potentials, we find that the ${}^{24}$Mg-${}^4$He${}_2$ and ${}^{24}$Mg-${}^3$He-${}^4$He systems possess two bound states and the ${}^{24}$Mg-${}^3$He${}_2$ system possesses one, while the ${}^{40}$Ca-${}^4$He${}_2$, ${}^{40}$Ca-${}^3$He${}_2$, and ${}^{40}$Ca-${}^3$He-${}^4$He systems are found to support four, three, and three bound states, respectively. The different energies and geometric behaviors are reported when the He atom changes from ${}^3$He to ${}^4$He for the He-He-${}^{24}$Mg (${}^{40}$Ca) isotopic combinations. We also study structures of excited states and find that for some excited states, they are quite different from the ground states.

Density-functional theory (DFT) is an exact alternative formulation of quantum mechanics, in which it is possible to calculate the total energy, the spin, and the charge density of many-electron systems in the ground state. In practice, it is necessary to use uncontrolled approximations that can mainly be verified against experimental data. Atoms and ions are simple systems, where the approximations of DFT can be easily tested. We have calculated within DFT the total energies, spin, and higher ionization energies of all the ions of elements with $1⩽Z⩽29$. We find the calculations in close agreement with experiment, with an error of typically less than ca. 1% for $1⩽Z⩽29$. Surprisingly, the error depends on the electronic configuration of the ion in both local spin density approximation and Perdew-Burke-Ernzerhof general gradient approximation and independent of both self-interaction correction and relativistic corrections. Larger errors are found for systems in which the spin-spin correlation is significant, which indicates the possible benefit from an orbital-dependent formulation of the correlation energy functional.