We have measured the absolute double-differential cross sections (DDCSs) for electron emission in ionization of O${}_2$ molecules under the impact of 3.5-MeV/u C${}^{6+}$ ions. The data were collected between 10 and 600 eV, in an angular range of ${30}^{\circ }$ to ${150}^{\circ }$. The single-differential cross sections (SDCSs) in emission angle and electron energy are deduced from the electron DDCS spectra. Also, the total cross section has been obtained from the SDCS spectra. The DDCS spectra as well as the SDCS spectra are compared with continuum distorted-wave eikonal initial-state calculations which employ molecular wave functions built as linear combinations of atomic orbitals. The DDCS ratio i.e. $\sigma {{}_{\mathrm{O}}}_2/2{\sigma }_{\mathrm{O}}$, derived by dividing the experimental DDCS for molecular oxygen with the theoretical DDCS for atomic oxygen, does not show any primary or secondary oscillations arising from Young-type interference, which is apparently in contrast to what has been observed earlier for H${}_2$ and in agreement with the model calculation. Similarly, the forward-backward angular asymmetry increases monotonically with the velocity of the emitted electrons. However, the results on the DDCSs, SDCSs, the asymmetry parameter, and the nonexistence of oscillations are in qualitative agreement with the predictions of the model used.

Since the experimental realization of synthetic gauge fields for neutral atoms, the simulation of topologically nontrivial phases of matter with ultracold atoms has become a major focus of cold-atom experiments. However, several obvious differences exist between cold-atom and solid-state systems, for instance the small size of the atomic cloud and the smooth confining potential. In this article we show that sharp boundaries are not required to realize quantum Hall or quantum spin Hall physics in optical lattices and, on the contrary, that edge states in a smooth confinement exhibit additional interesting properties, such as spatially resolved splitting and merging of bulk bands and the emergence of robust auxiliary states in bulk gaps to preserve the topological quantum numbers. In addition, we numerically validate that these states are robust against disorder. Finally, we analyze possible detection methods, with a focus on Bragg spectroscopy, to demonstrate that the edge states can be detected and that Bragg spectroscopy can reveal how topological edge states are connected to the different bulk bands.

Fano resonance spectroscopy (FRS) is used to investigate the photonic resonance properties of the defect states in two-dimensional finite-sized photonic crystals (PCs). This study examines the scattering cross-section spectra by changing the direction of the incident light continuously. The present FRS is applied to the intrinsic localized defect produced by displacing a single rod atom from its regular site, which creates one defect mode within the first gap and two defect modes within the second gap simultaneously. The present examination has made clear the correlation between the asymmetry of the scattering cross-section spectra—characterized by the so-called Fano $q$ value—and the optical energy flows in the PC, in particular, that the optical incoming flux is maximized for $q^{-1}=0$. This fact demonstrates the presence of the selective capturing of photons at the defect state in the incoming process of light; moreover, it can be recognized merely by knowledge of the $q$ values. The Fano resonances have thus been successfully used to elucidate the resonance nature of the localized defect states in photonic crystals.

The quantum statistical properties of light emitted by a two-photon double Raman laser is investigated. Using the master equation derived in the good-cavity limit, we study the squeezing and entanglement properties of the cavity field. It turns out that the cavity radiation exhibits two-mode squeezing and entanglement in the transient as well as steady state regime for realizable parameters. We establish a connection between two-mode squeezing and entanglement that gives insight into the physical origin of these quantum features. We also discuss the interplay between the laser detuning and amplitude in modifying the properties of the cavity field.

The electronic structure and fragmentation of the hydrofluorocarbon compound 1,1,1,2-tetrafluoroethane (CF${}_3$-CH${}_2$F) were studied using spectroscopical methods and quantum chemical calculations. Valence photoelectron spectra and the ionic fragmentation products were recorded with synchrotron radiation in the vacuum ultraviolet (VUV) region. The geometric and electronic structures of the CF${}_3$-CH${}_2$F molecule were calculated using the complete active space perturbation theory of second order. The calculated vertical ionization energies were used to interpret the experimental photoelectron spectrum. VUV photodissociation of the sample molecule was studied with photoelectron-photoion coincidence spectroscopy. Coincident ion yields are shown for several cations as a function of electron binding energy. The experimental data are discussed in comparison with theory and previous work.

We study the spin-Seebeck effect in a strongly interacting, two-component Fermi gas and propose an experiment to measure this effect by relatively displacing spin-up and spin-down atomic clouds in a trap using spin-dependent temperature gradients. We compute the spin-Seebeck coefficient and related spin-heat transport coefficients as functions of temperature and interaction strength. We find that, when the interspin scattering length becomes larger than the Fermi wavelength, the spin-Seebeck coefficient changes sign as a function of temperature, and hence so does the direction of the spin separation. We compute this zero-crossing temperature as a function of interaction strength and in particular in the unitary limit for the interspin scattering.

The stationary state of a single-atom (single-qubit) laser is shown to be a phase-averaged nonlinear coherent state—an eigenstate of a specific deformed annihilation operator. The solution found for the stationary state is unique and valid for all regimes of the single-qubit laser operation. We have found the parametrization of the deformed annihilation operator which provides superconvergence in finding the stationary state by iteration. It is also shown that, contrary to the case of the usual laser with constant Einstein coefficients describing transition probabilities, for the single-atom laser the interaction-induced transition probabilities effectively depend on the field intensity.

We demonstrate that Casimir-Polder energies between noble gas atoms (dissolved in water) and oil-water interfaces are highly surface specific. Both repulsion (e.g., hexane) and attraction (e.g., glycerine and cyclodecane) is found with different oils. For several intermediate oils (e.g., hexadecane, decane, and cyclohexane) both attraction and repulsion can be found in the same system. Near these oil-water interfaces the interaction is repulsive in the nonretarded limit and turns attractive at larger distances as retardation becomes important. These highly surface specific interactions may have a role to play in biological systems where the surface may be more or less accessible to dissolved atoms.

We propose a scheme to generate four-mode cluster states with four atomic ensembles trapped in single-mode cavities connected by short fibers. With the aid of the cavity dissipation, we find that a four-mode cluster state can be unconditionally created by the simultaneous driving of the ensembles with laser pulses of suitably chosen Rabi frequencies and phases. The scheme could be easily extended to the case of $N$-mode cluster states.

A five-qubit-codeword-stabilized quantum code is implemented in a seven-qubit system using nuclear magnetic resonance. Our experiment implements a good nonadditive quantum code which encodes a larger Hilbert space than any stabilizer code with the same length and capable of correcting the same kind of errors. The experimentally measured quantum coherence is shown to be robust against artificially introduced errors, benchmarking the success in implementing the quantum error correction code. Given the typical decoherence time of the system, our experiment illustrates the ability of coherent control to implement complex quantum circuits for demonstrating interesting results in spin qubits for quantum computing.

The autoionizing resonances ${\left(2s^2\right)}^{1}S$, ${\left(2p^2\right)}^{1}D$, and ${\left(2s2p\right)}^{1}P$ of helium have been investigated employing ejected-electron spectroscopy by fast-electron impact at incident energies of 250–2000 eV and ejected angles of 26°–116°. Shore parameters of the line shapes for these three resonances have been obtained in such high incident energy regime except at 250 eV. Distinct discrepancies between the present results at 250 eV and those of McDonald and Crowe at 200 eV [D. G. McDonald and A. Crowe, J. Phys. B 25, 2129 (1992); D. G. McDonald and A. Crowe, J. Phys. B 25, 4313 (1992)] and Sise et al. at 250 eV [O. Sise, M. Dogan, I. Okur, and A. Crowe, Phys. Rev. A 84, 022705 (2011)], especially for ${}^{1}D$ and ${}^{1}P$ states, are also observed.

We show that, in contrast to immediate intuition, Anderson localization of noninteracting particles induced by a disordered potential in free space can increase (i.e., the localization length can decrease) when the particle energy increases, for appropriately tailored disorder correlations. We predict the effect in one, two, and three dimensions, and propose a simple method to observe it using ultracold atoms placed in optical disorder. The increase of localization with the particle energy can serve to discriminate quantum versus classical localization.

Motivated by a recent experiment [Phys. Rev. Lett. 106, 150401 (2011)], we simulate the collision between two clouds of cold Fermi gas at unitarity conditions by using an extended Thomas-Fermi density functional. At variance with the current interpretation of the experiments, where the role of viscosity is emphasized, we find that a quantitative agreement with the experimental observation of the dynamics of the cloud collisions is obtained within our superfluid effective hydrodynamics approach, where density variations during the collision are controlled by a purely dispersive quantum gradient term. We also suggest different initial conditions where dispersive density ripples can be detected with the available experimental spatial resolution.

We propose an optical scheme to generate a superposition of coherent states with enhanced size adopting an interferometric setting at the single-photon level currently available in the laboratory. Our scheme employs a nondegenerate optical parametric amplifier together with two beam splitters so that the detection of single photons at the output conditionally implements the desired superposition of second-order photonic operations. We analyze our proposed scheme by considering realistic on-off photodetectors with nonideal efficiency in heralding the success of conditional events. A high-quality performance of our scheme is demonstrated in view of various criteria such as quantum fidelity, mean output energy, and measure of quantum interference.

We propose a scheme to generate isolated attosecond (as) pulses by high-peak-power multicycle laser fields which is based on high-order harmonics generation (HHG) from a helium atom irradiated by a three-color femtosecond (fs) laser field. An infrared laser acts as the driving laser and two tunable lasers act as control fields which are used to modulate the ellipticity and amplitude of the driving field respectively. With well-chosen parameters, an isolated 100 as pulse is generated with a duration of 50 fs.

Temperature can be responsible for strengthening effective couplings between quantum states, determining a hierarchy of interactions, and making it possible to establish such dynamical regimes known as Zeno dynamics, wherein a strong coupling can hinder the effects of a weak one. The relevant physical mechanisms which connect the structure of a thermal state with the appearance of special dynamical regimes are analyzed in depth.

We introduce a simple photonic probing scheme of remote nondestructive parity measurement (RNPM) on a pair of matter qubits. The protocol works as a single module for key operations such as entanglement generation, Bell measurement, and parity check measurement, which are sufficient not only for building up a quantum repeater but also for equipping it with entanglement distillation. Moreover, the RNPM protocol can also be used for generating cluster states toward measurement-based quantum computation.

Quantum bit commitment has long been known to be impossible. Nevertheless, just as in the classical case, imposing certain constraints on the power of the parties may enable the construction of asymptotically secure protocols. Here, we introduce a quantum bit commitment protocol and prove that it is asymptotically secure if cheating is restricted to Gaussian operations. This protocol exploits continuous-variable quantum optical carriers, for which such a Gaussian constraint is experimentally relevant as the high optical nonlinearity needed to effect deterministic non-Gaussian cheating is inaccessible.

We present an efficient quantum repeater protocol that uses coupled systems of quantum-dot spins and optical microcavities, in which the spatial entanglement of a photon system can be converted into polarization entanglement of electron spins. The bit-flip and phase-flip errors on the polarization state of each qubit caused by noisy channels can be rejected, without resorting to additional qubits. Two remote parties can obtain the maximally entangled electron-spin state and store it deterministically after the transmission of photons, independent of the noise parameters. The transmission distance of photons will not be limited by the coherence time of memory units in the present protocol, unlike the previous atomic-ensemble-based quantum repeater protocols, and it can be applied directly in long-distance quantum-communication protocols.