The violation of the Svetlichny’s inequality (SI) [Phys. Rev. D 35, 3066 (1987)] is sufficient but not necessary for genuine tripartite nonlocal correlations. Here we quantify the relationship between tripartite entanglement and the maximum expectation value of the Svetlichny operator (which is bounded from above by the inequality) for the two inequivalent subclasses of pure three-qubit states: the Greenberger-Horne-Zeilinger (GHZ) class and the $W$ class. We show that the maximum for the GHZ-class states reduces to Mermin’s inequality [Phys. Rev. Lett. 65, 1838 (1990)] modulo a constant factor, and although it is a function of the three tangle and the residual concurrence, large numbers of states do not violate the inequality. We further show that by design SI is more suitable as a measure of genuine tripartite nonlocality between the three qubits in the $W$-class states, and the maximum is a certain function of the bipartite entanglement (the concurrence) of the three reduced states, and only when their sum attains a certain threshold value do they violate the inequality.

A one-electron qubit would offer a new option for quantum information science, including the possibility of extremely long coherence times. One-quantum cyclotron transitions and spin flips have been observed for a single electron in a cylindrical Penning trap. However, an electron suspended in a planar Penning trap is a more promising building block for the array of coupled qubits needed for quantum information studies. The optimized design configurations identified here promise to make it possible to realize the elusive goal of one trapped electron in a planar Penning trap—a substantial step toward a one-electron qubit.

The first ionization potential (IP) of technetium (Tc) has been determined by evaluating Rydberg convergences toward the first ionization potential as well as toward two low-lying excited states of the singly charged Tc ion. The Rydberg states were excited and detected by applying multiphoton resonance ionization mass spectrometry (RIMS) on the long-lived isotope ${}^{99g}$Tc using a three-color excitation scheme. The observed Rydberg convergences yield a result for the first ionization potential of Tc $V_{\mathrm{IP}}(\mathrm{Tc})=7.119380(32)$ eV. This precise value for $V_{\mathrm{IP}}(\mathrm{Tc})$ is somewhat lower than the so far published data of $7.23$ eV or $7.28$ eV, dating back to the 1950s.

We used the relativistic distorted-wave approximation to calculate the excitation of Ar from its ground-state $3p^6$ configuration to the higher lying fine-structure levels of the $3p$${}^5$$3d$, $3p$${}^5$$5s$, and $3p$${}^5$$5p$ manifolds. The calculation has been performed with relativistic Dirac-Fock multiconfiguration wave functions for the ground and excited states. Results for the differential and integrated cross sections are obtained at energies in the range up to 100 eV, and these are compared with available experimental measurements and earlier theoretical nonrelativistic distorted-wave and $R$-matrix calculations. Analytic fits to our integrated cross sections are provided.

Coherent radiation spectrum from high energy $e^{\pm }$ in a bent crystal with arbitrary curvature distribution along the longitudinal coordinate is evaluated, based on the stationary phase approximation. For a uniformly bent crystal a closed-form expression for the spectrum is derived. The spectrum features include a dip at its beginning and the sharp end, which may split into two breaks depending on the particle incidence angle. Estimates of nondipole radiation and multiple scattering effects are given. The value for the crystal bending angle at which the dipole coherent bremsstrahlung theory holds best appears to be $~{10}^{-4}\hspace{0.5em}\mathrm{rad}$.

We report on the observation of nonlinear Faraday rotation with cold atoms at a temperature of $~100$ $\mu$K. The observed nonlinear rotation of the light polarization plane is up to $0.1$ rad over the $1$-mm-size atomic cloud in approximately $10$-mG magnetic field. The nonlinearity of rotation results from long-lived coherence of ground-state Zeeman sublevels created by a near-resonant light. The method allows for creation, detection, and control of atomic superposition states. It also allows applications for precision magnetometry with high spatial and temporal resolution.

We consider the fate of the Dirac points in the spectrum of a honeycomb optical lattice in the presence of a harmonic confining potential. By numerically solving the tight binding model, we calculate the density of states and find that the energy dependence can be understood from analytical arguments. In addition, we show that the density of states of the harmonically trapped lattice system can be understood by application of a local density approximation based on the density of states in the homogeneous lattice. The Dirac points are found to survive locally in the trap as evidenced by the local density of states. Furthermore, they give rise to a distinct spatial profile of a noninteracting Fermi gas.

We employ the hysteretic behavior of a superconducting thin film in the remanent state to generate different traps and flexible magnetic potentials for ultracold atoms. The trap geometry can be programed by externally applied fields. This approach for atom optics is demonstrated by three different trap types realized on a single microstructure: a Z-type trap, a double trap, and a bias-field-free trap. Our studies show that superconductors in the remanent state provide a versatile platform for atom optics and applications in ultracold quantum gases.

We study the establishment of vortex entanglement in remote Bose-Einstein condensates (BECs). We consider a two-mode photonic resource entangled in its orbital angular momentum (OAM) degree of freedom and, by exploiting the process of light-to-BEC OAM transfer, demonstrate that such entanglement can be efficiently passed to the matterlike systems. Our proposal thus represents a building block for novel dissipation-free and long-memory communication channels based on OAM. We discuss issues of practical realizability, stressing the feasibility of our scheme, and present an operative technique for the indirect inference of the set vortex entanglement.

We study a mixture of one-dimensional bosons and spinless fermions at incommensurate filling using phenomenological bosonization and Green’s function techniques. We derive the relation between the parameters of the microscopic Hamiltonian and macroscopic observables. Galilean invariance results in extra constraints for the current-current interactions. We obtain the exact exponents for the various response functions, and show that superfluid fluctuations are enhanced by the effective boson-fermion density-density interaction and suppressed by the effective boson-fermion current-current interaction. In the case of a bosonized model with purely density-density interaction, when the effective boson-fermion density-density interaction is weak enough, the superfluid exponent of the bosons has a nonmonotonic variation with the ratio of the fermion velocity to the boson velocity. In contrast, the density-wave exponent and the exponent for fermionic superfluidity are monotonic functions of the velocity ratio.

We excite the lowest-lying quadrupole mode of a Bose-Einstein condensate by modulating the atomic scattering length via a Feshbach resonance. Excitation occurs at various modulation frequencies, and resonances located at the natural quadrupole frequency of the condensate and at the first harmonic are observed. We also investigate the amplitude of the excited mode as a function of modulation depth. Numerical simulations based on a variational calculation agree with our experimental results and provide insight into the observed behavior.

We perform variational Monte Carlo calculations to show that bosons in a rotating optical lattice will form analogs of fractional quantum Hall states when the tunneling is sufficiently weak compared to the interactions, and the deviation of density from an integer is commensurate with the effective magnetic field. We compare the energies of superfluid and correlated states to one another and to the energies found in full configuration-interaction calculations on small systems. We look at overlaps between our variational states and the exact ground state, characterizing the ways in which fractional quantum Hall effect correlations manifest themselves near the Mott insulating state. We explore the experimental signatures of these states.

We propose a method for the generation of a large variety of entangled states, encoded in the polarization degrees of freedom of $N$ photons, within the same experimental setup. Starting with uncorrelated photons, emitted from $N$ arbitrary single-photon sources, and using linear optical tools only, we demonstrate the creation of all symmetric states (e.g., GHZ and $W$ states), as well as all symmetric and nonsymmetric total angular momentum eigenstates of the $N$-qubit compound.

The interaction of a two-level atomic ensemble with a quantized single-mode electromagnetic field in the presence of optical collisions is investigated both theoretically and experimentally. The main focus is on achieving thermal equilibrium for coupled atom-light states (in particular dressed states). We propose a model of atomic dressed-state thermalization that accounts for the evolution of the pseudo-spin Bloch vector components and characterize the essential role of the spontaneous emission rate in the thermalization process. Our model shows that the time of thermalization of the coupled atom-light states depends strictly on the ratio of the detuning to the resonant Rabi frequency. The predicted time of thermalization is in the nanosecond domain at full optical power and about 10 times shorter than the natural lifetime in our experiment. Experimentally we investigate the interaction of the optical field with rubidium atoms in an ultrahigh-pressure buffer gas cell under the conditions of large atom-field detuning comparable to the thermal energy in frequency units. In particular, an observed asymmetry of the saturated lineshape is interpreted as evidence of thermal equilibrium of coupled atom-light states.

The emission of radiation by a linearly oscillating electric dipole is drastically altered when the dipole is close to the surface of a mirror. The energy is not emitted along optical rays, as for a free dipole, but as a set of four optical vortices. The field lines of energy flow spiral around a set of two lines through the dipole. At a larger distance from the dipole, singularities and isolated vortices appear. It is shown that these interference vortices are due to the vanishing of the magnetic field at their centers. In the plane of the mirror there is a singular circle with a diameter which is proportional to the distance between the dipole and the mirror. Inside this circle, all energy flows to a singularity on the mirror surface.

We introduce infinite range exterior complex scaling (irECS) which provides for complete absorption of outgoing flux in numerical solutions of the time-dependent Schrödinger equation with strong infrared fields. This is demonstrated by computing high harmonic spectra and wave-function overlaps with the exact solution for a one-dimensional model system and by three-dimensional calculations for the H atom and an Ne atom model. We lay out the key ingredients for correct implementation and identify criteria for efficient discretization.

The high harmonic generation from asymmetric molecules with an $\omega +2\omega /3$ multicycle bichromatic laser pulse has been investigated. It is shown that the ionization asymmetry in consecutive half optical cycles for asymmetric molecules is further enhanced since the $2\omega /3$ control laser pulse further enhances the amplitude of the ionization peak at the center of the laser pulse. The $2\omega /3$ control laser pulse also significantly enlarges the difference of the photon energies emitted from the ejected electron in the half optical cycle at the central laser pulse and its next half optical cycle. In addition, a broadband supercontinuum is produced in the plateau of the spectrum, from which an isolated 90-as pulse can be directly obtained.

A master equation approach to the study of environmental effects in the adiabatic population transfer in three-state systems is presented. A systematic comparison with the non-Hermitian Hamiltonian approach [Vitanov and Stenholm, Phys. Rev. A 56, 1463 (1997)] shows that, in the weak-coupling limit, the two treatments lead to essentially the same results. In contrast, in the strong-damping limit the predictions are quite different: In particular, the counterintuitive sequences in the STIRAP scheme turn out to be much more efficient than expected before. This point is explained in terms of quantum Zeno dynamics.

We propose a scheme for quantum nondemolition measurement of photon holes based on electromagnetically induced transparency, which allows direct nondestructive detection of the photon holes. We analyze a scheme based on interaction of a photon hole signal and a coherent probe field with a three-level atomic medium. Using recent advances in electromagnetically induced transparency technology, we show that the measurement is nondestructive for very weak photon hole signals.

We propose an efficient quantum repeater architecture with mesoscopic atomic ensembles, where the Rydberg blockade is employed for deterministic local entanglement generation, entanglement swapping, and entanglement purification. Compared to a conventional atomic-ensemble-based quantum repeater, the entanglement distribution rate is improved by up to two orders of magnitude with the help of the deterministic Rydberg gate. This quantum repeater scheme is robust and fast, and thus opens up a way for practical long-distance quantum communication.