The response of highly excited potassium Rydberg states with $n$ $\sim 305$ to a sinusoidal electric drive field in the radio frequency (100–300 MHz) regime is examined by photoexcitation from the $4s$ ground state using a uv probe beam. The drive field couples many Rydberg levels simultaneously and results in a coherent response that leads to a variety of multiphoton processes. The excitation spectra are analyzed within the framework of Floquet theory and reveal signatures of quantum optical phenomena such as electromagnetically induced transparency and Autler-Townes splitting seen with few-level systems.

Vortices are found in a fermion system with repulsive dipole-dipole interactions, trapped by a rotating quasi-two-dimensional harmonic oscillator potential. Such systems have much in common with electrons in quantum dots, where rotation is induced via an external magnetic field. In contrast to the Coulomb interactions between electrons, the (externally tunable) anisotropy of the dipole-dipole interaction breaks the rotational symmetry of the Hamiltonian. This may cause the otherwise rotationally symmetric exact wave function to reveal its internal structure more directly.

We investigate the behavior of the anomalous correlation function in two-dimensional Bose gas. In the local case, we find that this quantity has a finite value in the limit of weak interactions at zero temperature. The effects of the anomalous density on some thermodynamic quantities are also considered. These effects can modify, in particular, the chemical potential, the ground-state energy, the depletion, and the superfluid fraction. Our predictions are in good agreement with recent analytical and numerical calculations. We show also that the anomalous density presents a significant importance compared to the noncondensed one at zero temperature. The single-particle anomalous correlation function is expressed in two-dimensional homogenous Bose gases by using the density-phase fluctuation. We then confirm that the anomalous average accompanies in analogous manner the true condensate at zero temperature, while it does not exist at finite temperature.

For two-dimensional (2D) atomic Fermi gases in harmonic traps, the SO(2,1) symmetry is broken by the interatomic interaction explicitly via the contact correlation operator. Consequently, the frequency of the breathing mode ${\omega }_B$ of the 2D Fermi gas can be different from $2{\omega }_0$, with ${\omega }_0$ the trapping frequency of harmonic potentials. At zero temperature, we use the sum rules of density correlation functions to yield upper bounds for ${\omega }_B$. We further calculate ${\omega }_B$ through the Euler equations in the hydrodynamic regime. The obtained value of ${\omega }_B$ satisfies the upper bounds and shows deviation from $2{\omega }_0$, which can be as large as about $8\%$.

We numerically study the expansion dynamics of ultracold atoms in a one-dimensional disordered potential in the presence of a weak position measurement of the atoms. We specifically consider this position measurement to be realized by a combination of an external laser and a periodic array of optical microcavities along a waveguide. The position information is acquired through the scattering of a near-resonant laser photon into a specific eigenmode of one of the cavities. The time evolution of the atomic density in the presence of this light-scattering mechanism is described within a Lindblad master equation approach, which is numerically implemented using the Monte Carlo wave function technique. We find that an arbitrarily weak rate of photon emission leads to a breakdown of Anderson localization of the atoms.

We study the existence, stability, and dynamics of multivortex discrete solitons in a centrally coupled ring of nonlinear waveguides. A detailed analysis of possible geometrical configurations of globally linked elementary vortices within a stationary state is presented, together with the studies of their linear stability and perturbed dynamics. We identify regimes with robust switching between different vortex configurations, induced via the coordinated flipping of all vortex charges in a cluster, adiabatic spiraling of vortex lines, or spontaneous decay of unstable vortex clusters into stable solitons. These three mechanisms allow for all-optical switching between six topologically distinct vortex configurations.

We propose a potentially practical scheme for creating macroscopic entangled coherent states (ECSs) between two distant ensembles of polar molecules (PMs) placed, respectively, in separate transmission-line resonators (TLRs) interconnected by a superconducting charge qubit. The ECS between two PM ensembles can be generated in the dispersive regime through control of the superconducting qubit under classical strong-driving conditions, during which the TLRs are only virtually excited. The tunable coupling of the TLR hybrid system provides us the potential of extending the ECS generation to multimode cases. The experimental feasibility of the scheme is discussed briefly based on currently available techniques.

The physics of interacting Fibonacci anyons can be studied with strongly interacting Rydberg atoms in a lattice, when due to the dipole blockade the simultaneous laser excitation of adjacent atoms is forbidden. The Hilbert space maps then directly on the fusion space of Fibonacci anyons. Interactions between anyons are generated and controlled by the intensity and frequency of the excitation laser. Fusion outcomes of neighboring anyons can be determined experimentally via the measurement of three-point correlations among three consecutive atoms. Our work shows that a Rydberg lattice gas constitutes a natural physical platform for the experimental exploration of topological quantum liquids of non-Abelian anyons.

Uncertainty relations capture the essence of the inevitable randomness associated with the outcomes of two incompatible quantum measurements. Recently, Berta et al. [Nature Phys. 6, 659 (2010)] have shown that the lower bound on the uncertainties of the measurement outcomes depends on the correlations between the observed system and an observer who possesses a quantum memory. If the system is maximally entangled with its memory, the outcomes of two incompatible measurements made on the system can be predicted precisely. Here, we obtain an uncertainty relation that tightens the lower bound of Berta et al. by incorporating an additional term that depends on the quantum discord and the classical correlations of the joint state of the observed system and the quantum memory. We discuss several examples of states for which our lower bound is tighter than the bound of Berta et al. On the application side, we discuss the relevance of our inequality for the security of quantum key distribution and show that it can be used to provide bounds on the distillable common randomness and the entanglement of formation of bipartite quantum states.

We propose a measure of nonclassical correlations in bipartite quantum states based on local unitary operations. We prove that the measure is nonzero if and only if the quantum discord is nonzero; this is achieved via a new characterization of zero discord states in terms of the state's correlation matrix. Moreover, our scheme can be extended to ensure that the same relationship holds even with a generalized version of quantum discord in which higher-rank projective measurements are allowed. We next derive a closed-form expression for our scheme in the cases of Werner states and $(2\times N)$-dimensional systems. The latter reveals that for $(2\times N)$-dimensional states, our measure reduces to the geometric discord [Dakić et al., Phys. Rev. Lett. 105, 190502 (2010)]. A connection to the Clauser-Horne-Shimony-Holt inequality is shown. We close with a characterization of all maximally nonclassical, yet separable, $(2\times N)$-dimensional states of rank at most 2 (with respect to our measure).

Time-local master equations are more generally applicable than is often recognized, but at first sight, it would seem that they can only safely be used in time intervals where the time evolution is invertible. Using the Jaynes-Cummings model, we here construct an explicit example where two different Hamiltonians, corresponding to two different noninvertible and non-Markovian time evolutions, lead to arbitrarily similar time-local master equations. This illustrates how the time-local master equation, on its own in this case, does not uniquely determine the time evolution. The example is, nevertheless, artificial in the sense that a rapid change in (at least) one of the Hamiltonians is needed. The change must also occur at a very specific instance in time. If a Hamiltonian is known not to have such very specific behavior but is “physically well behaved,” then one may conjecture that a time-local master equation also determines the time evolution when it is not invertible.

Although nonclassical quantum states are important both conceptually and as a resource for quantum technology, it is often difficult to test whether a given quantum system displays nonclassicality. A simple method to certify nonclassicality is introduced, based on easily accessible collective atomic quadrature measurements, without the need of full state tomography. The statistics is analyzed beyond the ground-state noise level by direct sampling of a regularized atomic quadrature quasiprobability. Nonclassicality of a squeezed ensemble of $2\times {10}^5$ cesium atoms is demonstrated, with a significance of up to 23 standard deviations.

Quantum walks constitute important tools in different applications, especially in quantum algorithms. To a great extent their usefulness is due to unusual diffusive features, allowing much faster spreading than their classical counterparts. Such behavior, although frequently credited to intrinsic quantum interference, usually is not completely characterized. Using a recently developed Green's function approach [Phys. Rev. A 84, 042343 (2011)], we describe here—in a rather general way—the problem dynamics in terms of a true Feynman sum-over-paths history. This allows one to explicitly identify interference effects and also to explain the emergence of superdiffusivity. The present analysis has the potential to help in designing quantum walks with distinct transport properties.

Measurements of extreme ultraviolet radiation from highly charged gadolinium ions were made at the National Institute of Standards and Technology. The ions were produced and confined in an electron-beam ion trap (EBIT), and the spectra were recorded with a flat-field grazing-incidence spectrometer in the wavelength range 3–17 nm. Ionization stages from Rb-like to Cu-like gadolinium were selected by tuning the electron-beam energies between 0.97 and 1.7 keV. Strong intrashell $n=4$–$n=4$ transitions were identified by performing detailed collisional-radiative modeling of the EBIT plasma. A total of 73 spectral features were recorded, including 59 new identifications.

A semianalytical approach to atomic waveguide scattering for harmonic confinement is developed, taking into account all partial waves. As a consequence $\ell$-wave confinement-induced resonances are formed, being coupled to each other due to the confinement. The corresponding resonance condition is obtained analytically using the $K$-matrix formalism. Atomic scattering is described by transition diagrams which depict all relevant processes the atoms undergo during the collision. Our analytical results are compared to corresponding numerical data and show very good agreement.

The influence of a high-intensity laser field on the Coulomb explosion and stopping power for a swift C${}_{60}$ cluster ion in a plasma target is studied by means of the molecular dynamics method based on the linearized Vlasov-Poisson theory. In the presence of the laser field, the general expressions for the induced potential in the target among the ions within the cluster are derived. Based on the numerical solution of the equations of motion for the constituent ions, the Coulomb explosion patterns and the cluster's stopping power are discussed for a range of laser and plasma parameters. Numerical results show that the laser field affects the correlation between the ions and contributes to weakening the wake effect and the stopping power as compared to the laser-free case. On the other hand, the vicinage effects in the cluster Coulomb explosion dynamics and the stopping power are strongly affected by the variations in the laser parameters, cluster speed, and plasma parameters. For example, Coulomb explosions are found to be hindered in the longitudinal expansion with the increasing of laser intensity and laser angle, and the Coulomb explosions proceed faster for lower plasma densities and higher electron temperatures.

We observe long-lived tightly bound van der Waals molecules of ytterbium in a three-dimensional optical lattice with a lifetime of 8.0 s. The molecules, state-selectively produced by a photoassociation technique from a Bose-Einstein condensate or an atomic Mott insulator, are successfully detected with a photodissociation method where the molecules are photodissociated into two atoms and the atoms are captured by a magneto-optical trap or optical molasses, for the fluorescence detection. This work will open up various possibilities of research with van der Waals molecules in an optical lattice.

We experimentally and numerically study the atomic response and pulse propagation effects of high-order harmonics generated in Xe, Kr, and Ar driven by a 2.1-μm infrared femtosecond light source. The light source is an optical parametric chirped-pulse amplifier, and a modified strong-field approximation and three-dimensional pulse propagation code are used for the numerical simulations. The extended cutoff in the long-wavelength-driven high-order harmonic generation has revealed the spectral shaping of high-order harmonics due to the atomic structure (or photorecombination cross section) and the macroscopic effects, which are the main factors of determining the conversion efficiency besides the driving wavelength. Using precise numerical simulations to determine the macroscopic electron wave packet, we are able to extract the photorecombination cross sections from experimental high-order harmonic spectra in the presence of macroscopic effects. We have experimentally observed that the macroscopic effects shift the observed Cooper minimum of Kr from 80 eV to 60–70 eV and wash out the Cooper minimum of Ar. Measured high-harmonic conversion efficiencies per harmonic near the cutoff are ∼10${}^{-9}$ for all three gases.

Data are presented on the wall-induced nuclear spin-relaxation rate of ${}^{129}$Xe in glass cells in which the interior walls are coated with either rubidium hydride (RbH) or rubidium deuteride (RbD). The relaxation rates have been measured as a function of both magnetic field $(0.08<B<1.0\text{T})$ and temperature $(205<T<323\text{K})$. Spin relaxation was observed to decrease significantly with increasing magnetic field in both RbH- and RbD-coated cells at all temperatures studied. At temperatures above roughly 250 K, there is strong evidence that relaxation is due to long-range dipolar interactions with paramagnetic sites.

We present here a microscopic analysis of the cooperative light scattering on an atomic system consisting of $\Lambda$-type configured atoms with the spin-degenerate ground state. The results are compared with a similar system consisting of standard “two-level” atoms of the Dicke model. We discuss advantages of the considered system in context of its possible implications for light storage in a macroscopic ensemble of dense and ultracold atoms.