Simulations of ion guiding through an insulating cylindrical nanocapillary are performed in continuation of a recent theoretical work [N. Stolterfoht, Phys. Rev. A 87, 012902 (2013)]. The ions are assumed to move on classical trajectories affected by the electric field primarily produced by the charge patch deposited near the capillary entrance. The deposited charges are transported along the capillary wall using a nonlinear conductivity law. Calculations for different capillary tilt angles from 0${}^{\circ }$ to $8{}^{\circ }$ are performed and compared with previous experimental results. The main focus of the analysis is to reveal unknown guiding mechanisms by a detailed investigation of the calculated results. Surprisingly, after reaching a maximum, the field component perpendicular to the capillary axis is found to decrease with increasing charge inserted into the capillary. At equilibrium, this field is nearly constant in all directions of the capillary along the entrance charge patch. The extension of this charge patch increases with increasing tilt angle although a simple picture of undeflected ions predicts the opposite behavior. These unexpected results simplify the theoretical treatment so that analytical expressions could be derived describing essential properties of the ion guiding. In particular, unknown parameters previously introduced in semiempirical models are interpreted.

We report on our investigation of the formation and survival of long-lived Rydberg states in argon produced by pulsed laser excitation of ultracold metastable state argon atoms in a magneto-optical trap. The states studied have a ${}^2{P}_{1/2}$ core. Low angular momentum Rydberg states with this core normally autoionize rapidly. If, however, atoms are excited in the presence of electric fields, higher angular momentum states, traditionally termed “ZEKE states” (ZEKE is derived from “zero kinetic energy”) can be formed. The lifetime of these states can be orders of magnitude greater than low angular momentum states. In this paper, we report on the time dependence of ZEKE Rydberg state population in an ultracold environment.

In this work, we analyze the free expansion of Bose-Einstein condensates containing multicharged vortices. The atomic cloud is initially confined in a three-dimensional asymmetric harmonic trap. We apply both approximate variational solutions and numerical simulations of the Gross-Pitaevskii equation. The data obtained provide a way to establish the presence as well as the multiplicity of vortices based only on the properties of the expanded cloud which can be obtained via time-of-flight measurements. In addition, several features such as the evolution of the vortex core size and the asymptotic velocity during free expansion were studied considering the atomic cloud as being released from different harmonic trap configurations.

We show that topological vortex pumping can be implemented for a dilute Bose-Einstein condensate confined in a magnetic time-averaged orbiting potential trap with axial optical confinement. Contrary to earlier proposals for the vortex pump, we do not employ an additional optical potential to trap the condensate in the radial direction, but instead, the radial confinement is provided by the magnetic field throughout the pumping cycle. By performing numerical simulations based on the spin-1 Gross-Pitaevskii equation, we find that several pumping cycles can be carried out to produce a highly charged vortex before a majority of the particles escape from the trap or before the vortex splits into singly charged vortices. On the other hand, we observe that an additional, relatively weak optical plug potential is efficient in preventing splitting and reducing particle loss. With these results, we hope to bring the vortex pump closer to experimental realization.

We study correlation effects and excitations in a dipolar Bose gas bilayer which is modeled by a one-dimensional double-well trap that determines the width of an individual layer, the distance between the two layers, and the height of the barrier between them. For the ground-state calculations we use the hypernetted-chain Euler-Lagrange method, and for the calculation of the excitations we use the correlated basis function method. We observe instabilities both for wide, well-separated layers dominated by intralayer attraction of the dipoles, and for narrow layers that are close to each other dominated by interlayer attraction. The behavior of the pair distribution function leads to the interpretation that the monomer phase becomes unstable when pairing of two dipoles becomes energetically favorable between or within layers, respectively. In both cases we observe a tendency towards “rotonization,” i.e., the appearance of a soft mode with finite momentum in the excitation spectrum. The dynamic structure function is not simply characterized by a single excitation mode but has a nontrivial multipeak structure that is not captured by the Bijl-Feynman approximation. The dipole-dipole interaction between different layers leads to additional damping compared to the damping obtained for uncoupled layers.

We investigate, both analytically and numerically, the quasisuperfluidity properties of periodic Bose-Einstein condensates (BECs) in a quasi-one-dimensional (1D) ring with optical lattices (OL) of different kinds (linear and nonlinear) and with a moving defect of an infinite mass inside. To study the dynamics of the condensate we used a mean-field approximation describing the condensate by use of the Gross-Pitaevskii equation for the order parameter. We show that the resonant scattering of sound Bloch waves with the defect profoundly affect BEC superfluidity. In particular, a moving defect always leads to the breakdown of superfluidity independently of the value of its velocity. For weak periodic potentials the superfluidity breakdown may occur on a very long time scale (quasisuperfluidity) but the breakdown process can be accelerated by increasing the strength of the OL. Quite remarkably, we find that when the length of the ring is small enough to imply the discreteness of the reciprocal space, it becomes possible to avoid the resonant scattering and to restore quasi-superfluidity.

We describe progress toward a precise measurement of the recoil energy of an atom measured using a modified grating-echo atom interferometer (AI) that involves three standing-wave (sw) pulses. With this technique, an additional sw pulse is used to shift the phase of excited momentum states, which produces a modulation in the contrast of the interference pattern. The signal exhibits narrow fringes that revive periodically at twice the two-photon recoil frequency, $2{\omega }_q$, as a function of the onset time of the pulse. Experiments are performed using samples of laser-cooled rubidium atoms with temperatures $\lesssim$5 $\mu$K in a nonmagnetic apparatus. We demonstrate a measurement of ${\omega }_q$ with a statistical uncertainty of 37 parts per ${10}^9$ (ppb) on a time scale of $\sim$45 ms in 14 h. Further statistical improvements are anticipated by extending this time scale and narrowing the signal fringe width. However, the total systematic uncertainty is estimated to be $\sim$6 parts per ${10}^6$ (ppm). We describe methods of reducing these systematic errors.

In this paper, we propose a resource-optimal linear-optical scheme for quantum nondemolition detection of single-photon presence. By measuring the state of ancillary photons, the presence of a photon in signal mode is revealed with a success probability of 1/2 without any disturbance to its state. We also show how to tune the setup to perform quantum nondemolition measurement of the signal photon state, and we provide a tradeoff between the extracted information and the signal state disturbance. Moreover, the optimality of resources and methods by which to increase the success probability are discussed.

The generalized rotating-wave approximation with counter-rotating interactions has been applied to a biased qubit-oscillator system. Analytical expressions are explicitly given for all eigenvalues and eigenstates. For a flux qubit coupled to superconducting oscillators, spectra calculated by our approach are in excellent agreement with experiment. Calculated energy levels for a variety of biases also agree well with those obtained via exact diagonalization for a wide range of coupling strengths. Dynamics of the qubit has also been examined, and results lend further support to the validity of the analytical approximation employed here. Our approach can be readily implemented and applied to superconducting qubit-oscillator experiments conducted currently and in the near future with a biased qubit and for all accessible coupling strengths.

We present an all-optical incoherent control of superluminal propagation of a 3 ns laser pulse. The experimental results show an induced advance up to 400 ps, without significant distortion, continuously controlled by the characteristics of a control pulse. The measurements agree with numerical simulation.

In this paper, we propose two quantum optomechanical arrangements that permit the dissipation-enabled generation of steady two-mode mechanical squeezed states. In the first setup, the mechanical oscillators are placed in a two-mode optical resonator while in the second setup the mechanical oscillators are located in two coupled single-mode cavities. We show analytically that for an appropriate choice of the pump parameters, the two mechanical oscillators can be driven by cavity dissipation into a stationary two-mode squeezed vacuum, provided that mechanical damping is negligible. The effect of thermal fluctuations is also investigated in detail and shows that ground-state precooling of the oscillators is not necessary for the two-mode squeezing. These proposals can be realized in a number of optomechanical systems with current state-of-the-art experimental techniques.

We present a theoretical investigation of stimulated emission pumping to achieve sub-diffraction-limited spatial resolution in coherent anti-Stokes Raman scattering (CARS) microscopy. A pair of control light fields is used to prepopulate the Raman state involved in the CARS process prior to the CARS signal generation. Efficient prepopulation is achieved by employing a path via an electronic or vibrational state. Thereby, the buildup of a coherence between the ground and Raman state during irradiation by the light fields for CARS signal generation is prevented, resulting in the suppression of the CARS intensity by more than 99.8$\%$. Two-dimensional spatial excitation profiles have been calculated using donut-shaped spatial profiles for the control light fields, thus, an intensity-dependent narrowing of the CARS excitation profiles below the diffraction limit. Using computer-generated test images we demonstrate a resolution beyond the diffraction limit for CARS microscopy, which is scalable by the control light field intensity, similar to stimulated emission depletion microscopy.

We show that nonradiative interactions between atomic dipoles placed in a waveguide can give rise to deterministic entanglement at ranges much larger than their resonant wavelength. The range increases as the dipole resonance approaches the waveguide's cutoff frequency, caused by the giant density of photon modes near cutoff, a regime where the standard (perturbative) Markov approximation fails. We provide analytical theories for both the Markovian and non-Markovian regimes, supported by numerical simulations, and discuss possible experimental realizations.

The Gottesman-Knill theorem allows for the efficient simulation of stabilizer-based quantum error-correction circuits. Errors in these circuits are commonly modeled as depolarizing channels by using Monte Carlo methods to insert Pauli gates randomly throughout the circuit. Although convenient, these channels are poor approximations of common, realistic channels such as amplitude damping. Here we analyze a larger set of efficiently simulable error channels by allowing the random insertion of any one-qubit gate or measurement that can be efficiently simulated within the stabilizer formalism. Our error channels are shown to be a viable method for accurately approximating realistic error channels.

We propose a realizable and efficient approach for exciting long-range ion-pair molecules, known as heavy Rydberg states, in an ultracold ${}^{85}$Rb gas via Feshbach resonances. Heavy Rydberg states, the molecular analogs of electronic Rydberg states, with the electron replaced by an atomic anion, offer opportunities for novel physics, including the formation of ultracold anions and strongly coupled plasmas. We map the positions, lifetimes, and Franck-Condon factors of heavy Rydberg resonances across a wide range of excitation energies, and we calculate the rates of formation for the most promising transitions through long-lived intermediate interferometric resonances.

The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase was first predicted in two-dimensional superconductors about 50 years ago, but so far unambiguous experimental evidence is still lacking. The recently experimentally realized spin-imbalanced Fermi gases may potentially unveil this elusive state, but they require very stringent experimental conditions. In this Rapid Communication, we show that FFLO phases may be observed even in a three-dimensional (3D) degenerate Fermi gas with spin-orbit coupling and an in-plane Zeeman field. The FFLO phase is driven by the interplay between the asymmetry of the Fermi surface and the superfluid order, instead of the interplay between magnetic and superconducting order in solid materials. The predicted FFLO phase exists in a giant parameter region, possesses a stable long-range superfluid order due to the 3D geometry, and can be observed with an experimentally already achieved temperature ($T\sim 0.05E_F$), thus opening a fascinating avenue for exploring FFLO physics.

We analyze the symmetries in an open quantum system composed by three coupled and detuned harmonic oscillators in the presence of a common heat bath. It is shown analytically how to engineer the couplings and frequencies of the system so as to have several degrees of freedom unaffected by decoherence, irrespective of the specific spectral density or initial state of the bath. This partial thermalization allows observing asymptotic entanglement at moderate temperatures, even in the nonresonant case. This latter feature cannot be seen in the simpler situation of only two oscillators, highlighting the richer structural variety of the three-body case. When departing from the strict conditions for partial thermalization, a hierarchical structure of dissipation rates for the normal modes is observed, leading to a long transient where quantum correlations such as the quantum discord are largely preserved, as well as to synchronous dynamics of the oscillators quadratures.