Rm Rb Research Articles

Laser-Assisted Field Evaporation of (R = Gd, Sm) High-Temperature Superconducting Coated Conductors

Abstract In the field of high-temperature superconductors, atom probe tomography is a relatively new instrument, with the ability to provide a new perspective on the 3D nanoscale microstructure. However, field evaporation of nonmetallic materials is fraught with unique challenges that matter little in the world of metallic evaporation. In this study, we review the laser absorption, correlated evaporation, molecular dissociation, and the crystallographic effects on the field evaporation of 800-m (R = Gd, Sm) coated conductor tapes deposited by Reactive Co-Evaporation Cyclic Deposition and Reaction (RCE-CDR). Ultraviolet 355 nm laser pulsing was found to have a substantial beneficial effect on minimizing the fracture probability compared with 532 nm illumination, especially when evaporating insulating oxide precipitates. This, in turn, allows for the 3D compositional analysis of defects such as flux pinning centers introduced by precipitation and doping. As a result, evidence for the precipitation of nanoscale is discussed. The effect of crystallographic orientation is studied, where [001] aligned evaporation is found to develop compositional aberrations.

Effect of Doppler broadening on giant self-Kerr nonlinearity in a five-level ladder-type system

In this paper, we propose an analytical model to study the effect of Doppler broadening on self-Kerr nonlinearity in a five-level ladder-type atomic system. First- and third-order susceptibilities and the self-Kerr nonlinear coefficient are found as the function of temperature and parameters of laser fields. The analytical model is applied to hot $^{85}{\rm Rb}$85Rb and $^{87}{\rm Rb}$87Rb atoms, and it is shown that under the electromagnetically induced transparency (EIT) effect, the self-Kerr nonlinear coefficient is enhanced around three transparent spectral regions. When the temperature of atomic vapor increases (i.e., Doppler width increases), the depth and width of the EIT windows decrease accordingly, and therefore the amplitude of the Kerr nonlinear coefficient decreases significantly. In addition, because the frequency gaps between hyperfine levels of upper excited state ${{5\rm D}_{5/2}}$5D5/2 of $^{85}{\rm Rb}$85Rb atoms are much smaller than those of $^{87}{\rm Rb}$87Rb atoms, the EIT windows as well as the nonlinear dispersion curves for $^{85}{\rm Rb}$85Rb atoms are closer than those for $^{87}{\rm Rb}$87Rb atoms as the Doppler effect presents. The analytical results agree well with the experimental observation when reducing to a three-level atomic system. The analytical model can be used to easily fit the experimental observations of self-Kerr nonlinearity in a five-level atomic system under different temperature conditions and apply to a variety of applications relating to all-optical-switching techniques.

Microwave Rabi resonances beyond the small-signal regime

The coupling between microwave fields and atoms (or atom-like systems) is inherently weaker than for optical fields, making microwave signal manipulation for applications like quantum information processing technically challenging. In order to better understand this coupling and to develop tools for measuring it, we explore the microwave coupling to atoms using the "atomic candle" technique, and push it beyond the bounds of the small-signal regime in order to deliver a larger signal. In familiar two-level systems, responses beyond the usual Rabi oscillations can arise when a single-tone drive is phase-modulated, causing the steady-state populations to oscillate at integer harmonics of the modulation frequency. Resonant behavior of the first two harmonics for frequencies near the Rabi frequency, known as $\alpha$ and $\beta$ Rabi resonances, is widely used for microwave-field magnetometry and as a power standard known as the atomic candle. Here, we explore Rabi resonances beyond the small-signal approximation and report upon experimental observations of higher-harmonic population response for microwave hyperfine transitions in cold $^{87}\rm Rb$ atoms, which we compare to numerical simulations.

Generalized Hydrodynamics on an Atom Chip.

The emergence of a special type of fluidlike behavior at large scales in one-dimensional (1D) quantum integrable systems, theoretically predicted in O. A. Castro-Alvaredo etal., Emergent Hydrodynamics in Integrable Quantum Systems Out of Equilibrium, Phys. Rev. X 6, 041065 (2016)10.1103/PhysRevX.6.041065 and B. Bertini etal., Transport in Out-of-Equilibrium XXZ Chains: Exact Profiles of Charges and Currents, Phys. Rev. Lett. 117, 207201 (2016)10.1103/PhysRevLett.117.207201, is established experimentally, by monitoring the time evolution of the insitu density profile of a single 1D cloud of ^{87}Rb atoms trapped on an atom chip after a quench of the longitudinal trapping potential. The theory can be viewed as a dynamical extension of the thermodynamics of Yang and Yang, and applies to the whole range of repulsive interaction strength and temperature of the gas. The measurements, performed on weakly interacting atomic clouds that lie at the crossover between the quasicondensate and the ideal Bose gas regimes, are in very good agreement with the theory. This contrasts with the previously existing "conventional" hydrodynamic approach-that relies on the assumption of local thermal equilibrium-which is unable to reproduce the experimental data.

Thermal Global Expansion Coefficient Measurement for a Harmonic Trapped Gas Across Bose-Einstein Condensation

We report the measurement of the global thermal expansion coefficient of a confined Bose gas of $^{87}\rm Rb$ in a harmonic potential around the Bose-Einstein condensation transition temperature. We use the concept of global thermodynamic variables, previously introduced and appropriated for a non-homogeneous system. We observe the behavior of the thermal expansion coefficient above and below the critical temperature showing the lambda-like shape present in superfluid helium. The study demonstrates the potentiality of global thermodynamic variables for the investigation of properties across the critical temperature and a new way to study the thermodynamic properties of the quantum systems.

Probing structure, electronic property, and hydrogen adsorption for the alkali auride series

The structural evolution, relative stability, electronic property, and hydrogen adsorption of the alkali auride series, AunM (\( n = 1-8\)), \( {\rm M}= {\rm Li}\), Na, K, Rb, Cs), have been investigated using the density functional theory calculations at PW91 level. For the lowest-energy clusters, the dopant atom M prefers to occupy a peripheral or capped site in the host, and M-induced geometries become three-dimensional more easily. The average binding energy per atom, fragmentation energy, second-order difference of energy, and HOMO-LUMO energy gap show a pronounced odd-even oscillation with the number of Au atoms, and the enhanced relative stabilities are found in Au5M (\( {\rm M}= {\rm Li}\), Na, K) and Au3M (\( {\rm M}= {\rm Rb}\), Cs) clusters. In these clusters, the H2 molecule would like to bond with Au atom rather than impurity atom. After adsorption, the AunM structures and H2 molecule in all AunM-H2 clusters are hardly perturbed and still maintain their structural integrity. The geometrical and energetic information indicates a weak adsorption of H2 molecule.

Publisher's Note: Line shapes and time dynamics of the Förster resonances between two Rydberg atoms in a time-varying electric field [Phys. Rev. A 94 , 043417 (2016)

The observation of the Stark-tuned F\"orster resonances between Rydberg atoms excited by narrowband cw laser radiation requires usage of a Stark-switching technique in order to excite the atoms first in a fixed electric field and then to induce the interactions in a varied electric field, which is scanned across the F\"orster resonance. In our experiments with a few cold Rb Rydberg atoms we have found that the transients at the edges of the electric pulses strongly affect the line shapes of the F\"orster resonances, since the population transfer at the resonances occurs on a time scale of $\sim$100 ns, which is comparable with the duration of the transients. For example, a short-term ringing at a certain frequency causes additional radio-frequency-assisted F\"orster resonances, while non-sharp edges lead to asymmetry. The intentional application of the radio-frequency field induces transitions between collective states, whose line shape depends on the interaction strengths and time. Spatial averaging over the atom positions in a single interaction volume yields a cusped line shape of the F\"orster resonance. We present a detailed experimental and theoretical analysis of the line shape and time dynamics of the Stark-tuned F\"orster resonances ${\rm Rb}(nP_{3/2} )+{\rm Rb}(nP_{3/2} )\to {\rm Rb}(nS_{1/2} )+{\rm Rb}([n+1]S_{1/2} )$ for two Rb Rydberg atoms interacting in a time-varying electric field.

Gigahertz nanomechanical oscillators based on ions inside cyclic peptide nanotubes: a continuum study

The present work aims to investigate the mechanical oscillatory behavior of ions, and in particular \({{\rm Li}^{+}, {\rm Na}^{+}, {\rm Rb}^{+}}\) and \({{\rm Cl}^{-}}\) ions, inside a cyclo[(–d-Ala–l-Ala)4–] peptide nanotube using the continuum approximation along with the 6–12 Lennard–Jones (LJ) potential function. Assuming that each peptide unit is comprised of an inner and an outer tube, the van der Waals (vdW) potential energy and interaction force between an ion and a cyclic peptide nanotube (CPN) are determined analytically. With respect to the present formulations, a detailed parametric study is conducted on the vdW potential energy and interaction force distributions by varying the number of peptide units. Employing the conservation of mechanical energy principle, a novel expression for precise evaluation of oscillation frequency is introduced. To verify the accuracy of the proposed frequency expression, the results obtained from energy equation are compared with the ones predicted through solving the equation of motion numerically. The effects of number of peptide units and initial conditions including initial separation distance and velocity on the oscillatory behavior of various ions inside CPNs are explored. Among the considered ions, \({{\rm Cl}^{-}}\) ion is found to generate the highest frequency. According to the potential energy profile, one oscillatory zone for one peptide unit and different oscillatory zones for more than one peptide unit are observed. Numerical results indicate that optimal frequency decreases with increasing the number of peptide units and almost remains unchanged when the number of peptide units exceeds four.

Degenerate eigenvalues for Hamiltonians with no obvious symmetries

Certain Hamiltonians, based on two coupled quantum mechanical\break spins, exhibit degenerate eigenvalues despite having no obvious non-Abelian symmetries. Operators acting to permute the degenerate states do not have a simple form when expressed as polynomials of the generators of rotations for the respective spins. As observed in [3], one such Hamiltonian helps explain resonances in the spin relaxation rate of optically pumped ${\rm Rb}_2$, as a function of applied magnetic field. We give an explanation of why the degeneracies exist, based on properties of the commutator and anti-commutator of the Hamiltonian and its image under magnetic field reversal.

Thermodynamics of a trapped Bose-Fermi mixture

By using the Hartree-Fock-Bogoliubov equations within the Popov approximation, we investigate the thermodynamic properties of a dilute binary Bose-Fermi mixture confined in an isotropic harmonic trap. For mixtures with an attractive Bose-Fermi interaction we find a sizable enhancement of the condensate fraction and of the critical temperature of Bose-Einstein condensation with respect to the predictions for a pure interacting Bose gas. Conversely, the influence of the repulsive Bose-Fermi interaction is less pronounced. The possible relevance of our results in current experiments on trapped $^{87}{\rm Rb}-^{40}${\rm K} mixtures is discussed.

Metabolism of 83 Rb and 137 Cs in Persons with Muscle Disease

A double tracer of the muscle-seeking radionuclides ${}^{83}{\rm Rb}+{}^{137}{\rm Cs}$ was administered orally to persons of various ages, 16 with and 22 without muscle disease...