Atomic Physics Latest Preprints | 2019-07-03
Atomic Physics
Multi-Frequency Atom-Photon Interactions (1907.01469v1)
Ben Yuen, Christopher J. Foot
2019-07-02
We present a formalism that enables the analytic calculation of the interaction of a spin-half particle with a polychromatic electromagnetic field. This powerful new approach provides a clear physical picture even for cases with highly degenerate energy levels, which are complicated to interpret in the standard dressed-atom picture. Typically semi-classical methods are used for such problems (leading to equations that are solved by Floquet theory). Our formalism is derived from quantum electrodynamics and thus is more widely applicable. In particular it makes accessible the intermediate regime between quantum and semi-classical dynamics. We give examples of the application to multi-frequency multi-photon processes in strong fields by deriving the Hamiltonians of such systems, and also to the dynamics of weak fields at long times for which semi-classical methods are insufficient.
Gravitational effects on geonium and free electron 
-factor measurements in a Penning trap (1907.01460v1)
Sebastian Ulbricht, Robert Alexander Müller, Andrey Surzhykov
2019-07-02
We present a theoretical analysis of an electron confined by a Penning trap, also known as geonium, that is affected by gravity. In particular, we investigate the gravitational influence on the electron dynamics and the electromagnetic field of the trap. We consider the special case of a homogeneous gravitational field, which is represented by Rindler spacetime. In this spacetime the Hamiltonian of an electron with anomalous magnetic moment is constructed. Based on this Hamiltonian and the exact solution to Maxwell equations for the field of a Penning trap in Rindler spacetime, we derived the transition energies of geonium up to the relativistic corrections of
. These transition energies are used to obtain an extension of the well known
Observation of Interactions between Trapped Ions and Ultracold Rydberg Atoms (1809.03987v3)
N. V. Ewald, T. Feldker, H. Hirzler, H. Fürst, R. Gerritsma
2018-09-11
We report on the observation of interactions between ultracold Rydberg atoms and ions in a Paul trap. The rate of observed inelastic collisions, which manifest themselves as charge transfer between the Rydberg atoms and ions, exceeds that of Langevin collisions for ground state atoms by about three orders of magnitude. This indicates a huge increase in interaction strength. We study the effect of the vacant Paul trap's electric fields on the Rydberg excitation spectra. To quantitatively describe the exhibited shape of the ion loss spectra, we need to include the ion-induced Stark shift on the Rydberg atoms. Furthermore, we demonstrate Rydberg excitation on a dipole-forbidden transition with the aid of the electric field of a single trapped ion. Our results confirm that interactions between ultracold atoms and trapped ions can be controlled by laser coupling to Rydberg states. Adding dynamic Rydberg dressing may allow for the creation of spin-spin interactions between atoms and ions, and the elimination of collisional heating due to ionic micromotion in atom-ion mixtures.
Search for the correction term to the Fermi's golden rule in positron annihilation (1907.01264v1)
R. Ushioda, O. Jinnouchi, K. Ishikawa, T. Sloan
2019-07-02
In the positron-electron annihilation process, finite deviations from the standard calculation based on the Fermi's Golden rule are suggested in recent theoretical work. This paper describes an experimental test of the predictions of this theoretical work by searching for events with two photons from positron annihilation of energy larger than the electron rest mass (
). The positrons came from a
source, tagging the third photon from the spontaneous emission of
de-exitation to suppress backgrounds.
Measurements of individual and ensemble lifetimes of high-lying Rb Rydberg states (1907.01254v1)
M. Archimi, C. Simonelli, L. Di Virgilio, A. Greco, M. Ceccanti, E. Arimondo, D. Ciampini, I. I. Ryabtsev, I. I. Beterov, O. Morsch
2019-07-02
We demonstrate a hybrid method based on field ionization and state-selective de-excitation capable of measuring the lifetimes of high-lying Rydberg states. For nS Rydberg states of Rb atoms with principal quantum number
, we measure both the individual target state lifetimes and those of the ensemble of Rydberg states populated via black-body radiation-induced transitions. We find good overall agreement with numerical calculations of the expected lifetimes in both cases. However, for the target state lifetimes, we find a local deviation towards shorter lifetimes for states around
, which we interpret as a signature of a modified black-body spectrum in the finite volume in which our experiments take place.
Electric Rydberg-atom interferometery (1907.01234v1)
J. E. Palmer, S. D. Hogan
2019-07-02
An electric analogue of the longitudinal Stern-Gerlach matter-wave interferometer has been realized for atoms in Rydberg states with high principal quantum number,
. The experiments were performed with He atoms prepared in coherent superpositions of the
and
circular Rydberg states in zero electric field by a
pulse of resonant microwave radiation. These atoms were subjected to a pulsed inhomogeneous electric field to generate a superposition of momentum states before a
pulse was applied to invert the internal states. The same pulsed inhomogeneous electric field was then reapplied for a second time to transform the motional states to have equal momenta before a further
Semiclassical two-step model with quantum input: Quantum-classical approach to strong-field ionization (1907.01231v1)
N. I. Shvetsov-Shilovski, M. Lein
2019-07-02
We present a mixed quantum-classical approach to strong-field ionization - a semiclassical two-step model with quantum input. In this model the initial conditions for classical trajectories that simulate electron wave packet after ionization are determined by the exact quantum dynamics. As a result, the model allows to overcome deficiencies of standard semiclassical approaches in describing the ionization step. The comparison with the exact numerical solution of the time-dependent Schr"{o}dinger equation shows that for ionization of a one-dimensional atom the model yields quantitative agreement with the quantum result. This applies both to the width of the photoelectron momentum distribution and the interference structure.
Effect of electron correlations on attosecond photoionization delays in the vicinity of the Cooper minima of argon (1907.01219v1)
D. Hammerland, P. Zhang, A. Bray, C. F. Perry, S. Kuehn, P. Jojart, I. Seres, V. Zuba, Z. Varallyay, K. Osvay, A. Kheifets, T. T. Luu, H. J. Woerner
2019-07-02
Attosecond photoionization delays have mostly been interpreted within the single-particle approximation of multi-electron systems. The strong electron correlation between the photoionization channels associated with the 3p and 3s orbitals of argon presents an interesting arena where this single-particle approximation breaks down. Around photon energies of 42~eV, the 3s photoionization channel of argon experiences a
Cooper-like" minimum, which is exclusively the result of inter-electronic correlations with the 3p shell. Photoionization delays around thisCooper-like" minimum have been predicted theoretically, but experimental verification has remained a challenge since the associated photoionization cross section is inherently very low. Here, we report the measurement of photoionization delays around the Cooper-like minimum that were acquired with the 100~kHz High-Repetition 1 laser system at the ELI-ALPS facility. We report relative photoionization delays reaching up to unprecedented values of 430 +/- 20~as, as a result of electron correlation. Our experimental results are in partial agreement with state-of-the-art theoretical results, but also demonstrate the need for additional theoretical developments.
Ion survival in grazing collisions of H
with vicinal nanosurfaces probes subband electronic structures (1907.01074v1)
John Shaw, David Monismith, Yixao Zhang, Yixao Zhang, Himadri S. Chakraborty
2019-07-01
We study the electron dynamics at a monocrystalline Pd(111) surface with stepped vicinal nanostructures modeled in a simple Kronig-Penney scheme. The unoccupied bands of the surface are resonantly excited \textit{via} the resonant charge transfer (RCT) interaction of the surface with a hydrogen anion reflected at grazing angles. The interaction dynamics is simulated numerically in a quantum mechanical wave packet propagation approach. Visualization of the wave packet density shows that, when the electron is transferred to the metal, the surface and image subband states are the most likely locations of the electron as it evolves through the superlattice. The survival probability of the interacting ion exhibits strong modulations as a function of the vicinal-terrace size and shows peaks at those energies that access the image state subband dispersions. A simple square well model producing standing waves between the steps on the surface suggests the application of such ion-scattering at shallow angles to map electronic substructures in vicinal surfaces. The work also serves as the first proof-of-principle in the utility of our computational method to address, via RCT, surfaces with nanometric patterns.
Influence of atomic motion on the collective effects in dense and cold atomic ensembles (1907.01029v1)
A. S. Kuraptsev, I. M. Sokolov
2019-07-01
We show that atomic motion leads not only to noticeable quantitative, but in some cases also to qualitative modification of collective effects in dense and cold atomic ensembles even in the case when the characteristic Doppler shifts are tens of times smaller than the natural linewidth. The observed influence is explained as a result of the suppression of the impact of sub-radiant collective states caused by the displacement of the atoms.
