We investigate nuclear-resonant electron scattering as occurring in the two-step process of nuclear excitation by electron capture (NEEC) followed by internal conversion. The nuclear excitation and decay are treated by a phenomenological collective model in which nuclear states and transition probabilities are described by experimental parameters. We present capture rates and resonant strengths for a number of heavy ion collision systems considering various scenarios for the resonant electron scattering process. The results show that for certain cases resonant electron scattering can have significantly larger resonance strengths than NEEC followed by the radiative decay of the nucleus. We discuss the impact of our findings on the possible experimental observation of NEEC.
Photoionization of an atom in the presence of a neighboring atom of different species is studied. The latter first undergoes resonant photoexcitation, leading to an autoionizing state of the diatomic system. Afterwards, the excitation energy is transferred radiationlessly via a two-center Auger process to the other atom, causing its ionization. Assuming a fixed internuclear distance, it has been predicted theoretically that this indirect ionization pathway can strongly dominate over the direct photoionization. Here, we extend the theory of resonant two-center photoionization by including the n…
Electronic bridge excitation of the 76 eV nuclear isomeric state in $^{235}$U is shown to be strongly enhanced in the U$^{7+}$ ion, potentially enabling laser excitation of this nucleus. This is because the electronic spectrum has a very high level density near the nuclear transition energy that ensures the resonance condition is fulfilled. We present a quantum statistical theory based on many-body quantum chaos to demonstrate that typical values for the electronic factor increase the probability of electronic bridge in $^{235}$U$^{7+}$ by many orders of magnitude. We also extract the nuclear …
We propose a novel way to image dynamical properties of nonstationary electron systems using ultrafast resonant x-ray scattering. Employing a rigorous theoretical analysis within the framework of quantum electrodynamics, we demonstrate that a single scattering pattern from a nonstationary electron system encodes the instantaneous interatomic electron current in addition to the structural information usually obtained by resonant x-ray scattering from stationary systems. Thus, inelastic contributions that are indistinguishable from elastic processes induced by a broadband probe pulse, instead of…
The polarization properties of the elastic electron scattering on H-like ions are investigated within the framework of the relativistic QED theory. The polarization properties are determined by a combination of relativistic effects and spin exchange between the incident and bound electrons. The scattering of a polarized electron on an initially unpolarized ion is fully described by five parameters. We study these parameters for non-resonant scattering, as well as in the vicinity of LL resonances, where scattering occurs through the formation and subsequent decay of intermediate autoionizing st…
We review the ideas and concepts for a clock that is based on a radiative transition in the nucleus rather than in the electron shell. This type of clock offers advantages like an insensitivity against field-induced systematic frequency shifts and the opportunity to obtain high stability from interrogating many nuclei in the solid state. Experimental work concentrates on the low-energy (about 8 eV) isomeric transition in Th-229. We review the status of the experiments that aim at a direct optical observation of this transition and outline the plans for high-resolution laser spectroscopy experi…
Dielectronic recombination (DR) of few-electron ions has evolved into a sensitive spectroscopic tool for highly charged ions. This is due to technological advances in electron-beam preparation and ion-beam cooling techniques at heavy-ion storage rings. Recent experiments prove unambiguously that DR collision spectroscopy has become sensitive to 2nd order QED and to nuclear effects. This review discusses the most recent developments in high-resolution spectroscopy of low-energy DR resonances, experimental studies of KLL DR of very heavy hydrogenlike ions, isotope shift measurements of DR resona…
Nuclear resonant excitation of the 29.19-keV level in $^{229}$Th with high-brilliance synchrotron- radiation and detection of its decay signal, are proposed with the aim of populating the extremely low-energy isomeric state of $^{229}$Th.The proposed experiment, known as nuclear resonant scattering (NRS), has the merit of being free from uncertainties about the isomer level energy. However, it requires higher time resolution and shorter tail in the response function of the detector than that of conventional NRS experiments because of the short lifetime of the 29.19-keV state. We have fabricate…
We demonstrate how the technique of ultrafast resonant x-ray scattering can be applied to imaging dynamics of electronic wave packets in crystals. We study scattering patterns from crystals with electron dynamics in valence bands taking into account that inelastic and elastic scattering events induced by a broad-band probe pulse cannot be separated through the spectroscopy of the scattered photon. As a result, scattering patterns are not determined by the structure factor at the time of measurement, but can encode the instantaneous electron current between scattering atoms. We provide examples…
This paper theoretically treats the spontaneous resonant inelastic scattering of Laguerre-Gauss (LG) beams from the totally symmetric vibrations of complex polyatomic molecules within the semi-classical framework. We develop an interaction Hamiltonian that accounts for the position of the molecule within the excitation beam to derive the effective differential scattering cross-section of a classical LG beam from a molecule using the frequency domain third order nonlinear optical response function. To gain physical insight into this scattering process, we utilize a model vibronic molecule to st…
We consider Feshbach scattering of fermions in a one-dimensional optical lattice. By formulating the scattering theory in the crystal momentum basis, one can exploit the lattice symmetry and factorize the scattering problem in terms of center-of-mass and relative momentum in the reduced Brillouin zone scheme. Within a single band approximation, we can tune the position of a Feshbach resonance with the center-of-mass momentum due to the non-parabolic form of the energy band.
Interactions in a spin-polarized ultracold Fermi gas are governed by $p$-wave collisions and can be characterized by the $p$-wave scattering volume. Control of these collisions by Feshbach resonances is hampered by huge inelastic losses. Here, we suggest non-resonant light control of $p$-wave collisions, exploiting the anisotropic coupling of non-resonant light to the polarizability of the atoms. The $p$-wave scattering volume can be controlled by strong non-resonant light, in close analogy to the $s$-wave scattering length. For collision partners that are tightly trapped, the non-resonant lig…
A pair of atoms interacts with non-resonant light via its anisotropic polarizability. This effect can be used to tune the scattering properties of the atoms. Although the light-atom interaction varies with interatomic separation as $1/R^{3}$, the effective s-wave potential decreases more rapidly, as $1/R^{4}$ such that the field-dressed scattering length can be determined without any formal difficulty. The scattering dynamics are essentially governed by the long-range part of the interatomic interaction and can thus be accurately described by an asymptotic model [Crubellier et al., New J. Phys…
We observe and analyze d-wave resonant scattering of bosons in tightly confining harmonic waveguides. It is shown that the d-wave resonance emerges in the quasi-1D regime as an imprint of a 3D d-wave shape resonance. A scaling relation for the position of the d-wave resonance is provided. By changing the trap frequency, ultracold scattering can be continuously tuned from s-wave to d-wave resonant behavior. The effect can be utilized for the realization of ultracold atomic gases interacting via higher partial waves and opens a novel possibility for studying strongly correlated atomic systems be…
In the annihilation of a positron with a bound atomic electron, the virtual gamma photon created may excite the atomic nucleus. We put forward this effect as a spectroscopic tool for an energy-selective excitation of nuclear transitions. This scheme can efficiently populate nuclear levels of arbitrary multipolarities in the MeV regime, including monopole transitions and giant resonances. In certain cases, it may have a higher cross sections than the conventionally used Coulomb excitation.
Future ultrafast x-ray light sources might image ultrafast coherent electron motion in real-space and in real-time. For a rigorous understanding of such an imaging experiment, we extend the theory of non-resonant x-ray scattering to the time-domain. The role of energy resolution of the scattering detector is investigated in detail. We show that time-resolved non-resonant x-ray scattering with no energy resolution offers an opportunity to study time-dependent electronic correlations in non- equilibrium quantum systems. Furthermore, our theory presents a unified description of ultrafast x-ray sc…
We formulate the Born approximation for finding resonance poles in the complex plane for potential scattering problems. Using the method, we study the distribution of resonance poles for several scattering potentials. In particular, we find for an exponential potential with a cutoff that the cutoff generates an infinite series of extra resonance poles below and along the real axis, which would not exist without the cutoff. We also find for a Gaussian potential that the series of resonance poles approach the imaginary axis of the complex energy plane from left. In other words, the real parts of…
