arXiv subjects

Tobias Kirschbaum

Publications and source records attributed to Tobias Kirschbaum.

6 recordsLinked to original sources

arXiv2026

Nuclear forward scattering of Bessel beams in $^{229}$Th:CaF$_2$

The coherent pulse propagation of a Bessel beam resonant to the 8.4 eV nuclear clock transition in $^{229}$Th-doped crystals is investigated theoretically. Due to the magnetic dipole character of the clock transition, Bessel beams which present non-uniform transverse profiles and carry orbital angular momentum might enhance excitation channels or offer new control degrees of freedom compared to standard plane waves. We model the nuclear forward scattering of a resonant Bessel beam pulse propagating through the crystal, extending an formalism based on the iterative wave equation for plane waves. Thereby we take into account the nuclear quadrupole splitting in the crystal, considering the possibility of multiple quantization axes and present results for scenarios involving a single nuclear transition and multiple simultaneously driven transitions, analyzing temporal and spatial intensity patterns. Our findings show that the propagation of Bessel beams can be used to determine the relative distribution of different directions of quantization axes inside the crystal.

physics.atom-ph↗

arXiv2025

Density Functional Theory Study of Th-doped LiCAF and LiSAF for Nuclear Clock Applications

Thorium-doped LiCaAlF$_6$ and LiSrAlF$_6$ (Th:LiCAF and Th:LiSAF) are promising crystals for a solid-state nuclear clock based on the 8 eV transition in $^{229}$Th; however, their complex crystal structures complicate understanding the atomic arrangement of the thorium defects. In this work, density functional theory simulations are employed to systematically investigate these systems, including temperature-dependent effects and environmental conditions of fluorine saturation and deficiency. We investigated 20 distinct charge compensation schemes for each material, revealing lower defect formation energies in Th:LiSAF than in Th:LiCAF. This suggests that the former may attain a higher concentration of thorium nuclei. Furthermore, we calculated the electric field gradient for the lowest energy structure per compensation pathway. Our investigation shows that results previously reported in the literature apply only to a subset of experimental conditions.

cond-mat.mtrl-sci↗

arXiv2025

Electronic Bridge processes in $^{229}$Th-doped LiCAF and LiSAF

Electronic bridge mechanisms driving the $^{229}$Th nuclear clock transition in the vacuum-ultraviolet-transparent crystals $^{229}$Th:LiCAF (LiCaAlF$_6$) and $^{229}$Th:LiSAF (LiSrAlF$_6$) are investigated theoretically. Due to doping-induced symmetry breaking within the host crystal, electronic defect states emerge around the thorium nucleus and can facilitate nuclear (de)excitation via laser-assisted electronic bridge mechanisms. We investigate spontaneous and laser-assisted electronic bridge schemes for different charge compensation mechanisms. While the calculated spontaneous electronic bridge rates are very small, laser-assisted electronic bridge schemes for nuclear (de)excitation turn out to be significantly more efficient than both spontaneous nuclear decay and direct laser excitation, offering promising prospects for the future clock operation.

physics.atom-ph↗

arXiv2024

Photoexcitation of the $^{229}$Th nuclear clock transition using twisted light

The $^{229}$Th nucleus has a unique transition at only 8 eV which could be used for a novel nuclear clock. We investigate theoretically the prospects of driving this transition with vortex light beams carrying orbital angular momentum. Numerical results are presented for two experimental configurations which are promising for the design of the planned nuclear clock: a trapped ion setup and a large ensemble of nuclei doped into CaF$_2$ crystals which are transparent in the frequency range of the nuclear transition. We discuss the feasibility of the vortex beam nuclear excitation and compare the excitation features with the case of plane wave beams.

physics.atom-ph↗

arXiv2023

Excitation and probing of low-energy nuclear states at high-energy storage rings

$^{229}$Th with a low-lying nuclear isomeric state is an essential candidate for a nuclear clock as well as many other applications. Laser excitation of the isomeric state has been a long-standing goal. With relativistic $^{229}$Th ions in storage rings, high-power lasers with wavelengths in the visible range or longer can be used to achieve high excitation rates of $^{229}$Th isomers. This can be realized through direct resonant excitation, or excitation via an intermediate nuclear or electronic state, facilitated by the tunability of both the laser-beam and ion-bunch parameters. Unique opportunities are offered by highly charged $^{229}$Th ions due to the nuclear-state mixing. The significantly reduced isomeric-state lifetime corresponds to a much higher excitation rate for direct resonant excitation. Importantly, we propose electric dipole transitions changing both the electronic and nuclear states that are opened by the nuclear hyperfine mixing. We suggest using them for efficient isomer excitation in Li-like $^{229}$Th ions, via stimulated Raman adiabatic passage or single-laser excitation. We also propose schemes for probing the isomers, utilizing nuclear radiative decay or laser spectroscopy on electronic transitions, through which the isomeric-state energy can be determined with an orders-of-magnitude higher precision than the current value. The schemes proposed here for $^{229}$Th could also be adapted to low-energy nuclear states in other nuclei, such as $^{229}$Pa.

nucl-ex↗

arXiv2022

Nuclear coherent population transfer to the $^{229m}$Th isomer using x-ray pulses

Population of the 8 eV $^{229m}$Th isomer via the second nuclear excited state at 29.19 keV by means of coherent x-ray pulses is investigated theoretically. We focus on two nuclear coherent population transfer schemes using partially overlapping x-ray pulses known from quantum optics: stimulated Raman adiabatic passage (STIRAP), and successive $π$ pulses. Numerical results are presented for three possible experimental setups. Our results identify the Gamma Factory as the most promising scenario, where two ultraviolet pulses combined with relativistically accelerated ions deliver the required intensities for efficient isomer population. Our simulations require knowledge of the in-band and cross-band nuclear transition probabilities. We give theoretically predicted values for the latter and discuss them in the context of recent experiments.

nucl-th↗