arXiv subjects

Adriana Pálffy

Publications and source records attributed to Adriana Pálffy.

At least 19 recordsLinked to original sources

arXiv2026

Sensitivity of the $^{229m}$Th clock transition to the fine-structure constant in a Skyrme-Hartree-Fock-BCS approach

The sensitivity of the $^{229m}$Th isomer transition frequency to the possible temporal variation of the fine-structure constant $α$ is investigated theoretically. We evaluate both the Coulomb as well as the isomer energies in a selfconsistent Hartree-Fock plus Bardeen-Cooper-Schrieffer (BCS) approach with Skyrme energy density functional, taking a detailed account of the nuclear shape deformation and pairing correlations. Our results show that by a fine tuning of the pairing strengths and considering axial octupole deformation, the model can predict a very low isomer energy below the keV limit, which is not accessible in the presence of imposed reflection symmetry. Furthermore, in the model solution with octupole deformation, the difference between the Coulomb energy in the isomeric and ground states is one order of magnitude larger than for the case with imposed reflection symmetry. These results allow for a fully theoretical prediction of the sensitivity of the isomer transition frequency to $α$ in the framework of a microscopic nuclear model, yielding values of $K\sim 10^3-10^4$, and for a deeper understanding of its underlying physical conditions.

nucl-th↗

arXiv2026

Bulk spectra and the non-Hermitian skin effect in systems with long-range couplings

To achieve translational symmetry for the computation of the band structure of a lattice model, one can either consider an infinite lattice or impose periodic boundary conditions (PBC). While in systems with short-range couplings these two approaches are equivalent, we show that for long-range couplings one can obtain considerably different results. We compare the two methods on the basis of one-dimensional quantum emitter chains both in free space and when coupled to a waveguide. The latter system allows for asymmetric couplings enabling the non-Hermitian skin effect, which we analyze using the two different band-structure calculation methods. We find that only PBC lead to physically and mathematically robust results, while the infinite-chain approach entails convergence issues and is unable to satisfyingly explain the emergence of the non-Hermitian skin effect in the waveguide system. Using PBC reveals unusual findings like a non-star shaped generalized Brillouin zone and strongly localized eigenstates with zero winding number.

quant-ph↗

arXiv2026

Nuclear non-resonant photoexcitation assisted by electron recombination

We investigate theoretically a nuclear excitation mechanism involving absorption of non-resonant photons leveraged by the coupling to the atomic shell. The nuclear non-resonant photoexcitation is assisted by electron recombination which compensates the energy mismatch between photon and nuclear transition energies, reminiscent of parametric up-conversion in non-linear media. This third-order process proceeds via a virtual nuclear state rather than virtual electronic states, distinguishing this mechanism from the electronic bridge. We investigate the process on the example of a so-far not observed 14.2 keV hard x-ray transition in 193Pt driven by an x-ray free-electron laser. Although the calculated cross section is small, it can be compensated by the vast number of non-resonant photons from the x-ray laser pulse. By enabling nuclear excitation through non-resonant photons, this up-conversion-like mechanism suggests new directions for non-linear x-ray interactions mediated by nuclear transitions.

nucl-th↗

arXiv2026

Phase-enhanced excitations in pumped collective nuclear systems

The quantum dynamics of an externally driven ensemble of nuclear two-level systems embedded in a leaky broadband cavity is investigated theoretically. In the considered scenario both the nuclear ensemble and the cavity mode are coherently pumped by two externally applied x-ray electromagnetic fields. When the frequencies of the applied coherent fields are identical, cross-correlations among the existing decay channels increase the nuclear excitation probabilities depending on the phase difference of the applied fields. Our results show that the excited state of the nuclear ensemble may exhibit sub- to super-Poissonian nuclear statistics, demonstrating induced correlations during photon absorption or emission processes. The role of cross-correlations for the superradiant decay and the collective Lamb shift of the ensemble is also investigated.

quant-ph↗

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

Polarization-dependent topology in quantum emitter chains

The role of polarization in the topology of quantum emitter chains is investigated theoretically, whereby "polarization" refers to the transition dipole moments of the emitters. We show that, if the chain is zigzag-shaped, different topological phases can be realized by adjusting the polarization direction. It turns out that long-range dipole-dipole couplings weaken the bulk-boundary correspondence, but on the other hand give rise to higher-order topological phases with four observable edge modes. We also demonstrate how the polarization orientation can be used to define an additional dimension and simulate a synthetic Chern insulator. Our findings open up a way to actively switch between various topological phases within a single arrangement of quantum emitters.

quant-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↗

arXiv2025

Collective nuclear excitation and pulse propagation in single-mode x-ray waveguides

Waveguides offer a means to controllably couple atomic ensembles to the electromagnetic field therein. Here, we demonstrate x-ray propagation in planar thin-film waveguides coupled to Mössbauer nuclei under collective resonant excitation by short pulses of synchrotron radiation. We record x-ray photons that have been emitted into resonant modes of the waveguide. Depending on the geometry and mode of excitation, two fundamentally different signatures of the collective emission are observed, for which we present a unifying theoretical model. Our results form a new platform for waveguide quantum electrodynamics in the hard x-ray regime with the potential to provide a coherent narrowband source of x-rays on the nanometer scale.

quant-ph↗

arXiv2025

Probing Nuclear Excitation by Electron Capture in an Electron Beam Ion Trap with Non-destructive Isomer Detection via Precision Mass Spectrometry

Nuclear excitation by electron capture (NEEC) is an important nuclear excitation mechanism which still lacks conclusive experimental verification. This is primarily attributed to strong background x-/$γ$-ray noise and competing nuclear excitation processes which would overshadow the signals in various environments that NEEC takes place. Here, we propose an experimental approach to observe the NEEC process within a background-free environment. Through collisions with a highly-compressed mono-energetic electron beam in an electron beam ion trap, nuclei may get excited to a long-lived isomeric state via the NEEC process. Subsequently, ions can be extracted and Penning-trap mass spectrometry employed to unambiguously detect the isomer. Our study focuses on the promising candidate $^{189}\mathrm{Os}$, demonstrating measurable detection rates of the NEEC process and discussing the feasibility of the proposed approach. This new approach for observing the NEEC process may be realized in the near future.

nucl-ex↗

arXiv2024

Skyrme-Hartree-Fock-BCS approach to $^{229m}$Th and neighboring nuclei

The microscopic origin of the $^{229m}$Th isomer and its possible manifestation also in neighboring nuclei is explored within a selfconsistent Skyrme Hartree-Fock plus Bardeen-Cooper-Schrieffer approach. By using the well established SIII Skyrme parametrization, without any special adjustments related to low-energy isomer, the single-particle spectrum provided by the model reproduces the correct isomer $K^π=3/2^{+}$ spin and parity, and the relative proximity of the isomeric state to the $K^π=5/2^{+}$ ground state, yet on the keV scale. We show that this approach may provide microscopic estimates for some related observables, such as the quadrupole and octupole moments, deformation parameters as well as magnetic dipole moments. Its ability to provide a prediction for the M1 isomer transition probability is discussed. The obtained $^{229}$Th single-particle structure is compared with that provided by calculations in neighbouring actinide isotopes and isotones, allowing us to assess the more general role of the considered mechanism for the formation of low-energy isomers.

nucl-th↗

arXiv2024

Efficient production of $^{229m}$Th via nuclear excitation by electron capture

The nuclear isomeric state $^{229m}$Th with an exceptionally low excitation energy makes the $^{229}$Th isotope a crucial candidate for nuclear clocks and many other applications. Efficient and controllable production of $^{229m}$Th is essential and still remains a challenge. Here we report a novel approach for efficient production of $^{229m}$Th by the excitation of $^{229}$Th to the above-lying excited state at $29.19$ keV energy via the process of nuclear excitation by electron capture (NEEC). We show theoretically that the production rate of $^{229m}$Th per nucleus with accessible conditions can be six orders of magnitude larger than the value experimentally demonstrated using $29$-keV synchrotron radiation for this indirect excitation. With the efficient production of $^{229m}$Th, our results identify scenarios, as well as the characteristic NEEC signature with which NEEC events could be unambiguously identified, for a clear experimental identification of the long-sought NEEC phenomenon.

nucl-th↗

arXiv2024

Neural-network-supported basis optimizer for the configuration interaction problem in quantum many-body clusters: Feasibility study and numerical proof

A deep-learning approach to optimize the selection of Slater determinants in configuration interaction calculations for condensed-matter quantum many-body systems is developed. We exemplify our algorithm on the discrete version of the single-impurity Anderson model with up to 299 bath sites. Employing a neural network classifier and active learning, our algorithm enhances computational efficiency by iteratively identifying the most relevant Slater determinants for the ground-state wavefunction. We benchmark our results against established methods and investigate the efficiency of our approach as compared to other basis truncation schemes. Our algorithm demonstrates a substantial improvement in the efficiency of determinant selection, yielding a more compact and computationally manageable basis without compromising accuracy. Given the straightforward application of our neural network-supported selection scheme to other model Hamiltonians of quantum many-body clusters, our algorithm can significantly advance selective configuration interaction calculations in the context of correlated condensed matter.

cond-mat.str-el↗

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↗

arXiv2023

Deep-learning approach for the atomic configuration interaction problem on large basis sets

High-precision atomic structure calculations require accurate modelling of electronic correlations typically addressed via the configuration interaction (CI) problem on a multiconfiguration wave function expansion. The latter can easily become challenging or infeasibly large even for advanced supercomputers. Here we develop a deep-learning approach which allows to preselect the most relevant configurations out of large CI basis sets until the targeted energy precision is achieved. The large CI computation is thereby replaced by a series of smaller ones performed on an iteratively expanding basis subset managed by a neural network. While dense architectures as used in quantum chemistry fail, we show that a convolutional neural network naturally accounts for the physical structure of the basis set and allows for robust and accurate CI calculations. The method was benchmarked on basis sets of moderate size allowing for the direct CI calculation, and further demonstrated on prohibitively large sets where the direct computation is not possible.

physics.atom-ph↗

arXiv2022

Quantum effects on plasma screening for thermonuclear reactions in laser-generated plasmas

A quantum plasma screening model based on the density matrix formalism is used to investigate theoretically the thermonuclear reactions $^{13}$C($α$, $n$)$^{16}$O and $^2$H($d$, $n$)$^3$He in laser-generated plasmas over a large range of densities and temperatures. For cold and dense (solid-state density) plasmas, our results show that quantum effects can enhance the plasma screening for thermonuclear reactions up to one order of magnitude compared to the classical case. This result can have impact on nuclear astrophysics predictions, and also may play a role for fusion energy gain prospects. Our simulations allow us to identify the laser-generated plasma experimental setting in which the quantum effects on plasma screening could be confirmed at existing high-intensity laser facilities.

physics.plasm-ph↗

arXiv2022

Nuclear phase retrieval spectroscopy using resonant x-ray scattering

Light-matter interaction is exploited in spectroscopic techniques to access information about molecular, atomic or nuclear constituents of the sample of interest. While scattered light carries both amplitude and phase information of the electromagnetic field, most of the time the latter is lost in intensity measurements. However, often the phase information is paramount to reconstruct the desired information of the target, as it is well known from coherent x-ray imaging. Here we introduce a new phase retrieval algorithm which allows us to reconstruct the field phase information from two-dimensional time- and energy-resolved spectra. We apply this method to the particular case of x-ray scattering off Mössbauer nuclei at a synchrotron radiation source. Knowledge of the phase allows also for an excellent reconstruction of the energy spectra from experimental data, which could not be achieved with this resolution otherwise. Our approach provides an efficient novel data analysis tool which will benefit x-ray quantum optics and Mössbauer spectroscopy with synchrotron radiation alike.

physics.ins-det↗