arXiv subjects

A. Borschevsky

Publications and source records attributed to A. Borschevsky.

At least 19 recordsLinked to original sources

arXiv2026

Ab Initio Calculations of the Static and Dynamic Polarizability of BaOH

We present high-precision ab initio calculations of the static and dynamic polarizability of the barium monohydroxide ($^{138}$BaOH) molecule, using relativistic coupled-cluster theory. By thoroughly investigating the dependence of the calculated polarizabilities on computational parameters (basis set size, treatment of relativity, level of treatment of electron correlation, and vibrational corrections), a procedure to determine uncertainties is constructed and applied. The dipole moment of BaOH is also calculated and compared to experiment, confirming the accuracy of the predicted polarizabilities. The static and dynamic ($λ=1064\;\text{nm}$) polarizability was calculated for both the ground state and the (010) vibrational bending mode, the latter state being particularly interesting for a wide range of quantum experiments. The ground state static polarizabilities were calculated to be 200.8(24) a.u. and 297(5) a.u. for the parallel and perpendicular components respectively.

physics.chem-ph↗

arXiv2026

Statistics and systematics of electron EDM searches with BaF

The NL-$e$EDM experiment searches for a non-zero electric dipole moment of the electron $d_e$ ($e$EDM) in the ground state of barium monofluoride (BaF). A beam of BaF from a supersonic expansion source is probed with the spin precession method presented in \cite{Boeschoten2024}. This method permits the extraction of an $e$EDM value as well as values for parameters causing a possible systematic bias leading to a false $e$EDM. The currently achievable sensitivity is limited by statistics collected in a period of 34 hours and yields an $d_e$ of $2(3) \times 10^{-25}$ $e\,$cm. Furthermore, from the same dataset sufficiently strong limits on parameters which can induce a false $e$EDM are extracted. These are mainly the electric field \textbf{E} and the intensity of the lasers fields in the fiducial volume of the experiment. We summarize the steps required to upgrade of the experiment to reach a competitive level on $d_e$, e.g. an intense laser-cooled beam from a cryogenic buffer gas source and the light collection efficiency of fluorescence.

physics.atom-ph↗

arXiv2025

Precision spectroscopy of the $A^2Π$ $\leftarrow$ $X^2Σ^+$ transition in BaF

High-resolution spectroscopy on the $A^2Π$ - $X^2Σ^+$ electronic system of $^{138}$Ba$^{19}$F is performed using a cold molecular beam produced by a buffer gas source. The hyperfine structure in both $X^2Σ^+$ ground and $A^2Π$ excited states is fully resolved and absolute transition frequencies of individual components are measured at the sub-MHz level making use of frequency-comb laser calibration. Sets of molecular constants for the $X^2Σ^+$($v=0,1$) and $A^2Π$($v=0,1$) levels are determined, with improved accuracy for the $T_{v',v''}$ band origins and spin-orbit interaction constants for the $A^2Π$ excited states, that represent the presently measured highly accurate transitions for low-$J$ states as well as previously determined transition frequencies in Fourier-transform emission studies for rotational levels as high as $J \geq 100$. The extracted molecular constants reproduce the measured transition frequencies at the experimental absolute accuracy of 1 MHz. The work is of relevance for future laser cooling schemes, and is performed in the context of a measurement of the electron dipole moment for which BaF is a target system.

physics.atom-ph↗

arXiv2025

Relativistic atomic structure calculations in support of spectroscopy

Theory can provide important support at all the stages of spectroscopic experiments, from planning the measurements to the interpretation of the results. Such support is particularly valuable for the challenging experiments on heavy, unstable, and superheavy elements and for precision measurements aimed at testing the Standard Model of particle physics. To be reliable and useful in experimental context, theoretical predictions should be based on high-accuracy calculations. For heavy elements, such calculations must treat both relativistic effects and electron correlation on the highest possible level. Relativistic coupled cluster is considered one of the most powerful methods for accurate calculations on heavy many-electron atoms and molecules. This approach is highly accurate and versatile and can be used to obtain energies and a variety of atomic and molecular properties. Furthermore, its robust and transparent formulation allows for systematic improvement of the accuracy of the calculated results and for assigning uncertainties on theoretical values. The Fock-space coupled cluster (FSCC) variant of this method is particularly useful in the context of spectroscopic measurements as it provides access to atomic spectra and properties of the excited states. In this review, we present in detail the relativistic coupled cluster approach and its FSCC variant. We provide a description of the computational procedure used for accurate calculations and for assigning uncertainties. Outstanding recent examples of application to atomic properties, focusing on the experimental context are presented. Finally, we provide a brief discussion of the perspectives for future developments and applications of the CC approach.

physics.atom-ph↗

arXiv2025

Laser spectroscopy and CP-violation sensitivity of actinium monofluoride

The apparent invariance of the strong nuclear force under combined charge conjugation and parity (CP) remains an open question in modern physics. Precision experiments with heavy atoms and molecules can provide stringent constraints on CP violation via searches for effects due to permanent electric dipole moments and other CP-odd properties in leptons, hadrons, and nuclei. Radioactive molecules have been proposed as highly sensitive probes for such searches, but experiments with most such molecules have so far been beyond technical reach. Here we report the first production and spectroscopic study of a gas-phase actinium molecule, $^{227}$AcF. We observe the predicted strongest electronic transition from the ground state, which is necessary for efficient readout in searches of symmetry-violating interactions. Furthermore, we perform electronic- and nuclear-structure calculations for $^{227}$AcF to determine its sensitivity to various CP-violating parameters, and find that a realistic, near-term experiment with a precision of 1 mHz would improve current constraints on the CP-violating parameter hyperspace by three orders of magnitude. Our results thus highlight the potential of $^{227}$AcF for exceptionally sensitive searches of CP violation.

physics.atom-ph↗

arXiv2025

Charge radii of neutron-rich scandium isotopes and the seniority symmetry in the $0f_{7/2}$ shell

Nuclear charge radii of neutron-rich $^{47-49}$Sc isotopes were measured using collinear laser spectroscopy at CERN-ISOLDE. The new data reveal that the charge radii of scandium isotopes exhibit a distinct trend between $N=20$ and $N=28$, with $^{41}$Sc and $^{49}$Sc isotopes having similar values, mirroring the closeness of the charge radii of $^{40}$Ca and $^{48}$Ca. Theoretical models that successfully interpret the radii of calcium isotopes could not account for the observed behavior in scandium radii, in particular the reduced odd-even staggering. Remarkably, the inclusion of the new $^{49}$Sc radius data has unveiled a similar trend in the charge radii of $N=28$ isotones and $Z=20$ isotopes when adding the neutrons atop the $^{40}$Ca core and the protons atop the $^{48}$Ca core, respectively. We demonstrate that this trend is consistent with the prediction of the seniority model.

nucl-ex↗

arXiv2024

Pinning down electron correlations in RaF via spectroscopy of excited states and high-accuracy relativistic quantum chemistry

We report the spectroscopy of the 14 lowest excited electronic states in the radioactive molecule radium monofluoride (RaF). The observed excitation energies are compared with fully relativistic state-of-the-art Fock-space coupled cluster (FS-RCC) calculations, which achieve an agreement of >=99.64% (within ~12 meV) with experiment for all states. Guided by theory, a firm assignment of the angular momentum and term symbol is made for 10 states and a tentative assignment for 4 states. The role of high-order electron correlation and quantum electrodynamics effects in the excitation energy of excited states is studied, found to be important for all states. Establishing the simultaneous accuracy and precision of calculations is an important step for research at the intersection of particle, nuclear, and chemical physics, including searches of physics beyond the Standard Model, for which RaF is a promising probe.

physics.atom-ph↗

arXiv2024

Ionization potential of radium monofluoride

The ionization potential (IP) of radium monofluoride (RaF) was measured to be 4.969(2)[10] eV, revealing a relativistic enhancement in the series of alkaline earth monofluorides. The results are in agreement with a relativistic coupled-cluster prediction of 4.969[7] eV, incorporating up to quantum electrodynamics corrections. Using the same computational methodology, an improved calculation for the dissociation energy ($D_{0}$) of 5.54[5] eV is presented. This confirms that radium monofluoride joins the small group of diatomic molecules for which $D_{0}>\mathrm{IP}$, paving the way for precision control and interrogation of its Rydberg states.

physics.atom-ph↗

arXiv2024

Radiative lifetime of the A 2Π1/2 state in RaF with relevance to laser cooling

The radiative lifetime of the $A$ $^2 Π_{1/2}$ (v=0) state in radium monofluoride (RaF) is measured to be 35(1) ns. The lifetime of this state and the related decay rate $Γ= 2.86(8) \times 10^7$ $s^{-1}$ are of relevance to the laser cooling of RaF via the optically closed $A$ $^2 Π_{1/2} \leftarrow X$ $^2Σ_{1/2}$ transition, which makes the molecule a promising probe to search for new physics. RaF is found to have a comparable photon-scattering rate to homoelectronic laser-coolable molecules. Thanks to its highly diagonal Franck-Condon matrix, it is expected to scatter an order of magnitude more photons than other molecules when using just 3 cooling lasers, before it decays to a dark state. The lifetime measurement in RaF is benchmarked by measuring the lifetime of the $8P_{3/2}$ state in Fr to be 83(3) ns, in agreement with literature.

physics.atom-ph↗

arXiv2023

Accurate theoretical determination of the ionization potentials of CaF, SrF, and BaF

We present a comprehensive theoretical study of the ionization potentials of the MF (M= Ca, Sr, Ba) molecules using the state-of-the-art relativistic coupled cluster approach with single, double, and perturbative triple excitations (CCSD(T)). We have further corrected our results for the higher order excitations (up to full triples) and the QED self energy and vacuum polarisation contributions. We have performed an extensive investigation of the effect of the various computational parameters on the calculated ionisation potentials, which allowed us to assign realistic uncertainties on our predictions. For CaF and BaF, where precise experiments are available, our predictions are in excellent agreement with the measured values. In case of SrF, we provide a new accurate prediction of the ionisation potential that deviates from the available experimental data, motivating further experimental investigations.

physics.atom-ph↗

arXiv2023

Novel spin-precession method for sensitive EDM searches

We demonstrate a spin-precession method to observe and analyze multi-level coherence between all hyperfine levels in the $X ^2Σ^+,N=0$ ground state of barium monofluoride ($^{138}$Ba$^{19}$F). The signal is sensitive to the state-preparation Rabi frequency and external electric and magnetic fields applied in searches for a permanent electric dipole moment (EDM). In the obtained interference spectrum, the electric field and Rabi frequency become observable simultaneously with the EDM. This method reduces systematic biases and the number of auxiliary measurements for such precision measurements.

physics.atom-ph↗

arXiv2021

Ab initio calculations of the spectrum of lawrencium

Planned optical spectroscopy experiments in lawrencium (Lr, Z = 103) require accurate theoretical predictions of the location of spectral lines in order to narrow the experimental search window. We present ab initio calculations of the atomic energy levels, transition amplitudes and g-factors for lawrencium, as well as its lighter homologue lutetium (Lu, Z = 71). We use the configuration interaction with many-body perturbation-theory (CI+MBPT) method to calculate energy levels and transition properties, and benchmark the accuracy of our predicted energies using relativistic coupled-cluster codes. Our results are numerically converged and in close agreement with experimentally measured energy levels for Lu, and we expect a similar accuracy for Lr. These systematic calculations have identified multiple transitions of experimental utility and will serve to guide future experimental studies of Lr.

physics.atm-clus↗

arXiv2021

Deceleration and trapping of SrF molecules

We report on the electrostatic trapping of neutral SrF molecules. The molecules are captured from a cryogenic buffer-gas beam source into the moving traps of a 4.5 m long traveling-wave Stark decelerator. The SrF molecules in $X^2Σ^+(v=0, N=1)$ state are brought to rest as the velocity of the moving traps is gradually reduced from 190 m/s to zero. The molecules are held for up to 50 ms in multiple electric traps of the decelerator. The trapped packets have a volume (FWHM) of 1 mm$^{3}$ and a velocity spread of 5(1) m/s which corresponds to a temperature of $60(20)$ mK. Our result demonstrates a factor 3 increase in the molecular mass that has been Stark-decelerated and trapped. Heavy molecules (mass$>$100 amu) offer a highly increased sensitivity to probe physics beyond the Standard Model. This work significantly extends the species of neutral molecules of which slow beams can be created for collision studies, precision measurement and trapping experiments.

physics.atom-ph↗

arXiv2020

Nuclear Moments of Germanium Isotopes around $N$ = 40

Collinear laser spectroscopy measurements were performed on $^{69,71,73}$Ge isotopes ($Z = 32$) at ISOLDE-CERN. The hyperfine structure of the $4s^2 4p^2 \, ^3P_1 \rightarrow 4s^2 4p 5s \, ^3P_1^o$ transition of the germanium atom was probed with laser light of 269 nm, produced by combining the frequency-mixing and frequency-doubling techniques. The hyperfine fields for both atomic levels were calculated using state-of-the-art atomic relativistic Fock-space coupled-cluster calculations. A new $^{73}$Ge quadrupole moment was determined from these calculations and previously measured precision hyperfine parameters, yielding $Q_{\rm s}$ = $-$0.198(4) b, in excellent agreement with the literature value from molecular calculations. The moments of $^{69}$Ge have been revised: $μ$ = +0.920(5) $μ_{N}$ and $Q_{\rm s}$= +0.114(8) b, and those of $^{71}$Ge have been confirmed. The experimental moments around $N = 40$ are interpreted with large-scale shell-model calculations using the JUN45 interaction, revealing rather mixed wave function configurations, although their $g$-factors are lying close to the effective single-particle values. Through a comparison with neighboring isotones, the structural change from the single-particle nature of nickel to deformation in germanium is further investigated around $N = 40$.

nucl-ex↗

arXiv2020

Searches for new sources of CP violation using molecules as quantum sensors

We discuss how molecule-based searches offer complementary probes to study the violation of fundamental symmetries. These experiments have the potential to probe not only the electron EDM, but also hadronic CPV phenomena. Future experimental developments will offer generic sensitivity to probe flavor neutral sources of both leptonic and hadronic CPV at scales of $\geq$ 100 TeV, and flavor changing CPV at scales of $\geq$ 1000 TeV.

hep-ph↗

arXiv2019

Detection of the $5p-4f$ orbital crossing and its optical clock transition in Pr$^{9+}$

Recent theoretical works have proposed atomic clocks based on narrow optical transitions in highly charged ions. The most interesting candidates for searches of new physics are those which occur at rare orbital crossings where the shell structure of the periodic table is reordered. There are only three such crossings expected to be accessible in highly charged ions, and hitherto none have been observed as both experiment and theory have proven difficult. In this work we observe an orbital crossing in highly charged ions for the first time, in a system chosen to be tractable from both sides: Pr$^{9+}$. We present electron beam ion trap measurements of its spectra, including the inter-configuration lines that reveal the sought-after crossing. The proposed nHz-wide clock line, found to be at 452.334(1) nm, proceeds through hyperfine admixture of its upper state with an E2-decaying level. With state-of-the-art calculations we show that it has a very high sensitivity to new physics and extremely low sensitivity to external perturbations, making it a unique candidate for proposed precision studies.

physics.atom-ph↗

arXiv2019

High-precision ab initio calculations of the spectrum of Lr$^{+}$

The planned measurement of optical resonances in singly-ionised lawrencium (Z = 103) requires accurate theoretical predictions to narrow the search window. We present high-precision, ab initio calculations of the electronic spectra of Lr$^+$ and its lighter homologue lutetium (Z = 71). We have employed the state-of-the-art relativistic Fock space coupled cluster approach and the AMBiT CI+MBPT code to calculate atomic energy levels, g-factors, and transition amplitudes and branching-ratios. Our calculations are in close agreement with experimentally measured energy levels and transition strengths for the homologue Lu$^+$ , and are well-converged for Lr$^+$ , where we expect a similar level of accuracy. These results present the first large-scale, systematic calculations of Lr$^+$ and will serve to guide future experimental studies of this ion.

physics.atom-ph↗

arXiv2019

Lifetime Measurements of the $A^2Π_{1/2}$ and $A^2Π_{3/2}$ States in BaF

Time resolved detection of laser induced fluorescence from pulsed excitation of electronic states in barium monofluoride (BaF) molecules has been performed in order to determine the lifetimes of the $A^2Π_{1/2}$ and $A^2Π_{3/2}$ states. The method permits control over experimental parameters such that systematic biases in the interpretation of the data can be controlled to below $10^{-3}$ relative accuracy. The statistically limited values for the lifetimes of the $A^2Π_{1/2}(ν=0)$ and $A^2Π_{3/2}(ν=0)$ states are 57.1(3) ns and 47.9(7)~ns, respectively. The ratio of these values is in good agreement with scaling for the different excitation energies. The investigated molecular states are of relevance for an experimental search for a permanent electric dipole moment (EDM) of the electron in BaF.

physics.atom-ph↗