arXiv subjects

Wilfried Nörtershäuser

Publications and source records attributed to Wilfried Nörtershäuser.

28 records · Page 2Linked to original sources

arXiv2020

Raman velocity filter as a tool for collinear laser spectroscopy

The velocity distribution of a hot ionic beam can be filtered with a narrow stimulated Raman process to prepare a colder subensemble, as substantiated in this theoretical analysis. Using two counter-propagating, far-detuned lasers, we can define a $π$-pulse for the resonant velocity to transfer atoms within the linewidth of the Raman resonance between the ground-states of a $Λ$-system. Spontaneous emission from the two single-photon resonances, as well as the ground-state decoherence induced by laser noise, diminishes the efficiency of the filter. From a comprehensive master equation, we obtain conditions for the optimal frequency pair of the lasers and evaluate the filter performance numerically, as well as analytically. If we apply this analysis to current $^{40}$Ca$^+$ ion experiments, we obtain a sensitivity for measuring high ion acceleration voltages on the ppm level or below.

physics.atom-ph↗

arXiv2019

Lifetimes and g-factors of the HFS states in H-like and Li-like bismuth

The LIBELLE experiment performed at the experimental storage ring (ESR) at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, Germany, has successfully determined the ground state hyperfine (HFS) splittings in hydrogen-like ($^{209}\rm{Bi}^{82+}$) and lithium-like ($^{209}\rm{Bi}^{80+}$) bismuth. The study of HFS transitions in highly charged ions enables precision tests of QED in extreme electric and magnetic fields otherwise not attainable in laboratory experiments. Besides the transition wavelengths the time resolved detection of fluorescence photons following the excitation of the ions by a pulsed laser system also allows to extract lifetimes of the upper HFS levels and g-factors of the bound 1s and 2s electrons for both charge states. While the lifetime of the upper HFS state in $^{209}\rm{Bi}^{82+}$ has already been measured in earlier experiments, an experimental value for lifetime of this state in $^{209}\rm{Bi}^{80+}$ is reported for the first time in this work.

physics.atom-ph↗

arXiv2019

Nuclear Charge Radii of $^{10,11}$B

The first determination of the nuclear charge radius by laser spectroscopy for a five-electron system is reported. This is achieved by combining high-accuracy ab initio mass-shift calculations and a high-resolution measurement of the isotope shift in the $2s^2 2p\, ^2\mathrm{P}_{1/2} \rightarrow 2s^2 3s\, ^2\mathrm{S}_{1/2}$ ground state transition in boron atoms. Accuracy is increased by orders of magnitude for the stable isotopes $^{10,11}$B and the results are used to extract their difference in the mean-square charge radius $\langle r^2_\mathrm{c}\rangle^{11} - \langle r^2_\mathrm{c}\rangle^{10} = -0.49\,(12)\,\mathrm{fm}^2$. The result is qualitatively explained by a possible cluster structure of the boron nuclei and quantitatively used as a benchmark for new ab initio nuclear structure calculations using the no-core shell model and Green's function Monte Carlo approaches.

physics.atom-ph↗

arXiv2018

New Nuclear Magnetic Moment of $^{209}$Bi - Resolving the Bismuth Hyperfine Puzzle

A recent measurement of the hyperfine splitting in the ground state of Li-like $^{209}$Bi$^{80+}$ has established a "hyperfine puzzle" -- the experimental result exhibits a 7$σ$ deviation from the theoretical prediction [J. Ullmann et al., Nat. Commun. 8, 15484 (2017); J. P. Karr, Nat. Phys. 13, 533 (2017)]. We provide evidence that the discrepancy is caused by an inaccurate value of the tabulated nuclear magnetic moment ($μ_I$) of $^{209}$Bi. We perform relativistic density functional theory and relativistic coupled cluster calculations of the shielding constant that should be used to extract the value of $μ_I(^{209}{\rm Bi})$ and combine it with nuclear magnetic resonance measurements of Bi(NO$_3$)$_3$ in nitric acid solutions and of the hexafluoridobismuthate(V) BiF$_6^-$ ion in acetonitrile. The result clearly reveals that $μ_I(^{209}{\rm Bi})$ is much smaller than the tabulated value used previously. Applying the new magnetic moment shifts the theoretical prediction into agreement with experiment and resolves the hyperfine puzzle.

physics.atom-ph↗

arXiv2015

Precision Test of Many-Body QED in the Be$^+$ $2p$ Fine Structure Doublet Using Short-Lived Isotopes

Absolute transition frequencies of the $2s\; ^2{\rm S}_{1/2} \rightarrow 2p\;^2\mathrm{P}_{1/2,3/2}$ transitions in Be$^+$ were measured for the isotopes $^{7,9-12}$Be. The fine structure splitting of the $2p$ state and its isotope dependence are extracted and compared to results of \textit{ab initio} calculations using explicitly correlated basis functions, including relativistic and quantum electrodynamics effects at the order of $m α^6$ and $m α^7 \ln α$. Accuracy has been improved in both the theory and experiment by 2 orders of magnitude, and good agreement is observed. This represents one of the most accurate tests of quantum electrodynamics for many-electron systems, being insensitive to nuclear uncertainties.

physics.atom-ph↗

arXiv2015

Collinear laser spectroscopy of atomic cadmium

Hyperfine structure $A$ and $B$ factors of the atomic $5s\,5p\,\; ^3\rm{P}_2 \rightarrow 5s\,6s\,\; ^3\rm{S}_1$ transition are determined from collinear laser spectroscopy data of $^{107-123}$Cd and $^{111m-123m}$Cd. Nuclear magnetic moments and electric quadrupole moments are extracted using reference dipole moments and calculated electric field gradients, respectively. The hyperfine structure anomaly for isotopes with $s_{1/2}$ and $d_{5/2}$ nuclear ground states and isomeric $h_{11/2}$ states is evaluated and a linear relationship is observed for all nuclear states except $s_{1/2}$. This corresponds to the Moskowitz-Lombardi rule that was established in the mercury region of the nuclear chart but in the case of cadmium the slope is distinctively smaller than for mercury. In total four atomic and ionic levels were analyzed and all of them exhibit a similar behaviour. The electric field gradient for the atomic $5s\,5p\,\; ^3\mathrm{P}_2$ level is derived from multi-configuration Dirac-Hartree-Fock calculations in order to evaluate the spectroscopic nuclear quadrupole moments. The results are consistent with those obtained in an ionic transition and based on a similar calculation.

nucl-ex↗

arXiv2014

Observation of the hyperfine transition in lithium-like Bismuth $^{209}\text{Bi}^{80+}$: Towards a test of QED in strong magnetic fields

We performed a laser spectroscopic determination of the $2s$ hyperfine splitting (HFS) of Li-like $^{209}\text{Bi}^{80+}$ and repeated the measurement of the $1s$ HFS of H-like $^{209}\text{Bi}^{82+}$. Both ion species were subsequently stored in the Experimental Storage Ring at the GSI Helmholtzzentrum für Schwerionenforschung Darmstadt and cooled with an electron cooler at a velocity of $\approx 0.71\,c$. Pulsed laser excitation of the $M1$ hyperfine-transition was performed in anticollinear and collinear geometry for $\text{Bi}^{82+}$ and $\text{Bi}^{80+}$, respectively, and observed by fluorescence detection. We obtain $ΔE^{(1s)}= 5086.3(11)\,\textrm{meV}$ for $\text{Bi}^{82+}$, different from the literature value, and $ΔE^{(2s)}= 797.50(18)\,\textrm{meV}$ for $\text{Bi}^{80+}$. These values provide experimental evidence that a specific difference between the two splitting energies can be used to test QED calculations in the strongest static magnetic fields available in the laboratory independent of nuclear structure effects. The experimental result is in excellent agreement with the theoretical prediction and confirms the sum of the Dirac term and the relativistic interelectronic-interaction correction at a level of 0.5% confirming the importance of accounting for the Breit interaction.

physics.atom-ph↗

arXiv2014

Test of Time Dilation Using Stored Li+ Ions as Clocks at Relativistic Speed

We present the concluding result from an Ives-Stilwell-type time dilation experiment using 7Li+ ions confined at a velocity of beta = v/c = 0.338 in the storage ring ESR at Darmstadt. A Lambda-type three-level system within the hyperfine structure of the 7Li+ triplet S1-P2 line is driven by two laser beams aligned parallel and antiparallel relative to the ion beam. The lasers' Doppler shifted frequencies required for resonance are measured with an accuracy of < 4 ppb using optical-optical double resonance spectroscopy. This allows us to verify the Special Relativity relation between the time dilation factor gamma and the velocity beta to within 2.3 ppb at this velocity. The result, which is singled out by a high boost velocity beta, is also interpreted within Lorentz Invariance violating test theories.

physics.atom-ph↗

arXiv2012

Precision Atomic Physics Techniques for Nuclear Physics with Radioactive Beams

Atomic physics techniques for the determination of ground-state properties of radioactive isotopes are very sensitive and provide accurate masses, binding energies, Q-values, charge radii, spins, and electromagnetic moments. Many fields in nuclear physics benefit from these highly accurate numbers. They give insight into details of the nuclear structure for a better understanding of the underlying effective interactions, provide important input for studies of fundamental symmetries in physics, and help to understand the nucleosynthesis processes that are responsible for the observed chemical abundances in the Universe. Penning-trap and and storage-ring mass spectrometry as well as laser spectroscopy of radioactive nuclei have now been used for a long time but significant progress has been achieved in these fields within the last decade. The basic principles of laser spectroscopic investigations, Penning-trap and storage-ring mass measurements of short-lived nuclei are summarized and selected physics results are discussed.

physics.atom-ph↗

arXiv2012

Nuclear Charge Radius of $^{12}$Be

The nuclear charge radius of $^{12}$Be was precisely determined using the technique of collinear laser spectroscopy on the $2s_{1/2}\rightarrow 2p_{1/2, 3/2}$ transition in the Be$^{+}$ ion. The mean square charge radius increases from $^{10}$Be to $^{12}$Be by $δ ^{10,12} = 0.69(5) \fm^{2}$ compared to $δ ^{10,11} = 0.49(5) \fm^{2}$ for the one-neutron halo isotope $^{11}$Be. Calculations in the fermionic molecular dynamics approach show a strong sensitivity of the charge radius to the structure of $^{12}$Be. The experimental charge radius is consistent with a breakdown of the N=8 shell closure.

physics.atom-ph↗