arXiv subjects

N. Huntemann

Publications and source records attributed to N. Huntemann.

At least 19 recordsLinked to original sources

arXiv2026

Lifetime of the $^2F_{7/2}$ level in Yb$^+$ for spontaneous emission of electric octupole radiation

We report a measurement of the radiative lifetime of the $^2F_{7/2}$ level of $^{171}$Yb$^+$ that is coupled to the $^2S_{1/2}$ ground state via an electric octupole transition. The radiative lifetime is determined to be $9.96(50)\times 10^7$~s, corresponding to 3.16(16) years. The result reduces the relative uncertainty in this exceptionally long excited state lifetime by one order of magnitude with respect to previous experimental estimates. Our method is based on the coherent excitation of the corresponding transition and avoids limitations through competing decay processes. The explicit dependence on the laser intensity is eliminated by simultaneously measuring the resonant Rabi frequency and the induced quadratic Stark shift. Combining the result with information on the dynamic differential polarizability permits a calculation of the transition matrix element to infer the radiative lifetime.

physics.atom-ph↗

arXiv2026

High-Resolution Spectroscopy of $^{173}$Yb$^{+}$ Ions

Compared to other stable isotopes of $\rm{Yb}^+$, $^{173}\rm{Yb}^+$ has a richer hyperfine structure, which leads to more favorable clock transitions, spectroscopic techniques for probing new physics, and more sophisticated quantum computing architectures. However, to date, its electronic spectrum remains poorly characterized. Here, we report on efficient laser cooling, state preparation, and detection of a single trapped $^{173}\rm{Yb}^+$ ion. The previously unobserved $^2\!S_{1/2} \rightarrow {}^2\!D_{3/2}$ electric quadrupole transition at 436 nm is coherently excited, and the isotope shift between $^{171}\rm{Yb}^+$ and $^{173}\rm{Yb}^+$ on this transition is determined with an uncertainty of 1.4 Hz. Using microwave spectroscopy, we resolve the hyperfine structure (HFS) of the ${}^2\!D_{3/2}$ state with a relative uncertainty below $10^{-8}$. From the HFS measurement data, we infer for ${}^{173}$Yb a nuclear magnetic octupole moment $Ω= -0.062(8)\,({\rm b} \times μ_N)$ with uncertainty reduced by more than 2 orders of magnitude compared to previous studies. The data also allow us to determine hyperfine anomalies for the ${}^2\!S_{1/2}$ and ${}^2\!D_{3/2}$ states.

physics.atom-ph↗

arXiv2025

High-accuracy multi-ion spectroscopy with mixed-species Coulomb crystals

Multi-ion optical clocks offer the possibility of overcoming the low signal-to-noise ratio of single-ion clocks, while still providing low systematic uncertainties. We present simultaneous spectroscopy of up to four ${}^{115}$In${}^+$ clock ions in a linear Coulomb crystal, sympathetically cooled with ${}^{172}$Yb${}^+$ ions. In first clock comparisons, we see agreement below $1\times10^{-17}$ with results obtained using a single In${}^+$ ion, for which we have evaluated the systematic uncertainty to be $2.5\times10^{-18}$. Operation with four clock ions reduces the instability from $1.6\times10^{-15}/\sqrt{t/(1\;\mathrm{s})}$ to $9.2\times10^{-16}/\sqrt{t/(1\;\mathrm{s})}$. We derive a model for decay-related dead time during state preparation, which matches the observed scaling of instability with clock ion number $N$, and indicates that $1/\sqrt{N}$ scaling can be achieved with the addition of a repump laser.

physics.atom-ph↗

arXiv2025

$^{115}$In$^+$-$^{172}$Yb$^+$ Coulomb crystal clock with $2.5\times10^{-18}$ systematic uncertainty

We present a scalable mixed-species Coulomb crystal clock based on the $^1S_0$ $\leftrightarrow$ $^3P_0$ transition in $^{115}$In$^+$. $^{172}$Yb$^+$ ions are co-trapped and used for sympathetic cooling. Reproducible interrogation conditions for mixed-species Coulomb crystals are ensured by a conditional preparation sequence with permutation control. We demonstrate clock operation with a 1In$^+$-3Yb$^+$ crystal, achieving a relative systematic uncertainty of $2.5\times10^{-18}$ and a relative frequency instability of $1.6\times10^{-15}/\sqrt{τ/1\;\mathrm{s}}$. We report on absolute frequency measurements with an uncertainty of $1.3\times10^{-16}$ and optical frequency comparisons with clocks based on $^{171}$Yb$^+$ (E3) and $^{87}$Sr. With a fractional uncertainty of $4.4\times10^{-18}$, the former is - to our knowledge - the most accurate frequency ratio value reported to date. For the $^{115}$In$^+$/$^{87}$Sr ratio, we improve upon the best previous measurement by more than an order of magnitude. We also demonstrate operation with four $^{115}$In$^+$ clock ions, which reduces the instability to $9.2\times10^{-16}/\sqrt{τ/1\;\mathrm{s}}$.

physics.atom-ph↗

arXiv2024

Nonlinear calcium King plot constrains new bosons and nuclear properties

Nonlinearities in King plots (KP) of isotope shifts (IS) can reveal the existence of beyond-Standard-Model (BSM) interactions that couple electrons and neutrons. However, it is crucial to distinguish higher-order Standard Model (SM) effects from BSM physics. We measure the IS of the transitions ${{}^{3}P_{0}~\rightarrow~{}^{3}P_{1}}$ in $\mathrm{Ca}^{14+}$ and ${{}^{2}S_{1/2} \rightarrow {}^{2}D_{5/2}}$ in $\mathrm{Ca}^{+}$ with sub-Hz precision as well as the nuclear mass ratios with relative uncertainties below $4\times10^{-11}$ for the five stable, even isotopes of calcium (${}^{40,42,44,46,48}\mathrm{Ca}$). Combined, these measurements yield a calcium KP nonlinearity with a significance of $\sim 900 σ$. Precision calculations show that the nonlinearity cannot be fully accounted for by the expected largest higher-order SM effect, the second-order mass shift, and identify the little-studied nuclear polarization as the only remaining SM contribution that may be large enough to explain it. Despite the observed nonlinearity, we improve existing KP-based constraints on a hypothetical Yukawa interaction for most of the new boson masses between $10~\mathrm{eV/c^2}$ and $10^7~\mathrm{eV/c^2}$.

physics.atom-ph↗

arXiv2024

Atomic photoexcitation as a tool for probing purity of twisted light modes

The twisted light modes used in modern atomic physics experiments can be contaminated by small admixtures of plane wave radiation. Although these admixtures hardly reveal themselves in the beam intensity profile, they may seriously affect the outcome of high precision spectroscopy measurements. In the present study we propose a method for diagnosing such a plane wave contamination, which is based on the analysis of the magnetic sublevel population of atoms or ions interacting with the "twisted + plane wave" radiation. In order to theoretically investigate the sublevel populations, we solve the Liouville-von Neumann equation for the time evolution of atomic density matrix. The proposed method is illustrated for the electric dipole $5s \, {}^{2}\mathrm{S}_{1/2} \, - \, 5p \, {}^{2}\mathrm{P}_{3/2}$ transition in Rb induced by (linearly, radially, or azimuthally polarized) vortex light with just a small contamination. We find that even tiny admixtures of plane wave radiation can lead to remarkable variations in the populations of the ground-state magnetic sublevels. This opens up new opportunities for diagnostics of twisted light in atomic spectroscopy experiments.

physics.atom-ph↗

arXiv2023

Improved limits on the coupling of ultralight bosonic dark matter to photons from optical atomic clock comparisons

We present improved constraints on the coupling of ultralight bosonic dark matter to photons based on long-term measurements of two optical frequency ratios. In these optical clock comparisons, we relate the frequency of the ${}^2S_{1/2} (F=0)\leftrightarrow {}^2F_{7/2} (F=3)$ electric-octupole (E3) transition in $^{171}$Yb$^{+}$ to that of the ${}^2S_{1/2} (F=0)\leftrightarrow \,{}^2D_{3/2} (F=2)$ electric-quadrupole (E2) transition of the same ion, and to that of the ${}^1S_0\leftrightarrow\,{}^3P_0$ transition in $^{87}$Sr. Measurements of the first frequency ratio $ν_\textrm{E3}/ν_\textrm{E2}$ are performed via interleaved interrogation of both transitions in a single ion. The comparison of the single-ion clock based on the E3 transition with a strontium optical lattice clock yields the second frequency ratio $ν_\textrm{E3}/ν_\textrm{Sr}$. By constraining oscillations of the fine-structure constant $α$ with these measurement results, we improve existing bounds on the scalar coupling $d_e$ of ultralight dark matter to photons for dark matter masses in the range of about $ 10^{-24}-10^{-17}\,\textrm{eV}/c^2$. These results constitute an improvement by more than an order of magnitude over previous investigations for most of this range. We also use the repeated measurements of $ν_\textrm{E3}/ν_\textrm{E2}$ to improve existing limits on a linear temporal drift of $α$ and its coupling to gravity.

physics.atom-ph↗

arXiv2022

Evaluation of a $^{88}$Sr$^+$ optical clock with a direct measurement of the blackbody radiation shift and determination of the clock frequency

We report on an evaluation of an optical clock that uses the $\phantom{}^2S_{1/2} \rightarrow \phantom{}^2D_{5/2}$ transition of a single $^{88}$Sr$^+$ ion as the reference. In contrast to previous work, we estimate the effective temperature of the blackbody radiation that shifts the reference transition directly during operation from the corresponding frequency shift and the well-characterized sensitivity to thermal radiation. We measure the clock output frequency against an independent $^{171}$Yb$^+$ ion clock, based on the $\phantom{}^2S_{1/2} (F=0) \rightarrow \phantom{}^2F_{7/2} (F=3)$ electric octupole (E3) transition, and determine the frequency ratio with a total fractional uncertainty of $2.3\times 10^{-17}$. Relying on a previous measurement of the $^{171}$Yb$^+$ (E3) clock frequency, we find the absolute frequency of the $^{88}$Sr$^+$ clock transition to be $444779044095485.271(59)\,\text{Hz}$. Our result reduces the uncertainty by a factor of $3$ compared to the previously most accurate measurement and may help to resolve so far inconsistent determinations of this value. We also show that for three simultaneously interrogated $^{88}$Sr$^+$ ions, the increased number causes the expected improvement of the short-term frequency instability of the optical clock without degrading its systematic uncertainty.

physics.atom-ph↗

arXiv2021

Improved limits for violations of local position invariance from atomic clock comparisons

We compare two optical clocks based on the $^2$S$_{1/2}(F=0)\to {}^2$D$_{3/2}(F=2)$ electric quadrupole (E2) and the $^2$S$_{1/2}(F=0)\to {}^2$F$_{7/2}(F=3)$ electric octupole (E3) transition of $^{171}$Yb$^{+}$ and measure the frequency ratio $ν_{\mathrm{E3}}/ν_{\mathrm{E2}}=0.932\,829\,404\,530\,965\,376(32)$. We determine the transition frequency $ν_{E3}=642\,121\,496\,772\,645.10(8)$ Hz using two caesium fountain clocks. Repeated measurements of both quantities over several years are analyzed for potential violations of local position invariance. We improve by factors of about 20 and 2 the limits for fractional temporal variations of the fine structure constant $α$ to $1.0(1.1)\times10^{-18}/\mathrm{yr}$ and of the proton-to-electron mass ratio $μ$ to $-8(36)\times10^{-18}/\mathrm{yr}$. Using the annual variation of the Sun's gravitational potential at Earth $Φ$, we improve limits for a potential coupling of both constants to gravity, $(c^2/α) (dα/dΦ)=14(11)\times 10^{-9}$ and $(c^2/μ) (dμ/dΦ)=7(45)\times 10^{-8}$.

physics.atom-ph↗

arXiv2020

Coherent suppression of tensor frequency shifts through magnetic field rotation

We introduce a scheme to coherently suppress second-rank tensor frequency shifts in atomic clocks, relying on the continuous rotation of an external magnetic field during the free atomic state evolution in a Ramsey sequence. The method retrieves the unperturbed frequency within a single interrogation cycle and is readily applicable to various atomic clock systems. For the frequency shift due to the electric quadrupole interaction, we experimentally demonstrate suppression by more than two orders of magnitude for the ${}^2S_{1/2} \to {}^2D_{3/2}$ transition of a single trapped ${}^{171}\text{Yb}^+$ ion. The scheme provides particular advantages in the case of the ${}^{171}\text{Yb}^+$ ${}^2S_{1/2} \to {}^2F_{7/2}$ electric octupole (E3) transition. For an improved estimate of the residual quadrupole shift for this transition, we measure the excited state electric quadrupole moments $Θ({}^2D_{3/2}) = 1.95(1)~ea_0^2$ and $Θ({}^2F_{7/2}) = -0.0297(5)~ea_0^2$ with $e$ the elementary charge and $a_0$ the Bohr radius, improving the measurement uncertainties by one order of magnitude.

physics.atom-ph↗

arXiv2020

Generalized excitation of atomic multipole transitions by twisted light modes

A theoretical study is performed for the excitation of a single atom localized in the center of twisted light modes. Here we present the explicit dependence of excitation rates on critical parameters, such as the polarization of light, its orbital angular momentum projection, and the orientation of its propagation axis with respect to the atomic quantization axis. The effect of a spatial spread of the atom is also considered in detail. The expressions for transition rates obtained in this work can be used for any atom of arbitrary electronic configuration. For definiteness we apply them to the specific case of $^{2}S_{1/2} (F=0) \rightarrow\; ^{2}F_{7/2} (F=3, M=0)$ electric octupole (E3) transition in $^{171}$Yb$^{+}$ ion. Our analytical and numerical results are suitable for the analysis and planning of future experiments on the excitation of electric-dipole-forbidden transitions by twisted light modes in optical atomic clocks.

physics.atom-ph↗

arXiv2019

Direct comparisons of European primary and secondary frequency standards via satellite techniques

We carried out a 26-day comparison of five simultaneously operated optical clocks and six atomic fountain clocks located at INRIM, LNE-SYRTE, NPL and PTB by using two satellite-based frequency comparison techniques: broadband Two-Way Satellite Time and Frequency Transfer (TWSTFT) and Global Positioning System Precise Point Positioning (GPS PPP). With an enhanced statistical analysis procedure taking into account correlations and gaps in the measurement data, combined overall uncertainties in the range of $1.8 \times 10^{-16}$ to $3.5 \times 10^{-16}$ for the optical clock comparisons were found. The comparison of the fountain clocks yields results with a maximum relative frequency difference of $6.9 \times 10^{-16}$, and combined overall uncertainties in the range of $4.8 \times 10^{-16}$ to $7.7 \times 10^{-16}$.

physics.ins-det↗

arXiv2019

Search for transient variations of the fine structure constant and dark matter using fiber-linked optical atomic clocks

We search for transient variations of the fine structure constant using data from a European network of fiber-linked optical atomic clocks. By searching for coherent variations in the recorded clock frequency comparisons across the network, we significantly improve the constraints on transient variations of the fine structure constant. For example, we constrain the variation in alpha to <5*10^-17 for transients of duration 10^3 s. This analysis also presents a possibility to search for dark matter, the mysterious substance hypothesised to explain galaxy dynamics and other astrophysical phenomena that is thought to dominate the matter density of the universe. At the current sensitivity level, we find no evidence for dark matter in the form of topological defects (or, more generally, any macroscopic objects), and we thus place constraints on certain potential couplings between the dark matter and standard model particles, substantially improving upon the existing constraints, particularly for large (>~10^4 km) objects.

astro-ph.CO↗

arXiv2016

Single-Ion Atomic Clock with $3\times10^{-18}$ Systematic Uncertainty

We experimentally investigate an optical frequency standard based on the $^2S_{1/2} (F=0)\to {}^2F_{7/2} (F=3)$ electric octupole (\textit{E}3) transition of a single trapped $^{171}$Yb$^+$ ion. For the spectroscopy of this strongly forbidden transition, we utilize a Ramsey-type excitation scheme that provides immunity to probe-induced frequency shifts. The cancellation of these shifts is controlled by interleaved single-pulse Rabi spectroscopy which reduces the related relative frequency uncertainty to $1.1\times 10^{-18}$. To determine the frequency shift due to thermal radiation emitted by the ion's environment, we measure the static scalar differential polarizability of the \textit{E}3 transition as $0.888(16)\times 10^{-40}$ J m$^2$/V$^2$ and a dynamic correction $η(300~\text{K})=-0.0015(7)$. This reduces the uncertainty due to thermal radiation to $1.8\times 10^{-18}$. The residual motion of the ion yields the largest contribution $(2.1\times 10^{-18})$ to the total systematic relative uncertainty of the clock of $3.2\times 10^{-18}$.

physics.atm-clus↗

arXiv2015

Frequency comparison of ${}^{171}$Yb${}^+$ ion optical clocks at PTB and NPL via GPS PPP

We used Precise Point Positioning, a well-established GPS carrier-phase frequency transfer method to perform a direct remote comparison of two optical frequency standards based on single laser-cooled $^{171}$Yb$^+$ ions operated at NPL, UK and PTB, Germany. At both institutes an active hydrogen maser serves as a flywheel oscillator; it is connected to a GPS receiver as an external frequency reference and compared simultaneously to a realization of the unperturbed frequency of the ${{}^2S_{1/2}(F=0)-{}^2D_{3/2}(F=2)}$ electric quadrupole transition in ${}^{171}$Yb${}^+$ via an optical femtosecond frequency comb. To profit from long coherent GPS link measurements we extrapolate over the various data gaps in the optical clock to maser comparisons which introduces maser noise to the frequency comparison but improves the uncertainty from the GPS link. We determined the total statistical uncertainty consisting of the GPS link uncertainty and the extrapolation uncertainties for several extrapolation schemes. Using the extrapolation scheme with the smallest combined uncertainty, we find a fractional frequency difference $y(\mathrm{PTB})-y(\mathrm{NPL})$ of $-1.3(1.2)\times 10^{-15}$ for a total measurement time of 67 h. This result is consistent with an agreement of both optical clocks and with recent absolute frequency measurements against caesium fountain clocks.

physics.atom-ph↗

arXiv2015

Phase Analysis for Frequency Standards in the Microwave and Optical Domains

Coherent manipulation of atomic states is a key concept in high-precision spectroscopy and used in atomic fountain clocks and a number of optical frequency standards. Operation of these standards can involve a number of cyclic switching processes, which may induce cycle synchronous phase excursions of the interrogation signal and thus lead to shifts in the output of the frequency standard. We have built a FPGA-based phase analyzer to investigate these effects and conducted measurements on two frequency standards. For the caesium fountain PTB-CSF2 we were able to exclude phase variations of the microwave source at the level of a few $μ$rad, corresponding to relative frequency shifts of less than 10$^{-16}$. In the optical domain, we investigated phase variations in PTB's Yb$^+$ optical frequency standard and made detailed measurements of AOM chirps and their scaling with duty cycle and driving power. We ascertained that cycle-synchronous as well as long-term phase excursion do not cause frequency shifts larger than 10$^{-18}$.

physics.atom-ph↗

arXiv2014

Improved limit on a temporal variation of $m_p/m_e$ from comparisons of Yb$^+$ and Cs atomic clocks

Accurate measurements of different transition frequencies between atomic levels of the electronic and hyperfine structure over time are used to investigate temporal variations of the fine structure constant $α$ and the proton-to-electron mass ratio $μ$. We measure the frequency of the $^2S_{1/2}\rightarrow {^2F_{7/2}}$ electric octupole (E3) transition in $^{171}$Yb$^+$ against two caesium fountain clocks as $f(E3) = 642\,121\,496\,772\,645.36(25)$~Hz with an improved fractional uncertainty of $3.9\times 10^{-16}$. This transition frequency shows a strong sensitivity to changes of $α$. Together with a number of previous and recent measurements of the $^2S_{1/2}\rightarrow {^2D_{3/2}}$ electric quadrupole transition in $^{171}$Yb$^+$ and with data from other elements, a least-squares analysis yields $(1/α)(dα/dt)=-0.20(20)\times 10^{-16}/\mathrm{yr}$ and $(1/μ)(dμ/dt)=-0.5(1.6)\times 10^{-16}/\mathrm{yr}$, confirming a previous limit on $dα/dt$ and providing the most stringent limit on $d μ/dt$ from laboratory experiments.

physics.atom-ph↗

arXiv2014

Direct comparison of optical lattice clocks with an intercontinental baseline of 9 000 km

We have demonstrated a direct frequency comparison between two $^{87}{\rm Sr}$ lattice clocks operated in intercontinentally separated laboratories in real time. Two-way satellite time and frequency transfer technique based on the carrier phase was employed for a direct comparison with a baseline of 9 000 km between Japan and Germany. A clock comparison was achieved for 83 640 s resulting in a fractional difference of $(1.1\pm1.6) \times 10^{-15}$, where the statistical part is the biggest contribution to the uncertainty. This measurement directly confirms the agreement of the two optical clocks on an intercontinental scale.

physics.atom-ph↗