arXiv subjects

J. Rahm

Publications and source records attributed to J. Rahm.

7 recordsLinked to original sources

arXiv2025

$^{88}$Sr$^{+}$ optical clock with $7.9\times 10^{-19}$ systematic uncertainty and measurement of its absolute frequency with $9.8\times 10^{-17}$ uncertainty

We report on a $^{88}$Sr$^{+}$ single-ion optical clock with an estimated fractional systematic uncertainty of $7.9\times 10^{-19}$. The low uncertainty is enabled by small rf losses, a thorough evaluation of the blackbody-radiation temperature, and our recent measurement of the differential polarizability. A detailed uncertainty evaluation is presented. We also report on two absolute frequency measurements: one against a remote cesium fountain clock and one against International Atomic Time (TAI). The former lasted 12 days and resulted in a frequency value of 444779044095485.49(15) Hz. The latter spanned ten months with monthly optical-clock uptimes between 68% and 99% and yielded a frequency value of 444779044095485.373(44) Hz. With a fractional uncertainty of $9.8\times 10^{-17}$, it is, to our knowledge, the most accurate optical frequency measurement reported to date. Both frequency values are in agreement with other recent measurements, providing further evidence that the 2021 CIPM recommended frequency value is too high by 1.6 times its uncertainty.

physics.atom-ph↗

arXiv2025

Transportable strontium lattice clock with $4 \times 10^{-19}$ blackbody radiation shift uncertainty

We describe a transportable optical lattice clock based on the $^1\mathrm{S}_0 \rightarrow {^3\mathrm{P}_0}$ transition of lattice-trapped $^{87}$Sr atoms with a total systematic uncertainty of $2.1 \times 10^{-18}$. The blackbody radiation shift, which is the leading systematic effect in many strontium lattice clocks, is controlled at the level of $4.0 \times 10^{-19}$, as the atoms are interrogated inside a well-characterised, cold thermal shield. Using a transportable clock laser, the clock reaches a frequency instability of about $5 \times 10^{-16}/\sqrt{\tau/\mathrm{s}}$, which enables fast reevaluations of systematic effects. By comparing this clock to the primary caesium fountain clocks CSF1 and CSF2 at Physikalisch-Technische Bundesanstalt, we measure the clock transition frequency with a fractional uncertainty of $1.9\times 10^{-16}$, in agreement with previous results. The clock was successfully transported and operated at different locations. It holds the potential to be used for geodetic measurements with centimetre-level or better height resolution and for accurate inter-institute frequency comparisons.

physics.atom-ph↗

arXiv2024

$^{115}$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 $1.6\times10^{-15}/\sqrt{\tau/1\;\mathrm{s}}$. 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 $9.2\times10^{-16}/\sqrt{\tau/1\;\mathrm{s}}$.

physics.atom-ph↗

arXiv2020

Long term measurement of the $^{87}$Sr clock frequency at the limit of primary Cs clocks

We report on a series of 42 measurements of the transition frequency of the 429~THz (5s$^2$)~$^1$S$_0$--(5s5p)~$^3$P$_0$ line in $^{87}$Sr taken over three years from 2017 to 2019. They have been performed at the Physikalisch-Technische Bundesanstalt (PTB) between the laboratory strontium lattice clock and the primary caesium fountain clocks CSF1 and CSF2. The length of each individual measurement run has been extended by use of a hydrogen maser as flywheel to improve the statistical uncertainty given by the Cs clocks. We determine an averaged transition frequency of $429\:228\:004\:229\:873.00(0.07)$~Hz with $1.5\times10^{-16}$ fractional uncertainty, at the limit of the current realization of the unit hertz. Analysis of the data provides an improved limit on the coupling of the gravitational potential of the Sun to the proton--electron mass ratio $\mu$, and confirms the limits on its temporal drift.

physics.atom-ph↗

arXiv2018

Advances in the accuracy, stability, and reliability of the PTB primary fountain clocks

Improvements of the systematic uncertainty, frequency instability, and long-term reliability of the two caesium fountain primary frequency standards CSF1 and CSF2 at PTB (Physikalisch-Technische Bundesanstalt) are described. We have further investigated many of the systematic effects and made a number of modifications of the fountains. With an optically stabilized microwave oscillator, the quantum projection noise limited frequency instabilities are improved to $7.2 \times 10^{-14} (\tau/1\,\mathrm{s})^{-1/2}$ for CSF1 and $2.5 \times 10^{-14} (\tau/1\,\mathrm{s})^{-1/2}$ for CSF2 at high atom density. The systematic uncertainties of CSF1 and CSF2 are reduced to $2.74 \times 10^{-16}$ and $1.71 \times 10^{-16}$, respectively. Both fountain clocks regularly calibrate the scale unit of International Atomic Time (TAI) and the local realization of Coordinated Universal Time, UTC(PTB), and serve as references to measure the frequencies of local and remote optical frequency standards.

physics.atom-ph↗

arXiv1998

Precise strength of th piNN coupling constant

We report here a preliminary value for the piNN coupling constant deduced from the GMO sumrule for forward piN scattering. As in our previous determination from np backward differential scattering cross sections we give a critical discussion of the analysis with careful attention not only to the statistical, but also to the systematic uncertainties. Our preliminary evaluation gives $g^2_c$(GMO) = 13.99(24).

hep-ph↗

arXiv1998

The Pion-Nucleon coupling constant from np charge exchange scattering

A novel extrapolation method has been used to deduce the charged Pion-Nucleon coupling constant from backward $np$ differential scattering cross sections. We applied it to new measurements performed at 162 MeV at the The Svedberg Laboratory in Uppsala. In the angular range $150^\circ-180^\circ$, the carefully normalized data are steeper than those of most previous measurements. The extracted value, $g^2_{π^\pm} = 14.52 \pm 0.26$, in good agreement with the classical value, is higher than those determined in recent nucleon-nucleon partial-wave analyses.

nucl-th↗