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Register a new userImproved limit on a temporal variation of $m_p/m_e$ from comparisons of Yb$^+$ and Cs atomic clocks
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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 $alpha$ and the proton-to-electron mass ratio $mu$. 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 $3.9times 10^{-16}$. This transition frequency shows a strong sensitivity to changes of $alpha$. 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 $(1/alpha)(dalpha/dt)=-0.20(20)times 10^{-16}/mathrm{yr}$ and $(1/mu)(dmu/dt)=-0.5(1.6)times 10^{-16}/mathrm{yr}$, confirming a previous limit on $dalpha/dt$ and providing the most stringent limit on $d mu/dt$ from laboratory experiments.
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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 $ u_{mathrm{E3}}/ u_{mathrm{E2}}=0.932,829,404,530,965,376(32)$. We determine the transition frequency $ u_{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 $alpha$ to $1.0(1.1)times10^{-18}/mathrm{yr}$ and of the proton-to-electron mass ratio $mu$ to $-8(36)times10^{-18}/mathrm{yr}$. Using the annual variation of the Suns gravitational potential at Earth $Phi$, we improve limits for a potential coupling of both constants to gravity, $(c^2/alpha) (dalpha/dPhi)=14(11)times 10^{-9}$ and $(c^2/mu) (dmu/dPhi)=7(45)times 10^{-8}$.
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 $1.5times10^{-16}$ 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.
We report the production of ultracold heteronuclear Cs$^*$Yb molecules through one-photon photoassociation applied to an ultracold atomic mixture of Cs and Yb confined in an optical dipole trap. We use trap-loss spectroscopy to detect molecular states below the Cs($^{2}P_{1/2}$) + Yb($^{1}S_{0}$) asymptote. For $^{133}$Cs$^{174}$Yb, we observe 13 rovibrational states with binding energies up to $sim$500 GHz. For each rovibrational state we observe two resonances associated with the Cs hyperfine structure and show that the hyperfine splitting in the diatomic molecule decreases for more deeply bound states. In addition, we produce ultracold fermionic $^{133}$Cs$^{173}$Yb and bosonic $^{133}$Cs$^{172}$Yb and $^{133}$Cs$^{170}$Yb molecules. From mass scaling, we determine the number of bound states supported by the 2(1/2) excited-state potential to be 154 or 155.
In the last ten years extraordinary results in time and frequency metrology have been demonstrated. Frequency-stabilization techniques for continuous-wave lasers and femto-second optical frequency combs have enabled a rapid development of frequency standards based on optical transitions in ultra-cold neutral atoms and trapped ions. As a result, todays best performing atomic clocks tick at an optical rate and allow scientists to perform high-resolution measurements with a precision approaching a few parts in $10^{18}$. This paper reviews the history and the state of the art in optical-clock research and addresses the implementation of optical clocks in a possible future redefinition of the SI second as well as in tests of fundamental physics.
Atomic clocks use atomic transitions as frequency references. The susceptibility of the atomic transition to external fields limits clock stability and introduces systematic frequency shifts. Here, we propose to realize an atomic clock that utilizes an entangled superposition of states of multiple atomic species, where the reference frequency is a sum of the individual transition frequencies. The superposition is selected such that the susceptibilities of the respective transitions, in individual species, destructively interfere leading to improved stability and reduced systematic shifts. We present and analyze two examples of such combinations. The first uses the optical quadrupole transitions in a $^{40}$Ca$^+$ - $^{174}$Yb$^+$ two-ion crystal. The second is a superposition of optical quadrupole transitions in one $^{88}$Sr$^+$ ion and three $^{202}$Hg$^+$ ions. These combinations have reduced susceptibility to external magnetic fields and blackbody radiation.
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