Optical atomic clocks based on trapped ions suffer from systematic frequency shifts of the clock transition due to interaction with blackbody radiation from the environment. These shifts can be compensated if the blackbody radiation spectrum and the differential dynamic polarizability is known to a sufficient precision. Here, we present a new measurement scheme, based on quantum logic that allows a direct transfer of precision for polarizability measurements from one species to the other. This measurement circumvents the necessity of calibrating laser power below the percent level, which is the limitation for state-of-the-art polarizability measurements in trapped ions. Furthermore, the presented technique allows one to reference the polarizability transfer to hydrogenlike ions for which the polarizability can be calculated with high precision.
Optical atomic clocks based on trapped ions suffer from systematic frequency shifts of the clock transition due to interaction with blackbody radiation from the environment. These shifts can be compensated if the blackbody radiation spectrum and the differential dynamic polarizability is known to a sufficient precision. Here, we present a new measurement scheme, based on quantum logic that allows a direct transfer of precision for polarizability measurements from one species to the other. This measurement circumvents the necessity of calibrating laser power below the percent level, which is the limitation for state-of-the-art polarizability measurements in trapped ions. Furthermore, the presented technique allows one to reference the polarizability transfer to hydrogenlike ions for which the polarizability can be calculated with high precision.
A modification to a successfull technique to measure static differential polarizabilities of ultracold atoms and molecules is presented. Ultracold atoms are trapped in a magic wavelength optical lattice and transported into the field of a precision capacitor. The change of the transition frequency induced by the applied field, which is controlled to better than 10-4, is measured. For atomic clocks, the difference of the static polarizabilies of ground and excited state is closely related to their response to a blackbody radiation field, which is a significant contribution to the uncertainty budget of many atomic clocks.
Presently, the Stark effect contributes the largest source of uncertainty in a ytterbium optical atomic clock through blackbody radiation. By employing an ultracold, trapped atomic ensemble and high stability optical clock, we characterize the quadratic Stark effect with unprecedented precision. We report the ytterbium optical clock's sensitivity to electric fields (such as blackbody radiation) as the differential static polarizability of the ground and excited clock levels ${\ensuremath{\alpha}}_{\mathrm{clock}}=36.2612(7)\text{ }\text{ }\mathrm{kHz}\text{ }(\mathrm{kV}/\mathrm{cm}{)}^{\ensuremath{-}2}$. The clock's uncertainty due to room temperature blackbody radiation is reduced by an order of magnitude to $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}$.
It is shown that the dynamic differential scalar polarizability of the ${S}_{1/2}\ensuremath{-}{D}_{5/2}$ transition in 138Ba+ can be determined to an inaccuracy below 0.5 across a wide wavelength range ($\ensuremath{\lambda}>700\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$). This can be achieved using measurements for which accurate determination of laser intensity is not required, and most of the required measurements are already in the literature. Measurement of a laser-induced ac-Stark shift of the clock transition would then provide an in situ measurement of the laser's intensity to the same 0.5 level of inaccuracy, which is not easily achieved by other means. This would allow accurate polarizability measurements for clock transitions in other ions, through comparison with 138Ba+. The approach would be equally applicable to Sr+ and Ca+, with the latter being immediately applicable to Al+/Ca+ quantum logic clocks.
Ytterbium lattice frequency standard is an outstanding optical clock with a demonstrated relative frequency accuracy of 3.4·10-16, presently limited by the uncertainty on the blackbody radiation (BBR), lattice polarizabilities and cold collisions shifts. In particular the BBR shift is looming as a major component in the uncertainty budget of many optical frequency standards. In fact the uncertainty on BBR systematic shift in Ytterbium atoms is due both to experimental and theoretical limits in the knowledge of the atomic system: presently Ytterbium has the largest theoretical uncertainty on the BBR shift. Then, both for atomic physics and metrology, new measurements of the Ytterbium atomic properties are strongly demanded, such as the determination of transition matrix elements, lifetimes, branching ratios, polarizabilities and hyperfine constants. In this work we present a set of new measurements for the radiative decay and for the cold collisions trap losses in laser-cooled Ytterbium atoms. These data are relevant to the blackbody radiation shift evaluation and to the cold collisions shift theory.
Frequency standards based on optical transitions between electronic states of trapped ions have reached uncertainties below 10−18 [1]. The Stark shift caused by room-temperature blackbody radiation (BBR) causes the largest correction for most high-performance optical clock. The systematic uncertainty of 171Yb+ clocks based on the 2S1/2 (F = 0) → 2D3/2 (F = 2) electric quadrupole (E2) and 2S1/2 (F = 0) → 2F7/2 (F = 3) electric octupole (E3) transitions is currently limited to 28×10−18 and 1.5×10−18, respectively, by the fractional accuracy of the differential polarizability Δαdc of approximately 2% [2]. In the scope of this thesis, a dual species clock based on 171Yb+ and 88Sr+ ions was set up, operated and evaluated, to overcome this barrier. Since Δαdc is known with a smaller fractional uncertainty of 0.04% for the 2S1/2 → 2D5/2 E2 transition of 88Sr+ [3], this allows for a transfer of Δαdc from 88Sr+ to 171Yb+ following a method proposed in [4]. The optical intensity of a laser is calibrated with the Stark shift it causes on the 88Sr+ clock transition, allowing for the determination of Δαdc of the 171Yb+ clock transitions. This allows for a reduction of the fractional uncertainty of Δαdc for both 171Yb+ clock transitions below 0.4% and clock operation on the E2 and E3 transition with a fractional BBR shift uncertainty of 0.84×10−18 and 0.24×10−18 is enabled, respectively. However the value of Δαdc determined in this thesis does not agree with [2], a fractional offset of approximately 14% is observed. To investigate this discrepancy further, Δαdc is measured in the same manner as in [2] for the 88Sr+ clock transition. The same offset of approximately 14% is found, calling the accuracy of at least one of these methods into question. Finally, the first optical frequency ratio ℛ between the 88Sr+ clock transition and the 171Yb+ E3 transition is measured. The fractional uncertainty of ℛ is 23×10−18. ℛ in combination with the absolute frequency of the E3 transition allows for the determination of the 88Sr+ absolute frequency νSr+ with an uncertainty limited by the caesium references. The value of νSr+ falls outside of the recommended range, but is corroborated by measurements of the same quantity by other institutes [5, 6]. [1] M. Marshall et al., Phys. Rev. Lett. 135, 033201 (2025) [2] N. Huntemann et al., Phys. Rev. Lett. 116, 063001 (2016) [3] T. Lindvall et al., Phys. Rev. Lett. 135, 043402 (2025) [4] M. D. Barrett et al., Phys. Rev. A 100, 043418 (2019) [5] C. Marceau et al., Metrologia 62.4, 045001 (2025) [6] T. Lindvall et al., Phys. Rev. Appl. 24, 044082 (2025)
In neutral atom optical clocks, the higher-order atomic polarizability terms lead to the clock transition frequency shift which is motion-state dependent and nonlinear with the optical lattice depth. We propose to use an auxiliary optical lattice to compensate the influence of the E2-M1 differential polarizability or tune the associated coefficient to a favorable value. We show that by applying this method to Sr and Hg optical lattice clocks, the low or even sub-10-19 clock transition frequency uncertainty from the optical lattice becomes feasible. Finally, the proposed scheme is simple for experimental realization and can be implemented and tested in the existing setups.