Optical clocks have the potential to be 100 times more accurate than current best cesium atomic clocks within a fraction of the averaging time.This corresponds to a fractional uncertainty of the clock frequency on the level of 10 -18 and requires highaccuracy knowledge of systematic frequency shifts, such that they can be avoided or corrected for.In strontium optical lattice clocks an ensemble of ultracold strontium atoms is conned in an optical lattice, to allow for spectroscopy of the reference transition 5s 2 1 S 0 5s5p 3 P 0 in the Lamb-Dicke regime.The by far largest systematic frequency shift of the strontium clock transition is caused by its high sensitivity to blackbody radiation (BBR).The knowledge of the resulting frequency shift limited the achievable clock uncertainty to about 1 × 10 -16 .In this thesis for the rst time an experimental approach was followed, to determine the sensitivity of the strontium clock transition to blackbody radiation.At an environmental temperature of 300 K the resulting frequency shift corresponds to 2.277 8(23) Hz.The achieved uncertainty contributes with 5 × 10 -18 to the fractional systematic uncertainty of the clock frequency.The determination is based on a precision measurement of the dierence of static polarizabilities of the two clock states ∆α dc = α(5s5p 3 P 0 ) -α(5s 2 1 S 0 ) = 4.078 73(11) × 10 -39 Cm 2 /V.For this the dc Stark shift of the clock transition has been measured in the accurately known electric eld of a precision plate capacitor, which has been developed in this work.The attained static polarizability dierence ∆α dc corresponds to the rst term of a power series of the sensitivity to BBR.Higher orders are accumulated as dynamic part of the BBR shift.Which has been modelled using ∆α dc and experimental data for other atomic properties.To interrogate the ultracold atoms in the electric eld a novel transport technique has been developed, which uses the magic wavelength (813 nm) optical lattice to convey the atoms.For this, the interference pattern is translated together with the foci of the far-detuned lattice beams, by simultaneous translation of the lattice optics.In this way ultracold atoms have been transported within 250 ms over 5 cm, or several Rayleigh ranges respectively without signicant atom loss or heating.In the course of this work the rst frequency measurement with the strontium lattice clock of Physikalisch-Technischen Bundesanstalt (PTB) has been performed.The frequency of the 87 Sr clock transition was measured to be 429 228 004 229 872.9(5)Hz.The strontium lattice clock itself contributed with 1.5 × 10 -16 to the overall fractional uncertainty.Furthermore the thermal radiation eld in a cryogenic blackbody environment was modelled and a draft of a corresponding environment of the atoms was designed, which is suitable to be implemented in the strontium lattice clock of PTB.
Optical clocks have the potential to be 100 times more accurate than current best cesium atomic clocks within a fraction of the averaging time.This corresponds to a fractional uncertainty of the clock frequency on the level of 10 -18 and requires highaccuracy knowledge of systematic frequency shifts, such that they can be avoided or corrected for.In strontium optical lattice clocks an ensemble of ultracold strontium atoms is conned in an optical lattice, to allow for spectroscopy of the reference transition 5s 2 1 S 0 5s5p 3 P 0 in the Lamb-Dicke regime.The by far largest systematic frequency shift of the strontium clock transition is caused by its high sensitivity to blackbody radiation (BBR).The knowledge of the resulting frequency shift limited the achievable clock uncertainty to about 1 × 10 -16 .In this thesis for the rst time an experimental approach was followed, to determine the sensitivity of the strontium clock transition to blackbody radiation.At an environmental temperature of 300 K the resulting frequency shift corresponds to 2.277 8(23) Hz.The achieved uncertainty contributes with 5 × 10 -18 to the fractional systematic uncertainty of the clock frequency.The determination is based on a precision measurement of the dierence of static polarizabilities of the two clock states ∆α dc = α(5s5p 3 P 0 ) -α(5s 2 1 S 0 ) = 4.078 73(11) × 10 -39 Cm 2 /V.For this the dc Stark shift of the clock transition has been measured in the accurately known electric eld of a precision plate capacitor, which has been developed in this work.The attained static polarizability dierence ∆α dc corresponds to the rst term of a power series of the sensitivity to BBR.Higher orders are accumulated as dynamic part of the BBR shift.Which has been modelled using ∆α dc and experimental data for other atomic properties.To interrogate the ultracold atoms in the electric eld a novel transport technique has been developed, which uses the magic wavelength (813 nm) optical lattice to convey the atoms.For this, the interference pattern is translated together with the foci of the far-detuned lattice beams, by simultaneous translation of the lattice optics.In this way ultracold atoms have been transported within 250 ms over 5 cm, or several Rayleigh ranges respectively without signicant atom loss or heating.In the course of this work the rst frequency measurement with the strontium lattice clock of Physikalisch-Technischen Bundesanstalt (PTB) has been performed.The frequency of the 87 Sr clock transition was measured to be 429 228 004 229 872.9(5)Hz.The strontium lattice clock itself contributed with 1.5 × 10 -16 to the overall fractional uncertainty.Furthermore the thermal radiation eld in a cryogenic blackbody environment was modelled and a draft of a corresponding environment of the atoms was designed, which is suitable to be implemented in the strontium lattice clock of PTB.
A major obstacle for optical clocks is the frequency shift due to black body radiation. We discuss how one can tackle this problem in an optical lattice clock; in our case 87-Sr: firstly, by a measurement of the dc Stark shift of the clock transition and, secondly, by interrogating the atoms in a cryogenic environment. Both approaches rely on transporting ultracold atoms over several cm within a probe cycle. We evaluate this approach of mechanically moving the optical lattice and conclude that it is feasible to transport the atoms over 50 mm within 300 ms. With this transport a dc Stark shift measurement will allow to reduce the contribution of the blackbody radiation to the fractional uncertainty below 2 * 10^-17 at room temperature by improving the shift coefficient known only from atomic structure calculations up to now. We propose a cryogenic environment at 77 K that will reduce this contribution to few parts in 10^-18.
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)
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.
Accurate time keeping is critical to the function and advancement of many human endeavours. Atomic clocks based on a microwave transition in atomic Cs have served as primary frequency standards to realise the SI second since their formal adoption in 1967. State-of-the-art, laser cooled, Cs fountains now routinely operate with fractional frequency uncertainties below the 10⁻¹⁵ level in laboratories throughout the world. Over the last decade, efforts to build frequency standards based on optical transitions have come to fruition and potential inaccuracies below the 10⁻¹⁷ level have been demonstrated. Such standards point to the future of time keeping and much development is being pursued to realise the potential of these 'next generation' optical clocks. One such approach, on which this work focusses, relies on a 'magic' wavelength optical lattice trap to provide (almost) Doppler- and recoil-free confinement of atoms during clock interrogation. At this 'magic' wavelength, light induced perturbation of the clock states is equal and so cancels precisely. This thesis describes the design and implementation of an optical lattice frequency standard apparatus based on 88Sr held in a 1D optical lattice. A review of the development of atomic frequency metrology is given from a historical viewpoint and the technology and limitations of current methods discussed. To tackle the blackbody radiation shift, which currently presents the greatest limitation to the Sr lattice clock, imposing at the 10⁻¹⁶ level, a scheme to measure the blackbody radiation shift coefficient at the 10⁻¹⁷ level is developed. Techniques to laser cool and trap atomic strontium are described and the implementation detailed. All laser systems required for clock operation are described including the design and implementation of extended-cavity diode lasers for precision spectroscopy. Details relevant to the eventual operation of the apparatus are discussed.
Molecular lattice clocks enable the search for new physics, such as fifth forces or temporal variations of fundamental constants, in a manner complementary to atomic clocks. Blackbody radiation (BBR) is a major contributor to the systematic error budget of conventional atomic clocks and is notoriously difficult to characterize and control. Here, we combine infrared Stark-shift spectroscopy in a molecular lattice clock and modern quantum chemistry methods to characterize the polarizabilities of the Sr_{2} molecule from dc to infrared. Using this description, we determine the static and dynamic blackbody radiation shifts for all possible vibrational clock transitions to the 10^{-16} level. This constitutes an important step toward millihertz-level molecular spectroscopy in Sr_{2} and provides a framework for evaluating BBR shifts in other homonuclear molecules.
Controlling the Stark perturbation from ambient thermal radiation is key to advancing the performance of many atomic frequency standards. This thermal radiation perturbs the atomic energy levels, inducing a Stark shift to the clock frequency conventionally known as the BBR shift. For over four decades, the BBR shift has been a persistent challenge in the pursuit of better atomic clock performance. For room-temperature optical lattice clocks (OLCs) based on Yb and Sr, the BBR shift represents the largest uncanceled systematic frequency shift while typically also constituting the largest source of uncertainty in these state-of-the-art clocks at the ≈ 1 × 10−18 level. In this thesis, I report on the design, assembly and integration of a BBR enclosure, or “shield,” that achieves an unprecedented BBR shift uncertainty of 1.7 × 10−20 by furnishing the interrogated atoms with a near-ideal BBR environment at a cryogenic temperature, while still allowing all the critical quantum control functions required for clock operation. Also, I present a novel lattice loading technique, known as ratchet loading, which enables programmable control over the spatial distribution of ultra-cold atoms confined in an optical lattice. This method allows for the loading of a large number of atoms, effectively reducing quantum projection noise (QPN) while also mitigating frequency shifts caused by atomic interactions. Additionally, ratchet loading facilitates the creation of spatially resolved atomic ensembles along the lattice, making it particularly useful for lattice light shift measurements and potentially advantageous for emerging techniques that probe atomic coherence beyond the local oscillator (LO) coherence time. With the near-elimination of blackbody radiation (BBR) uncertainty and improved clock stability for systematic evaluations, the realization of a mid- to low-10−19 uncertainty Yb optical lattice clock is now more attainable than ever.