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Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS)

Observation of the Sr clock transition in a Laguerre-Gaussian Lattice Geometry

Miguel A. Cifuentes Marin, Pierre Eberschweiler, Rodolphe Le Targat, Jérôme Lodewyck

Published May 12, 2025• 1 citation
Publisher

Abstract

Improving the performance of optical lattice clocks (OLC) relies on a comprehensive characterization of the effects limiting their accuracy and stability. Intending to reduce the limitation due to cold collisions of trapped atoms below the 10−18level, this paper reports on the progress about the development of a Sr OLC based on a 1D optical lattice with Laguerre-Gaussian (LG) transverse profile in an optical cavity, which allows an average site occupancy of less than one atom per site. We have generated LG0ℓpotentials and realized the trapping of Sr atoms in LG lattices up to ℓ=2, and present the clock spectroscopy of88Sr atoms trapped in these modes, aiming to characterize the residual cold-collisions.

DOI
10.1109/eftf/ifcs64367.2025.11194384

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arXiv:physics/0504080•Physical Review A•Sep 16, 2005•114 citations
Improving the performance of optical lattice clocks (OLC) relies on a comprehensive characterization of the effects limiting their accuracy and stability. Intending to reduce the limitation due to cold collisions of trapped atoms below the 10−18level, this paper reports on the progress about the development of a Sr OLC based on a 1D optical lattice with Laguerre-Gaussian (LG) transverse profile in an optical cavity, which allows an average site occupancy of less than one atom per site. We have generated LG0ℓpotentials and realized the trapping of Sr atoms in LG lattices up to ℓ=2, and present the clock spectroscopy of88Sr atoms trapped in these modes, aiming to characterize the residual cold-collisions.
Aiming to improve the characterization of systematic effects in optical lattice clocks below 10−18, we propose the implementation of Laguerre-Gaussian modes (LGpl) to shape a multi-site trap in the 1D optical lattice of a Sr optical lattice clock, hence reducing the density of atoms, while preserving the advantages of 1D lattices. In this work, we demonstrate the generation of LG0lmodes with l up to 4, and the injection of these modes into an in-vacuum optical cavity intended for the dipole trapping of atoms. Trapping depths up to 200Erfor an LG04were obtained, a priori making it possible to implement LG modes within the clock sequence. We then propose and evaluate two different methods to load atoms in a LG profile.
Optical lattice clocks (OLCs) have achieved an unprecedented relative systematic uncertainty of about 10^{-19}, establishing them as candidates for the upcoming redefinition of the second in the International System of Units. Currently, the accuracy of OLCs is primarily limited by black body radiation (BBR), cold collisions, and lattice light shift effects. Various strategies are being explored to mitigate these limitations, including using cryogenic environments to manage BBR and using new trapping geometries to control atomic distributions and interactions. In this project, we propose a new OLC setup that aims to characterize BBR and density effects below the 10^{-18} level. To achieve this goal, we have developed a copper science chamber that is placed inside a primary vacuum chamber. This configuration minimizes temperature inhomogeneities around the atoms to within a few tens of millikelvin (mK). The system features an adaptable one-dimensional (1D) optical lattice shaped with Laguerre-Gaussian LG_{0ell} modes to increase the number of trapping sites while reducing atomic occupancy per site. We created shaped lattices with values of ell from 0 to 4 whose trap depths were compatible with clock operation. We trapped thousands of atoms in TEM_{00}, LG_{01}and LG{02} shaped lattices and performed low-resolution clock spectroscopy on bosonic ^{88}Sr, yielding 100 Hz-wide transitions. To investigate cold collision effects, we plan to implement a second cooling stage using the ^1text{S}_0 rightarrow ^3text{P}_1 intercombination transition in strontium. This will increase atomic density, enhancing observable collision effects and enabling the detection of motional sidebands. These measurements will provide insight into the anharmonicity of LG-shaped lattices and help validate the lattice light shift model under varying trap conditions. Finally, the clock setup is still under construction. Current work focuses on enclosing the interrogation chamber within the primary vacuum to improve the thermal homogeneity and reduce the uncertainty related to BBR, and at the same time, the instrumentation required for high-resolution spectroscopy is currently being installed.
We report on recent realization of an optical lattice clock operating on the1S0-3P0transition in88Sr, at LENS laboratories. The clock transition is excited with the technique of magnetic field-induced spectroscopy. New experimental techniques has also been developed in order to simplifies the clock spectroscopy in Sr atoms. The first new method helps in the first search of the clock transition without the use of extensive frequency metrology hardware and in particular optical frequency combs. This technique exploits a near coincidence in the atomic wavelengths of the1S0-3P0clock and1S0-3P1second stage cooling transitions in Sr, which are only 5 THz far apart. This coincidence enables the use of an optical (transfer) cavity to reference the frequency of the clock transition relative to that of the much stronger cooling transition. Secondly we reduce the complexity of the experimental setup by using only semiconductor laser sources in the apparatus. With this setup, about 10488Sr atoms are trapped in a 1D lattice formed by 200 mW of radiation tuned near the magic wavelength at 813 nm. We will present a first uncertainty budget for our optical lattice clock based on88Sr with particular attention to density dependent collisions, which led to an unexpectedly high signal contrast for long interaction times. In view of an absolute frequency measurement of clock transition we'll also present recent experimental results on optimization of an home made Ti:Sa optical frequency comb. Additionally, we anticipate that the simplification of the experimental setup presented will help address a wider range of applications including those requiring transportable devices. Along these lines we will report progress on the realization of the first transportable Sr optical lattice clock.
We present experimental results for an optical lattice clock operating on the1S0harr3P0transition in88Sr, which is excited with the technique of magnetic field-induced spectroscopy To reduce the complexity of the setup we have developed a set of new experimental techniques that greatly simplifies the clock spectroscopy in Sr atoms. First, we developed a method for finding the clock transition that removes the need for extensive frequency metrology hardware and optical frequency combs. This technique exploits a near coincidence in the atomic wavelengths of the1S0harr3P0clock and1S0harr3P1second stage cooling transitions in Sr, which are only 5 THz far apart. This coincidence enables the use of an optical (transfer) cavity to reference the frequency of the clock transition relative to that of the much stronger coolign transition Second, all laser sources in the experimental setup are based on semiconductor technology, which greatly reduces the complexity of the apparatus. With this setup, about 10488Sr atoms are trapped in a 1D lattice formed by 200 mW of radiation tuned near the magic wavelength at 813 nm. Preliminar uncertainty budget for our optical lattice clock is also presented, with particular attention to density dependent collisions, which led to an unexpectedly high signal contrast for long interaction times.
We present detailed analyses of our recent experiment on the three-dimensional (3D) optical lattice clock with bosonic 88Sr^{88}\mathrm{Sr}88Sr atoms in which the collisional frequency shift was suppressed by applying a single-occupancy lattice. Frequency shifts in magnetically induced spectroscopy on the 1S0−−3P0{}^{1}{S}_{0}--{}^{3}{P}_{0}1S0​−−3P0​ clock transition ($\ensuremath{\lambda}=698$ nm) of 88Sr^{88}\mathrm{Sr}88Sr were experimentally investigated by referencing a one-dimensional (1D) lattice clock based on spin-polarized 87Sr^{87}\mathrm{Sr}87Sr atoms. We discuss that the clock stability is limited by the current laser stability as well as the experimental sequence of the clock operation, which may be improved to ${\ensuremath{\sigma}}_{y}(\ensuremath{\tau})=2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}/\sqrt{\ensuremath{\tau}}$ by optimizing the cycle time of the clock operation.
We study the trap depth requirement for the realization of an optical clock using atoms confined in a lattice. We show that site-to-site tunneling leads to a residual sensitivity to the atom dynamics hence requiring large depths [(50–100)Er(50\text{--}100){E}_{r}(50–100)Er​ for Sr] to avoid any frequency shift or line broadening of the atomic transition at the ${10}^{\ensuremath{-}17}\text{--}{10}^{\ensuremath{-}18}$ level. Such large depths and the corresponding laser power may, however, lead to difficulties (e.g., higher-order light shifts, two-photon ionization, technical difficulties) and therefore one would like to operate the clock in much shallower traps. To circumvent this problem we propose the use of an accelerated lattice. Acceleration lifts the degeneracy between adjacents potential wells which strongly inhibits tunneling. We show that using the Earth's gravity, much shallower traps (down to 5Er5{E}_{r}5Er​ for Sr) can be used for the same accuracy goal.