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Chinese Physics B

Adiabatic Rapid Passage for State Transfer and Sideband Cooling in an 87 Sr Optical Lattice Clock

Jia-An 家安 Li 李, Jin Cao, Chao-Zhe Hu, Wei Tan, Jingjing Xia, Yan-Yan 艳艳 Liu 刘, Chihua Zhou, Hong Chang

Published Sep 15, 2026• 0 citations
Publisher

Abstract

Abstract Effcient population transfer and motional state control are important for optical lattice clocks and precision experiments with lattice-trapped neutral atoms. Here we experimentally investigate adiabatic rapid passage (ARP) on the clock transition of a one-dimensional 87 Sr optical lattice clock and develop a mode-resolved model for ARP on motional sidebands. On the carrier transition, ARP enables robust internal-state transfer with a maximum excitation fraction of 0.98(2). On the blue motional sideband, ARP increases the maximum excitation fraction from 0.47(2) to 0.55(3), and the measured dynamics are consistently reproduced by the mode-resolved model. The model further predicts that the sideband transfer effciency can exceed 0.88 when the carrier Rabi frequency is increased to 15 kHz. Applying ARP to the red-sideband cooling reduces the axial mean vibrational occupation to approximately 0.038, corresponding to a motional ground-state population of 0.96. These results provide a quantitative basis for designing ARP excitation on motional sidebands and for optimizing sideband cooling in lattice-trapped atoms, with direct relevance to coherent state preparation in optical lattice clocks and related precision-measurement experiments in neutral atoms.

DOI
10.1088/1674-1056/aea75d

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In this thesis, I present an experimental study of quantum control techniques for transferring population between vibrational states of atoms trapped in an optical lattice. Results from a range of techniques are compared, including techniques tested previously in the same system. In the study of the Adiabatic Rapid Passage (ARP) technique, control of population transfer is realized through varying the chirp rate and modulation amplitude of a frequency-chirped sinusoidal displacement of the lattice. Meanwhile, dependence of population transfer on the chirp direction is observed, which is explained by a model of ARP in a 3-level system. In the study of the coherent control technique, interference between a one-phonon transition at 2\omega and a two-phonon transition at omega is experimentally demonstrated. The omega and 2\omega transitions are realized by sinusoidally displacing the optical lattice at omega and sinusoidally modulating the lattice depth at 2\omega, respectively. The branching ratio of transitions to the first excited state and to higher excited states is controlled by varying the relative phase between these two pathways. The highest measured branching ratio of 17\pm2 is achieved among all the experiments using this coherent control scheme. In the study of the GRadient Ascent Pulse Engineering (GRAPE) technique, a "pulse" involving both displacement and depth-modulation of the lattice is used to transfer population. This pulse is theoretically engineered with the GRAPE algorithm to optimize the fidelity between the first excited state and the final state, when the lattice Hamiltonian without gravity for a specific lattice depth is considered. The experimental result shows that there is almost no excitation into higher excited states during population transfer from the ground to the first excited state, even when this process is affected by gravity and inhomogeneous broadening in reality. By comparing all the techniques, the GRAPE technique is found to be the best in terms of increasing population transfer into the first excited state while reducing excitation into higher excited states. On the other hand, the ARP technique creates the highest normalized population inversion, a ratio of the difference to the sum of the ground and the first excited state populations.

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Abstract Effcient population transfer and motional state control are important for optical lattice clocks and precision experiments with lattice-trapped neutral atoms. Here we experimentally investigate adiabatic rapid passage (ARP) on the clock transition of a one-dimensional 87 Sr optical lattice clock and develop a mode-resolved model for ARP on motional sidebands. On the carrier transition, ARP enables robust internal-state transfer with a maximum excitation fraction of 0.98(2). On the blue motional sideband, ARP increases the maximum excitation fraction from 0.47(2) to 0.55(3), and the measured dynamics are consistently reproduced by the mode-resolved model. The model further predicts that the sideband transfer effciency can exceed 0.88 when the carrier Rabi frequency is increased to 15 kHz. Applying ARP to the red-sideband cooling reduces the axial mean vibrational occupation to approximately 0.038, corresponding to a motional ground-state population of 0.96. These results provide a quantitative basis for designing ARP excitation on motional sidebands and for optimizing sideband cooling in lattice-trapped atoms, with direct relevance to coherent state preparation in optical lattice clocks and related precision-measurement experiments in neutral atoms.
Sideband cooling is a key technique for improving the performance of optical atomic clocks by preparing cold atoms and single ions into the ground vibrational state. In this work, we demonstrate detailed experimental research on pulsed Raman sideband cooling in a 171Yb optical lattice clock. A sequence comprised of interleaved 578 nm cooling pulses resonant on the 1st-order red sideband and 1388 nm repumping pulses is carried out to transfer atoms into the motional ground state. We successfully decrease the axial temperature of atoms in the lattice from 6.5 μK to less than 0.8 μK in the trap depth of 24 μK, corresponding to an average axial motional quantum number 〈 nz 〉 < 0.03. Rabi oscillation spectroscopy is measured to evaluate the effect of sideband cooling on inhomogeneous excitation. The maximum excitation fraction is increased from 0.8 to 0.86, indicating an enhancement in the quantum coherence of the ensemble. Our work will contribute to improving the instability and uncertainty of Yb lattice clocks.
Efficient high-fidelity ground-state cooling of motional degrees of freedom is crucial for applications in quantum simulation, computing, and metrology. Here, we demonstrate direct ground-state cooling of fermionic Yb 171 and bosonic Yb 174 atoms in two- and three-dimensional magic-wavelength optical lattices on the ultranarrow clock transition. Its high spectral resolution offers the potential for reaching extremely low temperatures. To ensure efficient cooling, we develop a chirped sideband cooling scheme, where we sweep the clock-laser frequency to mitigate the effects of spatial trap inhomogeneities. We further generalize the theoretical description of sideband spectra to higher-dimensional lattices for precise thermometry. We achieve 2D ground-state fractions of 97 % for Yb 171 with an average motional occupation of n ¯ ≃ 0.015 and provide a direct comparison with Yb 174 , reaching similar cooling performance. Applying the same scheme in 3D results in n ¯ ≃ 0.15 limited by layer-to-layer inhomogeneities in the vertical direction. These results demonstrate efficient motional ground-state cooling in optical lattices, especially for bosonic alkaline-earth(-like) atoms, where other methods are not applicable, opening the door to novel protocols for quantum science applications with neutral atoms.
We trap neutral Cs atoms in a two-dimensional optical lattice and cool them close to the zero point of motion by resolved-sideband Raman cooling. Sideband cooling occurs via transitions between the vibrational manifolds associated with a pair of magnetic sublevels, and the required Raman coupling is provided by the lattice potential itself. We obtain mean vibrational excitations ${\overline{n}}_{x}\ensuremath{\approx}{\overline{n}}_{y}<0.024$, corresponding to a population >95>95%>95 in the vibrational ground state. Atoms in the ground state of an optical lattice provide a new system in which to explore quantum state control and subrecoil laser cooling.
Optical lattice clocks require careful preparation of atomic ensembles in order to ensure homogeneous interactions with the clock laser. We demonstrate loading and laser cooling of an ensemble of ytterbium-171 atoms in a 2D optical dipole trap created by an optical cavity. Our loading method ensures that all atoms are located in the intersection of 2 perpendicular dipole traps as verified through absorption imaging. Raman sideband cooling was used to cool the atomic ensemble from 15.7 uK to 6.3 uK as measured through optical sideband spectroscopy on the 578 nm clock transition. Together, these steps improved the transfer of atoms during a Rabi oscillation from the ground to the clock state from approximately 45 percent excitation fraction to 80 percent excitation fraction. The final atomic ensemble preparation is now sufficient for running an atomic clock.
We study quantum control techniques, specifically Adiabatic Rapid Passage (ARP) and Gradient Ascent Pulse Engineering (GRAPE), for transferring atoms trapped in an optical lattice between different vibrational states. We compare them with each other and with previously studied coupling schemes in terms of performance. In our study of ARP, we realize control of the vibrational states by tuning the frequency of a spatial modulation through the inhomogeneously broadened vibrational absorption spectrum. We show that due to the presence of multiple crossings, the population transfer depends on the direction of the frequency sweep, in contrast to traditional ARP. In a second study, we control these states by applying a pulse sequence involving both the displacement of the optical lattice and modulation of the lattice depth. This pulse is engineered via the GRAPE algorithm to maximize the number of atoms transferred from the initial (ground) state to the first excited state. We find that the ARP and the GRAPE techniques are superior to the previously tested techniques at transferring population into the first excited state from the ground state: 38.9±0.2%38.9\pm0.2\%38.9±0.2% and 39±2%39\pm2\%39±2% respectively. GRAPE outperforms ARP in leaving the higher excited states unpopulated (less than 3.3%3.3\%3.3% of the ground state population, at 84%84\%84% confidence level), while 18.7±0.3%18.7\pm0.3\%18.7±0.3% of the ground state population is transferred into higher excited states by using ARP. On the other hand, ARP creates a normalized population inversion of 0.21±0.020.21\pm0.020.21±0.02, which is the highest obtained by any of the control techniques we have investigated.
In this thesis, I present an experimental study of quantum control techniques for transferring population between vibrational states of atoms trapped in an optical lattice. Results from a range of techniques are compared, including techniques tested previously in the same system. In the study of the Adiabatic Rapid Passage (ARP) technique, control of population transfer is realized through varying the chirp rate and modulation amplitude of a frequency-chirped sinusoidal displacement of the lattice. Meanwhile, dependence of population transfer on the chirp direction is observed, which is explained by a model of ARP in a 3-level system. In the study of the coherent control technique, interference between a one-phonon transition at 2\omega and a two-phonon transition at omega is experimentally demonstrated. The omega and 2\omega transitions are realized by sinusoidally displacing the optical lattice at omega and sinusoidally modulating the lattice depth at 2\omega, respectively. The branching ratio of transitions to the first excited state and to higher excited states is controlled by varying the relative phase between these two pathways. The highest measured branching ratio of 17\pm2 is achieved among all the experiments using this coherent control scheme. In the study of the GRadient Ascent Pulse Engineering (GRAPE) technique, a "pulse" involving both displacement and depth-modulation of the lattice is used to transfer population. This pulse is theoretically engineered with the GRAPE algorithm to optimize the fidelity between the first excited state and the final state, when the lattice Hamiltonian without gravity for a specific lattice depth is considered. The experimental result shows that there is almost no excitation into higher excited states during population transfer from the ground to the first excited state, even when this process is affected by gravity and inhomogeneous broadening in reality. By comparing all the techniques, the GRAPE technique is found to be the best in terms of increasing population transfer into the first excited state while reducing excitation into higher excited states. On the other hand, the ARP technique creates the highest normalized population inversion, a ratio of the difference to the sum of the ground and the first excited state populations.