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Chinese Physics B

Evaluation of the Dynamic Magnetic Field Induced Effects on the Lattice Loading Efficiency of a Spaceborne Sr Optical Lattice Clock

Jiajun Jing, Yong Shen, Xiaokang Tang, Shaolong Zuo, Yongzhuang Zhou, 邓志姣, Hong Chang, 邹宏新

Published Aug 25, 2026• 0 citations
Publisher

Abstract

Abstract We evaluate the effects of the dynamic magnetic field on the lattice-loading efficiency of a spaceborne Sr optical lattice clock. The orbital magnetic field is calculated using the International Geomagnetic Reference Field-14 model and calibrated with in situ MAG-13 magnetometer data to include quasi-static stray fields from onboard electrical equipment. An ensemble Monte Carlo simulation is then employed to systematically investigate the dependencies of the final ensemble-averaged atomic temperature and the optical lattice loading efficiency on the laser saturation parameter $s$ and detuning $\delta$. Feedforward Helmholtz coil compensation based on the IGRF-14 calibrated field prediction restores the time-averaged efficiency from $\bar{\eta} = 5.67\%$ in the uncompensated case to $\bar{\eta} = 13.05\%$. These results quantify the influence of dynamic magnetic fields on lattice loading and provide guidance for magnetic-field compensation in future spaceborne Sr optical lattice clock missions.

DOI
10.1088/1674-1056/ae9e1b

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Abstract We evaluate the effects of the dynamic magnetic field on the lattice-loading efficiency of a spaceborne Sr optical lattice clock. The orbital magnetic field is calculated using the International Geomagnetic Reference Field-14 model and calibrated with in situ MAG-13 magnetometer data to include quasi-static stray fields from onboard electrical equipment. An ensemble Monte Carlo simulation is then employed to systematically investigate the dependencies of the final ensemble-averaged atomic temperature and the optical lattice loading efficiency on the laser saturation parameter sss and detuning δ\deltaδ. Feedforward Helmholtz coil compensation based on the IGRF-14 calibrated field prediction restores the time-averaged efficiency from ηˉ=5.67%\bar{\eta} = 5.67\%ηˉ​=5.67% in the uncompensated case to ηˉ=13.05%\bar{\eta} = 13.05\%ηˉ​=13.05%. These results quantify the influence of dynamic magnetic fields on lattice loading and provide guidance for magnetic-field compensation in future spaceborne Sr optical lattice clock missions.
The microgravity environment modifies the resonance condition that is formed with the participation of gravity in the 689 nm narrow-line magneto-optical trap (red MOT) of a ground-based strontium optical clock. Consequently, a cooling scheme optimized under standard 1g ground-commissioning conditions cannot be directly transferred to an in-orbit space optical clock. In this work, we establish a one-dimensional semiclassical Monte Carlo stochastic dynamics model along the ground-gravity direction to study the cooling dynamics, spatial distribution, and position compensation of a 88Sr narrow-line MOT under microgravity. The simulations show that directly applying ground-optimized parameters in microgravity leads to heating, cloud broadening, and displacement from the lattice position calibrated on the ground. Reducing the detuning can produce a smaller spatial distribution, but this behavior is mainly phase-space truncation and cannot maintain a sufficient effective atom number. We propose a dynamic-control scheme in which the laser detuning and intensity are continuously ramped, achieving an atomic temperature below 3 μK under microgravity while retaining more than 98% of the atoms in the MOT, outperforming the 1g ground-gravity reference case. On this basis, magnetic-gradient screening is used to obtain a cloud size matched to the optical-lattice mode. After an additional compensation magnetic field is introduced, the deviation between the narrow-line MOT center and the lattice position is ∼2.4 μm, far smaller than the transverse scale of the lattice beam. These results provide a physical picture and theoretical guidance for in-orbit commissioning of the narrow-line MOT in a strontium optical clock on the Chinese Space Station.
Abstract An optimized design of a permanent Zeeman slower for an ytterbium optical lattice clock is presented. The dependences of the magnetic field distributions on the detuning and intensity of the cooling laser are studied. The length and corresponding magnetic field distribution of the slower are analyzed by varying the efficiency parameter and saturation parameter of the cooling laser. Considering the slowing efficiency and the loading rate of the magneto-optical trap, the optimum length of the slower is about 15 cm, and its width is about 10 cm in our case. Finally, an adjustable slower with a slowing efficiency of 15.5% is proposed.
Owing to the different requirements to the magnetic field of magnetic-optical trap for the two different stages of cooling of Sr optical lattice clock,the magnetic field conversion needs to be controlled with a certain sequence within a short time for reducing the fleeing of the atoms in the magnetic field conversion.The theory of the anti-Helmholtz coil is discussed,a design of the magnetic field for the two-stage-cooling of Sr optical lattice clock is presented,and an occurring and controlling device for the magnetic conversion,which mainly contains control circuit and protection circuit,is manufactured.The measurement shows that the current through the coil is controlled by the input signal,meeting the experimental requirements.
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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.
Optics lattice clock is a hot topic in the researches of frequency standard and metrology. Neutral mercury atom is one of the most promising candidates for optical lattice clock. Due to its large atomic number, mercury atom is insensitive to black body radiation, which is the severe limitation for developing the optical lattice clocks. To realize the optical lattice clock of neutral mercury atoms, the first step is to implement laser-cooling and trapping of neutral mercury atoms. The cooling transition of mercury atom is 1S0-3P1 transition. The wavelength is 253.7 nm, the line width is 1.27 MHz, and the saturation intensity is 10.2 mW/cm2. Quantum projection noise (QPN) is an important parameter that affects optical lattice clock. Increasing the loading rate of magneto-optical trap (MOT) can help lower the QPN, thereby improving the performance of optical lattice clock. In this work, we calculate the scattering force of deep UV cooling laser, which is exerted on mercury atom in our single chamber MOT, and numerically simulate the one-dimensional motion of the atom in the MOT. It gives us the capture velocity under optimized parameters of the MOT. Then we calculate the loading rate of three-dimensional MOT by a high efficient random sampling method. According to the rate equation of MOT, the loading rate is proportional to the atom number of the steady state, which is the accessible parameter in the experiment. An experimental setup of MOT is established with a high vacuum system and a frequency quadrupled semiconductor laser system. The fluorescence imaging on an EMCCD gives the atom number in the MOT. We also calibrate the vapor density of background mercury gas in the vacuum, and measure the atom number in a steady MOT. We numerically simulate and experimentally study the influences on the atom number on the parameters of MOT, such as laser intensity, laser detuning and magnetic field gradient. The calculated results are in consistent with the experimental results. We also find the optimized parameters to maximize the loading rate. The numerical simulation also gives some results beyond current experimental condition, especially for laser intensity. From the simulations we obtain the optimized MOT parameter and relation for laser cooling of neutral mercury atom. Especially, current deep UV cooling laser with 20 mW of power does not have enough power to enhance the loading rate. These results are rather valuable for designing the next generation of optical lattice clocks for neutral mercury atoms.