Abstract Anti-relaxation surface coatings can reduce collisions between alkali-metal atoms and cell walls, thereby prolonging the spin-polarization lifetime of alkali-metal atoms. This phenomenon can considerably improve the performance of quantum sensors. Researchers have focused on the surface topography and composition of anti-relaxation coatings in alkali-metal vapor cells and on methods that provide an increase in the relaxation time of alkali metals. We proposed a novel method to characterise the coating performance of alkali-metal cells by directly measuring the energy dissipation during collisions between the anti-relaxation coating surface and atoms in the cell. We found that the interactions between alkali-metal atoms and the anti-relaxation coating resemble elastic collisions, which can be indirectly characterised by the energy dissipation during interactions between an atomic force microscopy tip and atoms. In addition, we confirmed that the energy dissipation between collisions is positively correlated with the relaxation characteristics of alkali metals at various temperatures. This discovery is of great significance as it can be utilised to characterise the anti-relaxation coating performance of alkali-metal cells by directly analysing the energy dissipation of anti-relaxation coatings instead of measuring the relaxation time.
Abstract Anti-relaxation surface coatings can reduce collisions between alkali-metal atoms and cell walls, thereby prolonging the spin-polarization lifetime of alkali-metal atoms. This phenomenon can considerably improve the performance of quantum sensors. Researchers have focused on the surface topography and composition of anti-relaxation coatings in alkali-metal vapor cells and on methods that provide an increase in the relaxation time of alkali metals. We proposed a novel method to characterise the coating performance of alkali-metal cells by directly measuring the energy dissipation during collisions between the anti-relaxation coating surface and atoms in the cell. We found that the interactions between alkali-metal atoms and the anti-relaxation coating resemble elastic collisions, which can be indirectly characterised by the energy dissipation during interactions between an atomic force microscopy tip and atoms. In addition, we confirmed that the energy dissipation between collisions is positively correlated with the relaxation characteristics of alkali metals at various temperatures. This discovery is of great significance as it can be utilised to characterise the anti-relaxation coating performance of alkali-metal cells by directly analysing the energy dissipation of anti-relaxation coatings instead of measuring the relaxation time.
Abstract Alkali‑metal vapor cells are critical for quantum precision measurement devices such as atomic gyroscopes, magnetometers and clocks. The anti‑relaxation coating on cell walls determines atomic spin polarization lifetime and measurement sensitivity. Conventional evaluations depend on short‑term relaxation tests and fail to characterize long‑term coating stability and microscopic degradation. This work proposes a novel evaluation method based on a cumulative relaxation damage factor. From long‑range kinetic perspectives, alkali‑metal surface dynamics are decomposed into three elementary processes quantified by adsorption energy, charge transfer and diffusion barrier. Drawing on Lusser’s reliability law, we construct this unified factor to interpret relaxation mechanisms and assess coating performance. A first‑principles computational framework with periodic slab models is established for alkali‑metal and organic/inorganic interfaces, validated using experimental interaction parameters of four typical coatings. The simulation results demonstrate that the proposed cumulative relaxation damage factor effectively distinguishes the anti-relaxation performance of different coatings and exhibits general applicability across various alkali-metal species. This study converts cumulative long‑range kinetic relaxation into microscopic coating design rules, offering a theoretical tool for wall‑collision relaxation analysis, coating screening and quantum sensing instruments optimization.
Spin-exchange relaxation-free (SERF) co-magnetometers exhibit broad application prospects in navigation-grade gyroscopes and fundamental physics experiments. However, their performance is constrained by finite spin relaxation times. To address this challenge, long-relaxation-time vapor cells have been realized through the introduction of dry-film anti-relaxation coatings. Such coatings form a stable hydrophobic layer on the inner walls of the vapor cell, which reduces the adsorption energy of alkali-metal atoms and suppresses wall-induced spin-destruction processes, thereby enhancing polarization retention and extending the coherence times of both electronic and nuclear spins. Nevertheless, a clear quantitative relationship between the coating properties and the resulting anti-relaxation performance has not yet been established. To resolve this issue, the present study introduces the background potential field in the Hamiltonian as an intermediate variable, linking the surface adsorption energy of the coating to atomic spin relaxation processes. From the perspective of microscopic energy structure, a theoretical mapping between coating characteristics and anti-relaxation performance is constructed, thereby filling a critical gap in the theoretical understanding of anti-relaxation coating mechanisms.
Anti-relaxation coatings are commonly employed in the alkali metal vapor cells of spin-exchange relaxation-free (SERF) atomic magnetometers, as they can prevent spin depolarization of alkali metal atoms. However, the anti-relaxation mechanism and the interaction process between atoms and coatings remain unclear. This lack of understanding hinders the further improvement of the performance of SERF atomic magnetometers. In this study, we employed first-principles density functional theory to comparatively investigate the microscopic interactions between Rb atoms and SiO2 substrates as well as three commonly used organic coatings. The adsorption energies and valence electron loss of Rb atoms during their adsorption processes on these coated surfaces were systematically calculated. It was found that the Rb atoms exhibited the lowest adsorption energy and the highest charge transfer on the SiO2 surface, with values of –3.55eV and 0.90 |e|, respectively. In contrast, on the 1-nonadecene surface, the adsorption energy reached only –0.13eV, with a charge transfer of merely 0.14 |e|. Similar results were observed for other organic coatings and these findings are highly consistent with previous anti-relaxation performance tests, indicating that alkali metal atoms undergo less energy dissipation and charge transfer on the surface of organic coatings, which can better maintain the electron spin polarization state. A close relationship can be established between adsorption energy, charge transfer and the anti-relaxation performance of coatings, which provides effective guidance for future theoretical research and material selection, thus accelerating the development of SERF magnetometers.
In the process of miniaturizing atomic spin gyroscopes, the relaxation due to the wall collisions of the alkali vapor cell leads to a shorter transverse relaxation time, which increases the key index of the atomic spin gyroscope, the angle random walk, and reduces the gyroscope’s accuracy. This paper theoretically analyzes the thermal stability of the interaction between the new anti-relaxation coating and molecules of the vapor cell, as well as the surface energy of the anti-relaxation coating molecular groups. Based on the results, a new anti-relaxation coating material and its preparation process were proposed. A novel anti-relaxation coating was experimentally prepared. Compositional analysis confirmed its successful covalent bonding with hydroxyl groups on the cell inner-surface, demonstrating superior thermal stability. Through comparative experiments including surface morphology analysis, contact angle measurement, and transverse relaxation time measurement, the new anti-relaxation coating proposed in this paper exhibits lower surface energy. It also has more excellent anti-relaxation performance compared to the traditional OTS anti-relaxation coating.
Paraffin and octadecyltrichlorosilane (OTS) coatings can alleviate collisions between alkali-metal atoms and cell walls and then prolong the atomic spin-polarization lifetime. The surface structure and collision effects of these antirelaxation coatings, as well as the methods to avoid antirelaxation invalidity, have been the focus of researchers. This study investigated the thermolability of coating surface structure and the collision interactions between alkali metal atoms and coatings, considering the influence of various coating preparation factors, where this collision interaction is indirectly analyzed by measuring the collision energy dissipation between an atomic force microscopy (AFM) probe and the atoms on the coating surface. We found that appropriate evaporation time, carbochain length, and postannealing process can enhance the thermostability of the paraffin coating and eliminate its morphological defects. Furthermore, the OTS/water concentration, the soaking time, and the type of solvent have different levels of influence on the cluster formation and the thermostability of the OTS coatings. Moreover, the antirelaxation performance of coatings has been shown to be characterized by counting the energy dissipated when the AFM probe collides with the antirelaxation coating, replacing the conventional light-atom interaction- based method for measuring the relaxation characteristics, but requiring specific coating preparation factors to be maintained.
Many technologies based on cells containing alkali-metal atomic vapor benefit from the use of antirelaxation surface coatings in order to preserve atomic spin polarization. In particular, paraffin has been used for this purpose for several decades and has been demonstrated to allow an atom to experience up to 10 000 collisions with the walls of its container without depolarizing, but the details of its operation remain poorly understood. We apply modern surface and bulk techniques to the study of paraffin coatings in order to characterize the properties that enable the effective preservation of alkali spin polarization. These methods include Fourier transform infrared spectroscopy, differential scanning calorimetry, atomic force microscopy, near-edge x-ray absorption fine structure spectroscopy, and x-ray photoelectron spectroscopy. We also compare the light-induced atomic desorption yields of several different paraffin materials. Experimental results include the determination that crystallinity of the coating material is unnecessary, and the detection of C[Double Bond]C double bonds present within a particular class of effective paraffin coatings. Further study should lead to the development of more robust paraffin antirelaxation coatings, as well as the design and synthesis of new classes of coating materials.