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IEEE Sensors Journal

A Novel Anti-Relaxation Material Applied in Miniaturized Atomic Spin Gyroscope

Shun Li, Longbin Lin, Fangqi Xu, Zhuanfang Bi, Yunong Wu, Haifeng Zhang

Published Apr 21, 2025• 2 citations
Publisher

Abstract

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.

DOI
10.1109/jsen.2025.3561017

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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.
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.
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.
Compared with superconducting quantum interference devices, chip-scale atomic magnetometers using the wafer-level micro alkali vapor cells can be used more conveniently in the applications of geophysical mapping, health care and remote monitoring. Drastic wall collisions and decreased polarization lifetime are the main barriers for the performance of the chip-scale atomic magnetometers. In this study, OTS organic films coated on the inner surface of the micro vapor cells were used to suppress wall collisions and improve polarization lifetime of the alkali atoms in the micro cells. First of all, the fabrication process of wafer-level micro OTS coated vapor cells is introduced, the process is based on anodic bonding technology. Then the prepared wafer-level micro OTS coated vapor cells have been characterized by the water-contact angle test and measured in the micro-machined spin-exchange relaxation free(SERF) atomic magnetometers. Results show that the OTS coating is effective after anodic bonding from the water contact angle test. Results also indicate that the spin exchange relaxation free atomic magnetometer using the micro OTS-coated vapor cell can operate successfully.
We present an experimental investigation of alkali atom vapor cells coated with a high quality anti-relaxation coating material based on alkenes. The prepared cells with single compound alkene based coating showed the longest spin relaxation times which have been measured up to now with room temperature vapor cells. Suggestions are made that chemical binding of a cesium atom and an alkene molecule by attack to the C = C bond plays a crucial role in such improvement of anti-relaxation coating quality.
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.
We present an experimental investigation of alkali atom vapor cells coated with a high quality anti-relaxation coating material based on alkenes. The prepared cells with single compound alkene based coating showed the longest spin relaxation times which have been measured up to now with room temperature vapor cells. Suggestions are made that chemical binding of a cesium atom and an alkene molecule by attack to the C=C bond plays a crucial role in such improvement of anti-relaxation coating quality.