We present a compact high-resolution absolute-gravity gradiometer based on dual ${}^{85}$$\mathrm{Rb}$ atom interferometers using stimulated Raman transitions. A baseline of $L=44.5$ cm and an interrogation time of $T=130$ ms are realized in a sensor head with a volume of only 95 l. Many experimental parameters are optimized to improve the short-term sensitivity, whereas interleaving measurements by reversing the direction of the Raman wave vector are implemented to improve the long-term stability. After an averaging time of 17 000 s, a phase resolution of $104\mu \mathrm{rad}$ is achieved, which corresponds to a gravity-gradient resolution of 0.86 E (1 E = $1\times {10}^{-9}$/${\mathrm{s}}^2$). After the evaluation and correction of systematic errors induced by light shift, the residual Zeeman shift, the Coriolis effect, the self-attraction effect, etc., the instrument serves as an absolute-gravity gradiometer and with it the local gravity gradient is measured to be 3114 (53) E. This instrument combines the merits of high-resolution, high-compactness and high-accuracy, and has good application prospects in many fields.

Ellipse fitting is widely used in the extraction of the differential phase between atom interferometers amid substantial common phase noise. This study meticulously examines the dependency of extraction noise on the differential phase between atom interferometers during ellipse fitting. It reveals that the minimum extraction noise can manifest at distinct differential phases, contingent upon the dominance of different noise types. Moreover, the outcomes are influenced by whether the interferometers undergo simultaneous detection or not. Our theoretical simulations find empirical validation in a compact horizontal atom gravity gradiometer. The adjustment of the differential phase significantly enhances measurement sensitivity, culminating in a differential gravity resolution of 1.6 × 10⁻¹⁰g @ 4800 s.

The coincidence between the atom trajectory and the Raman pulse sequence is very important for an intersection type atom interferometer. Here we present a feedback control technique for the atom trajectories in our horizontal gravity gradiometer, which improves the stabilities of the trajectories by about 2 orders of magnitude. Through the further study of the dependence of the interferometer contrasts on the atom trajectories, we lock the trajectories at optimal positions. And by this technique, the sensitivity of the gravity gradiometer is improved from 982 E/Hz^1/2 to 763 E/Hz^1/2, while the long-term stability is enhanced more significantly and reaches 8.9 E after an integration time of 6000 s. This work may provide hints to other experiments based on intersection type atom interferometers.

Atom interferometer (AI)-based dynamic gravimeters enable high-precision absolute gravity measurements, which are crucial for applications in geophysics, navigation, resource exploration, and metrology. Understanding their underlying mechanisms and minimizing measurement noise is essential for enhancing performance. This work investigates gravity-measurement noise in AI-based systems induced by the dead time of the classical accelerometer. Using actual dynamic gravity-measurement data, we demonstrate that a dead time of 0.12 s introduces significant gravity-measurement noise, reaching 8 mGal. To elucidate the mechanism of this noise, we derive a frequency-domain formula, identifying high-frequency aliasing as its source. Analysis of the derived expressions indicates that reducing the dead-time duration and suppressing the acceleration’s high-frequency noise are effective strategies for mitigating this noise. This work provides significant insights into noise analysis and the future design of AI-based dynamic gravimeters.

The weak equivalence principle (WEP) is a central pillar of general relativity. Its precise test with quantum systems in space offers a unique window onto new physics. Here, we report an in-orbit quantum test of the WEP. A dual-species ( ⁸⁵ Rb/ ⁸⁷ Rb) atom interferometer is realized aboard the China Space Station. Methods of platform motion suppression, fluorescence detection switching, and two-photon detuning switching are developed to eliminate phase noise and improve measurement accuracy. A test uncertainty of 2.8 × 10 ⁻⁸ is obtained from 280 days of WEP test data, and a test result of (−2.7 ± 4.7) × 10 ⁻⁷ is achieved after error estimation. This improves prior atom-interferometric WEP tests in microgravity by three orders of magnitude. This work paves the way for space-borne quantum inertial sensors and their application to future fundamental physics in space.

Differential light shift (DLS) is an important error term that limits the atom interferometer’s measurement precision, especially for the case of the electro-optic modulator (EOM)-based scheme, where multiple laser sidebands exist, and their ratios are hard to control synchronously. This article carried out an experimental and theoretical study on this subject. By conducting long-term gravity measurement, we find that the gravity exhibits drifts of about 13.13 μGal, and is strongly correlated to the Raman laser’s sidebands. A model of the DLS-induced gravity error is established and a DLS compensation method is proposed to suppress the gravity drift to 2.54 μGal. Besides the compensation method, we propose a Dual-Sideband Ratio Locking scheme to more robustly eliminate the gravity measurement drift. By feeding back to both the EOM microwave power and the tapered amplifier’s temperature, this method locks both the ±1 order sideband to a stability level of ${10}^{-5}$, which corresponds to a gravity error of less than 0.1 μGal. Long-term gravity measurement is carried out after the locking method, showing a long-term stability of 1.6 μGal. The proposed methods will benefit the suppression of the DLS effect for high-precision atom interference measurement.