Mobile quantum gravity sensor with unprecedented stability (1512.05660v1)

Abstract: Changes of surface gravity on Earth are of great interest in geodesy, earth sciences and natural resource exploration. They are indicative of Earth system's mass redistributions and vertical surface motion, and are usually measured with falling corner-cube- and superconducting gravimeters (FCCG and SCG). Here we report on absolute gravity measurements with a mobile quantum gravimeter based on atom interferometry. The measurements were conducted in Germany and Sweden over periods of several days with simultaneous SCG and FCCG comparisons. They show the best-reported performance of mobile atomic gravimeters to date with an accuracy of $\mathrm{39\,nm/s^2}$ and long-term stability of $\mathrm{0.5\,nm/s^2}$ short-term noise of $96\,\mathrm{nm/s^2/\sqrt{Hz}}$. These measurements highlight the unique properties of atomic sensors. The achieved level of performance in a transportable instrument enables new applications in geodesy and related fields, such as continuous absolute gravity monitoring with a single instrument under rough environmental conditions.

• The paper demonstrates a mobile quantum gravimeter (GAIN) that achieves an accuracy of 39 nm/s² and long-term stability, outperforming traditional static instruments.
• It employs rubidium-87 atom interferometry with a Mach-Zehnder pulse sequence to precisely measure gravitational acceleration in challenging field conditions.
• The breakthrough enables continuous, infrastructure-free geodetic surveys and paves the way for advanced airborne and marine gravity measurements.

Mobile Quantum Gravity Sensor with Unprecedented Stability

The paper discusses remarkable advancements in mobile quantum gravimetry achieved using a gravimeter based on atom interferometry, referred to as GAIN (Gravimetric Atom Interferometer). Conducted by C. Freier et al., this research presents the deployment of a quantum gravimeter for field measurements in Germany and Sweden, demonstrating precision and stability that currently surpass other mobile atomic gravimeters.

Methodology and Experimental Setup

GAIN employs interfering ensembles of rubidium-87 atoms in an atomic fountain configuration, utilizing stimulated Raman transitions. The instrument exploits a Mach-Zehnder interferometer sequence ($\frac{\pi}{2}$-$\pi$-$\frac{\pi}{2}$ pulse sequence) to measure the gravitational acceleration $g$ by analyzing the phase difference of atomic matter waves. It achieves a vertical velocity of 4 m/s and operates with a time $T = 0.26 \, \text{s}$ between pulses. The key innovation is the mobile configuration that allows for precise gravity measurements at different locations, previously limited to static setups.

Numerical Results

The gravimeter achieves an accuracy of 39 nm/s² and displays long-term stability over periods of several days with a vulnerability to short-term noise measured at 96 nm/s²/√Hz. These figures represent a benchmark in mobile gravity measurement precision. The data showed excellent concordance with superconducting gravimeters (SCG) used during comparison measurements, confirming the reliability of the quantum gravimeter under various environmental conditions.

Implications and Applications

This level of accuracy and stability in a transportable instrument opens new avenues for applications in geodesy, such as continuous gravity monitoring and field surveys under challenging environmental circumstances. The reduced sensitivity to micro-seismic noise compared to traditional FCCG (falling corner-cube gravimeters) enhances its usefulness in dynamic settings. Moreover, the capability to maintain precise measurements without relying on infrastructure like massive concrete foundations marks a significant advancement in gravimetry technology.

Theoretical and Practical Contributions

The development of such highly stable and mobile quantum sensors extends the capability of gravity measurement systems beyond traditional limits. The implications for earth sciences include improved monitoring of Earth’s mass redistributions and vertical crustal movements. Practically, the potential for deployment in varied terrains, including remote or unstable environments, positions this technology as a pivotal tool in environmental and geodetic research.

Future Developments

Looking forward, further optimization could potentially reduce noise levels and enhance performance under fluctuating environmental influences. The robustness and portability of atomic gravimeters like GAIN suggest a move towards compact, autonomous gravimeters with broader applications in airborne and marine surveys. This technological evolution is likely to enhance our ability to monitor and understand geophysical processes at unprecedented resolutions and scales.

In conclusion, the advancements detailed in this paper represent a vital step forward in gravimetric sensor technology, showing promise for diverse applications across the fields of geodesy, earth sciences, and beyond. The pioneering fieldwork demonstrates not just a proof of concept but offers a glimpse into the potential future landscape of gravity measurement systems.