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Quantum gravity sensing
The ability to manipulate quantum systems such as neutral atoms brings a huge potential to design extremely precise gravity measurement instruments. Such advanced quantum gravity sensors have transitioned from laboratory research to real-world deployment, where they can detect minute changes in gravity, by collecting data at the atomic level.
Accurate gravity measurements for A range of subsurface mapping applicatIons
Gravity measurements provide valuable information on the mass distribution below the Earth surface, including subsea, relevant to various areas of geoscience and geophysics, from volcanology to civil engineering and geodesy.
The main advantage of quantum gravity sensors over their classical counterparts is their ability to perform continuous absolute measurements, with a high sensitivity and without requiring drift calibration. Indeed, classical gravity sensors rely on a mass on a string, a falling corner cube or a superconducting levitated sphere, to measure mechanical motion under gravity. Quantum gravimeters use laser-cooled atoms in free fall and exploit their wave nature using matter-wave interference (atom interferometry). They precisely measure the phase difference between the two arms of the interferometer, which is directly dependent on the gravitational acceleration.
During the past decades, the need for sensitivity, robustness, compactness, and transportability of instruments measuring the gravitational acceleration has constantly increased. Today, applications typically call for 1 μGal = 10 nm/s² ~10−9 g resolution on time scales ranging from minutes to years. Quantum gravimeters based on matter-wave interferometry with laser cooled atoms address all these challenges at once, even in uncontrolled environments. More than 30 of Exail’s Absolute Quantum Gravimeters (AQG) are currently in operation worldwide. They are deployed for use in real-world applications by geoscientists, demonstrating the technology’s reliability.
ObQG
Exail's Onboard Quantum Gravimeter (ObQG) is a single-axis quantum gravimeter integrating a gyro-stabilized platform
DQG
Exail’s Differential Quantum Gravimeter (DQG) is capable of measuring simultaneously the absolute values of both gravity and its vertical gradient, allowing the detection of smaller masses at shorter ranges.
DQG
Exail’s Differential Quantum Gravimeter (DQG) is capable of measuring simultaneously the absolute values of both gravity and its vertical gradient, allowing the detection of smaller masses at shorter ranges.
DQG
Exail’s Differential Quantum Gravimeter (DQG) is capable of measuring simultaneously the absolute values of both gravity and its vertical gradient, allowing the detection of smaller masses at shorter ranges.
Volcanology
Volcanic activity is driven by underground mass redistribution — including magma accumulation, migration, and withdrawal. Gravimetry directly measures subsurface mass changes, providing unique insight into magma chamber dynamics.
Absolute Quantum Gravimeters enable continuous, high-resolution gravity monitoring under real field conditions. Thanks to their stability and drift-free operation, they deliver reliable long-term measurements critical for tracking volcanic activity, contributing to safer risk management strategies.
First application of quantum technology to volcano monitoring on Mount Etna (2020)
Natural resources management
Absolute quantum gravimeters deliver high-precision data usable for subsurface monitoring, for energy and natural resource applications — including geothermal exploration, mining, oil & gas, and carbon capture and storage (CCS).
By measuring minute variations in the Earth’s gravitational field, they reveal underground density contrasts linked to:
- The structure and extent of geothermal reservoirs (up to ~2 km depth)
- Fault location and structural features
- Depth to basement formations
- Fractured zones, intrusions, and hydrothermal alteration
These gravity anomalies provide actionable insight for exploration and structural mapping.
Photo. P. Dykowski. AQG-B07 from Institute of Geodesy and Cartography, Poland. Measurements taken in the framework of the EQUIP-G project, Terrestrial Use Case: Climate Monitoring (TUC6), supported by the Danish Climate Data Agency.
Hydrology – Monitoring Water Resources and Climate Impact
Understanding water dynamics is essential for geodetic survey and to assess the impact of climate change. By directly measuring tiny variations in the Earth’s gravitational field, Quantum Gravimeters detect subsurface mass changes linked to water movement.
Quantum gravimeters enable precise monitoring of groundwater level variations, aquifer recharge and depletion, glacier mass balance, surface water redistribution as well as long-term hydrological trends. Portable and drift-free, they provide absolute gravity measurements anywhere — from remote field campaigns to permanent monitoring stations. Their atomic reference ensures stable, repeatable performance without mechanical recalibration, making them ideally suited for long-term environmental observation.
Near surface detection – from civil engineering to mining
Exail’s Differential Quantum Gravimeter (DQG) is a new generation of gravity sensor capable of measuring simultaneously the absolute values of both gravity and its vertical gradient (it combines a quantum gravimeter and a quantum gradiometer).
Measuring the gravity gradient allows the detection of small masses at short ranges, which are signatures of underground objects such as water pipes, mines, cavities or high-density structures.
The field version of Exail's DQG was developed within the FIQUgS European project. Installed on a rover, it is dedicated to autonomous and mobile underground mapping, for large-scale surveys in archeology, civil engineering and underground resource management.
Exail's DQG mounted on a rover probed downtown Reims to uncover its medieval past within the FIQUgS European project (Spring 2026).
Photo P. Dykowski. Quantum absolute gravimeters being compared and tested. Hanover, Germany. 2024. ⟨hal-04428550⟩
Metrology and geodesy
Absolute quantum gravimeters based on laser-cooled atoms provide a highly stable and drift-free reference for national metrology institutes and research laboratories. They are among the essential tools for validating the repeatability, accuracy, and long-term stability of gravimeters based on other types of technologies.
By combining atomic stability with field deployability, Exail’s quantum gravimeters support the advancement of high-precision geodesy, fundamental metrology, and global gravity reference networks.
Onboard gravimetry
Onboard quantum gravimetry enables high-spatial resolution gravity mapping from moving platforms such as aircraft and marine vessels. By covering large or hard-to-access areas more efficiently, it can support geophysical surveys and volcano monitoring, while creating new synergies between airborne measurements and terrestrial gravity networks.
In the frame of the EQUIP-G project, Exail and the consortium develop the first commercial onboard quantum gravimeter (ObQG), a single-axis quantum gravimeter integrating a gyro-stabilized platform. Scheduled for delivery by the end of 2027, the instrument targets an accuracy below 0.5 mGal in dynamic conditions. Airborne trials aboard SAFIRE’s ATR42 aircraft and Zeppelin NT airship are planned for 2028 in Italy and Germany to validate its performance and assess its benefits compared with conventional gravimeters.
Preliminary 3D design of the ObQG featuring a sensor head mounted on a gyro-stabilized platform / Photo © Exail
Learn more about CARIOQA-PMP
Towards space quantum gravimetry
Gravity measurement from space allow to ‘look’ beneath Earth’s surface from space. They enable to monitor the evolution of the oceanic currents and atmospheric events, the fresh water cycle, and even study the underground changes tied to seismology and vulcanology. They are also the primary means of performing geodesy by mapping the Earth’s gravity field at global scale, with numerous applications such as improving GNSS accuracy.
Exail has been actively involved in the CARIOQA (Cold Atom Rubidium Interferometer in Orbit for Quantum Accelerometry) project, led by the French and German space agencies (CNES and DLR), and supported by the European Commission. The project aims at deploying a quantum gravity sensor demonstrator in space by 2033, relying on the spatialization of Exail’s atom cooling laser system. This will prepare for a future full scale Earth observation mission.
In 2026, Exail delivered the engineering model of its ultracompact, space-grade laser source to CNES. Commissioning and performance validation of the laser source were successfully completed, with no anomalies detected.
EQUIP-G
European Quantum Infrastructure Project for Gravimetry
Quantum gravimeters are poised to play a key role in a near future to monitor the Earth and tackle some of the most pressing societal challenges. The European project stated in June 2025, involving 20 partners from 11 countries, with expertise in geophysics, metrology, data management and quantum sensors. EQUIP-G plan to establish a European perennial research infrastructure managing a shared park of quantum sensors, and a terrestrial reference gravity network, for the benefit and the sovereignty of Europe.
The first EQUIP-G community workshop was held in June 2026 in Postdam (Germany), with posters and presentations spanning the entire scope of finished, ongoing and planned use cases in hydrology, volcanology, climatology, geodesy, geothermal energy, up to airborne gravity mapping proof of concept. Learn more:
EQUIP-G has received funding from the European Commission's Horizon Europe program, under the HORIZON-CL4-2024-DIGITAL-EMERGING-02 call.
