Earth's gravitational field constantly changes due to shifting mass caused by tectonic activity, water flow, and other dynamic processes. Although these changes are imperceptible in daily life, scientists rely on gravity gradiometers to map subtle variations and link them to features like aquifers or mineral reserves. These maps support everything from resource management to military navigation.
"We could determine the mass of the Himalayas using atoms," said Jason Hyon, chief technologist for Earth Science at JPL and director of the Quantum Space Innovation Center. Hyon is among the scientists behind the Quantum Gravity Gradiometer Pathfinder (QGGPf), outlined in a recent EPJ Quantum Technology paper.
Gravity gradiometers work by comparing the free-fall acceleration of two closely spaced test masses. Any difference in how fast they fall reveals underlying gravitational variations. In the QGGPf system, these test masses are clouds of rubidium atoms cooled to near absolute zero. At such low temperatures, atoms exhibit quantum behavior, behaving like waves. Measuring the difference in how these waves accelerate allows researchers to detect minute gravitational anomalies.
Using atomic clouds as test masses offers long-term measurement stability, noted JPL experimental physicist Sheng-wey Chiow. "With atoms, I can guarantee that every measurement will be the same. We are less sensitive to environmental effects."
This stability, combined with compact design, makes the QGGPf system ideal for space missions. The sensor will occupy just 0.25 cubic meters and weigh about 125 kilograms, significantly smaller than conventional satellite gravity instruments. Quantum-based sensors may also achieve up to 10 times greater sensitivity than traditional systems.
The upcoming technology demonstration, set for launch later this decade, will test key components that manipulate light-matter interactions at atomic scales. "No one has tried to fly one of these instruments yet," said JPL postdoctoral researcher Ben Stray. "We need to fly it so that we can figure out how well it will operate, and that will allow us to not only advance the quantum gravity gradiometer, but also quantum technology in general."
The initiative is a collaborative effort between NASA and commercial partners. JPL is working with AOSense and Infleqtion to develop the sensor head, while NASA Goddard teams with Vector Atomic to refine the laser optical systems.
Beyond Earth science, the QGGPf's success could influence planetary exploration and fundamental physics, expanding our ability to investigate how gravity shapes celestial bodies and the universe at large. "The QGGPf instrument will lead to planetary science applications and fundamental physics applications," Hyon emphasized.
Research Report:Quantum gravity gradiometry for future mass change science
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