Quantum gravity gradiometer makes first find outside lab

For the first time, a quantum gravity gradient has been demonstrated outside the lab, an advance that could reduce construction costs and delays, predict volcanic eruptions and uncover hidden natural resources.

quantum gravity gradiometer
(Image: University of Birmingham)

Researchers from the University of Birmingham of the UK National Quantum Technology Hub in Sensors and Timing reported their performance in Nature

The quantum gravity gradiometer, developed on behalf of the Ministry of Defense and in the UKRI-funded Gravity Pioneer project, was used to find a tunnel buried outside one meter below the ground surface.

In use, the quantum gravity sensor measures subtle changes in the pull of gravitational fields when a cloud of atoms falls.

Professor Kai Bongs, head of Cold Atom Physics at the University of Birmingham and principal investigator of the UK’s Quantum Technology Hub Sensors and Timing, explained that atoms are placed in a quantum superposition of traveling simultaneously along two different orbits and that the respective matter wave phases are allowed on intervene in the end.

This creates a phase-dependent imbalance between the number of atoms in one quantum state and the number of atoms in another quantum state.


“The phase difference in this case depends on gravity, so counting the number of atoms in each state at the end provides a way to measure gravity very precisely,” he said via email. “The instrument does this with two atomic clouds at different heights, in order to extract the gravitational gradient.”

He continued: “Eventually we plot the bottom versus the top chamber measurement results in one graph, resulting in an ellipse shape from which we can extract the gravity gradient at the measurement point. This is done for many points to make a map.”

The sensor, developed by Dr. Michael Holynski, head of Atom Interferometry in Birmingham and lead author of the study, overcomes limitations including vibration, instrument tilt and disturbance from magnetic and thermal fields to apply quantum technology in the field.

The successful detection of the tunnel, realized in collaboration with civil engineers led by Professor Nicole Metje from the University’s School of Engineering, is the culmination of a long-term development program that has been closely linked with end users from the start.

“We have now established a start-up called Delta-g. We expect a backpack-sized prototype within the next two years,” said Prof Bongs.

The sensor could one day be deployed in space, said George Tuckwell, director of Geosciences & Engineering and Innovation Lead – RSK Group, which led the study.

“The commercial implications of significantly improved maps of what is below ground level are huge, particularly for the construction industry, which is likely to see reduced costs and delays in construction, rail and road projects,” he said. “The quantum technology, which could eventually be placed on a satellite to map the Earth from space, also provides better prediction of natural phenomena such as volcanic eruptions, and enables underwater and subsurface exploration, including the discovery of natural resources. and archaeological mysteries.”

dr. Holynski added that Birmingham has a prototype with a total weight of 15 kg and would in principle fit on a small satellite.

“There is still work to be done on robustness-to-space,” he said. “There is a significant international effort in cold atoms for space, which has significant implications for fundamental physics, and the UK community is making progress in realizing compact payloads that can be used in future Earth observation applications.

The quantum gravity gradient breakthrough came about in a collaboration between: University of BirminghamRSKDstland Teledyne e2v.

Abhishek Maheswari
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