Short answer: Atom interferometers use matter waves to measure gravity very precisely, and recent work has pushed them in two directions: portable instruments for field use and lattice-held atoms that allow much longer measurement times. A 2018 Scientific Reports paper describes a transportable quantum gravimeter with long-term stability below 10 nm per second squared, a 2020 Science paper reports holding atoms for 20 seconds in a cavity lattice, and a 2024 Nature paper uses a lattice interferometer to measure the pull of a small source mass. These are laboratory and field-test results from the authors.
2018: a transportable gravimeter
The Scientific Reports abstract says quantum gravimeters based on atom interferometry have shown top-level sensitivity, long-term stability and accuracy, but have remained confined to laboratories because they are complex to operate and sensitive to the environment. The authors report a transportable quantum gravimeter that can be operated under real-world conditions by non-specialists and measures absolute gravitational acceleration continuously with a long-term stability below 10 nm per second squared, which they equate to 1 microGal. They say it features technological innovations that keep the instrument light and small enough for field measurements, and that they characterized it in detail and evaluated its stability in a month-long measurement campaign.
2020: holding atoms instead of dropping them
The Science abstract says atom interferometer performance has been limited by the interrogation time of freely falling atoms. By suspending the separated atomic wave packets in a lattice formed by the mode of an optical cavity, the authors realize an interrogation time of 20 seconds. They say this lets gravitational potentials be measured by holding atoms, and that after seconds of hold time, differences in gravitational potential energy from as little as micrometres of vertical separation produce megaradians of interferometer phase. They report the trapped geometry suppresses vibration-induced phase variance by three to four orders of magnitude, overcoming the dominant noise source in atom-interferometric gravimeters.
2024: a source-mass measurement
The Nature paper notes that free-fall interferometers have measurement times of a few seconds, and that lattice interferometers holding atoms for 70 seconds have been demonstrated but not yet used for precision tests of gravity, because the lattice must balance Earth's gravity with forces a billionfold stronger than the signals and tiny imperfections could cause complex systematic effects. The authors optimize the gravitational sensitivity and use signal inversions to suppress and quantify systematic effects. They measure the attraction of a miniature source mass at 33.3 plus or minus 5.6 (statistical) plus or minus 2.7 (systematic) nm per second squared, consistent with Newtonian gravity, which they say rules out screened fifth-force theories over their natural parameter space. They report an overall accuracy of 6.2 nm per second squared, more than a factor of four better than the best similar measurements with atoms in free fall. They suggest improved cooling and tilt-noise suppression could further raise sensitivity, a future possibility.
Limits
These are different instruments with different goals, so their numbers are not directly comparable. The fifth-force statement applies to the screened theories in the authors' parameter space and is their interpretation. Field operation was shown for one portable instrument over a month-long campaign.
FAQ
What is an atom interferometer gravimeter?
An instrument that uses interfering matter waves of atoms to measure gravitational acceleration, per the 2018 and 2020 abstracts.
How stable was the portable gravimeter?
Long-term stability below 10 nm per second squared, or 1 microGal, in the 2018 paper.
Why hold atoms in a lattice?
Free fall limits interrogation time, and the 2020 authors report 20 seconds when holding atoms in a cavity lattice, with strongly reduced vibration noise.
What did the 2024 experiment test?
The attraction of a small source mass, found consistent with Newtonian gravity, with the authors saying it rules out screened fifth-force theories over their natural parameter space.
Are these in routine use?
The 2018 paper describes a field-ready instrument tested for a month. The others are laboratory experiments.
All field notes