A team led by Ron Folman at Ben-Gurion University has built the Quantum Galileo Interferometer, or QGI, to compare a freely falling atom's wave phase with one held still.
Ars Technica reported that the device puts a single atom into two trajectories, one launched upward to fall ballistically, the other kept motionless, before recombining them to measure their relative phase.
"Every particle, doesn't matter if it's a car or a spaceship or an atom, is a wave," Folman said.
A tiny experiment with enormous precision
The chip-scale apparatus uses microwave and magnetic pulses on a Bose-Einstein condensate, a state of matter formed when atoms are cooled to extremely low temperatures, made up of about 20,000 rubidium atoms held roughly 113 micrometres below a patterned wire chip.
Magnetic pulses act first as a cannon and then as a parachute, so that one branch of the atom cloud free-falls while the other remains magnetically held in place.
The two trajectories are separated by about 7.5 micrometres, with the longest flight lasting just two-thousandths of a second.
Why this test matters
The experiment addresses a prediction nearly a century old, serving as a direct test of the equivalence principle, the idea underpinning general relativity that gravitational and inertial mass behave identically, applied here in the quantum domain.
The test probes whether standard gravity applies unchanged to matter waves, rather than only to the classical objects general relativity was originally built to describe.
Where the research stands
The result is reported in a paper appearing in Science Advances, giving experimental footing to long-standing theoretical questions at the interface of quantum mechanics and general relativity.
Whether gravity ultimately treats a wave of matter exactly as it treats a falling apple, or whether subtle quantum effects introduce some deviation, remains an open question that experiments like this one are only beginning to probe with the necessary precision.
