In a laboratory on Okinawa, scientists have for the first time made the quantum spins of electrons move an object a centimetre in size. A diamond suspended above a graphite plate shifted by one hundred nanometres — a distance comparable to a thousandth of a human hair. This is not merely a technical trick: the experiment shows how the forces of the microworld can influence things we are accustomed to regard as classical and subject to gravity.
A team from the Okinawa Institute of Science and Technology used special defects in a diamond crystal — nitrogen-vacancy centres. These defects make it possible to control electron spins with laser light. The graphite plate levitated above a chessboard array of magnets thanks to diamagnetism, while a diamond weighing several milligrams hung below. The total mass of the system is about 128 milligrams.
When the laser pulsed light onto the diamond, the electron spins produced tiny magnetic oscillations. These oscillations turned into a mechanical force that pushed the entire object up and down. The motion was recorded by an interferometer. In air the displacement reached one hundred nanometres, in vacuum up to one and a half micrometres. Importantly, the force arose precisely from a quantum effect, not from heat or vibrations.
Previously, spin forces could be observed only on individual atoms. Now the boundary between the quantum and classical worlds has shifted by eight to nine orders of magnitude in mass. The object is already large enough for gravity to act on it noticeably — this opens the way to testing whether gravity obeys quantum rules.
The experiment was conducted at room temperature, using the long coherence of spins in NV centres. The scientists emphasise: this is a step from the large to the small. Just as diamagnetic levitation lifts maglev trains, here it allowed the system to be isolated from external interference and a pure quantum response to be seen.
In the future, the method could help create macroscopic superpositions — states in which an object is in two places at once. The researchers hope to approach the scale of "Schrödinger's cat" and to build ultra-precise sensors for hunting dark matter or gravitational waves. For now the motion remains classical, but it is caused by a quantum force.
The work has been published in Science Advances. It shows that the boundary between the worlds is not as insurmountable as it seemed, and that every new centimetre brings us closer to understanding the fabric of reality.
