Laser-controlled electron spins shifted the diamond by up to about 1.5 micrometres in vacuum. The team is working to reduce vibrations before more demanding quantum experiments become possible.
Researchers at Japan’s Okinawa Institute of Science and Technology (OIST) moved a 128-milligram diamond using force from its own electron spins. The experiment, led by physicist Jason Twamley, was published in Science Advances and described by Physics World. It demonstrated that changes in a quantum property of electrons could produce measurable movement of a centimetre-scale object.
Twamley said most earlier work in this area focused on levitated nanodiamonds containing a single electron spin. His team instead used a much larger diamond containing billions of defects that trap unpaired electrons.
The defects are called nitrogen-vacancy centres: each consists of a nitrogen atom beside an empty site in the diamond’s carbon lattice. They trap unpaired electrons whose spins—quantum properties linked to magnetic behaviour—are well isolated from the surrounding lattice. That isolation lets the electrons retain a chosen spin state for relatively long periods, even at room temperature.
Pulses from a green, 50-milliwatt laser put the spins into a predefined state. In a magnetic-field gradient, where the field’s strength changes with position, the resulting magnetic changes exerted a force on the diamond. The team measured movements much larger than those seen with the laser switched off.
A carbon rod connected the diamond to a graphite plate held up by magnetic repulsion. The rod passed through magnetic shielding, and the plate carried a mirror. An interferometer, an instrument that measures tiny movements using light, tracked the displacement by reflecting laser light from that mirror.
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| Environment | Displacement |
|---|---|
| Air | Up to about 100 nanometres |
| Vacuum | Up to about 1.5 micrometres |
A nanometre is a billionth of a metre; a micrometre is a millionth of a metre. These are small distances, but the moving object was the whole 128-milligram diamond, not just an individual electron.
The experiment did not place the diamond in a superposition of positions—a quantum state involving two locations at once. Twamley suggested that, under suitable conditions, putting the spins into a superposition could produce a superposition of forces and then of the diamond’s positions. He said achieving those conditions would be extremely tough.
Such experiments could eventually help researchers investigate whether gravity has quantum properties. That remains a possible application, not a demonstrated result or a working gravity sensor. Keeping a massive object in a quantum superposition requires tight control of thermal vibrations and other disturbances that can destroy the state.
Twamley said the team’s low-frequency levitated apparatus was very sensitive to vibration. The researchers are working on vibration isolation to give it a quieter environment—the next practical task on the way towards more demanding quantum experiments.
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