A Glass Nanosphere Becomes First Macroscopic Object Under Quantum Standstill In Free Space

The glass nanosphere appearing in green levitating in the center of the optical trap. Image Credit: ETH Zurich

Scientists at ETH Zurich were able to levitate a glass nanosphere using laser light and slow down its motion to its lowest quantum mechanical state. This breakthrough could help us better understand quantum mechanics by bringing it closer to our size as well as employing it in even more technologies.  

The breakthrough, reported in Nature, was only possible thanks to some truly fantastic tech. The sphere, which is 100 nanometers in diameter, was made to levitate in an optical trap. A laser is keeping it suspended in mid-air. The trap is in a vacuum container, and it is cooled down to a temperature just a few degrees above absolute zero.

Even with all of that, the sphere is still not in a quantum state because it’s got too much energy. To slow it down even more, the team uses another laser and the light reflected by the sphere. This creates an interference pattern and the team can tweak the laser in a way that the light pushing and pulling on the sphere makes it slow down into its ground state.

"This is the first time that such a method has been used to control the quantum state of a macroscopic object in free space," senior author and Professor of Photonics, Lukas Novotny said in a statement.

Similar approaches have been achieved in optical resonators but this approach allows for the examining of the sphere in complete isolation once the interference laser is switched off. This allows for the quantum wave of the sphere to expand freely. Something super exciting. Just like electrons and photons are both waves and particles so is this nanosphere. It could be possible one day to test it using the double-slit experiments and see the expected interference pattern.

"For now, however, that's just a pipe dream," Novotny cautioned.

The applications of such an approach could be revolutionary. Just last month, researchers announced they were able to bring the 10-kilogram (22-pound) optomechanical oscillator formed by the mirrors in the LIGO gravitational wave observatory close to its quantum ground state. Reaching this level of “stillness” in larger and larger objects is crucial for making better and better sensors.

There are quantum sensors that are already used to measure the tiniest accelerations or rotations by using interfering atomic waves. The bigger the interfering object the more sensitive the sensor gets. So having nanosphere or larger objects could be a groundbreaking achievement for ultra-precise measurements.  


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