Scientists slow a tiny sphere to its lowest quantum mechanical state

Researchers at ETH Zürich have announced they have trapped a tiny sphere of glass 100 nanometers in diameter using laser light and slowed its motion to the lowest quantum mechanical state. Scientists have worked in recent years to coax larger and larger objects into behaving quantum mechanically to study them closely. When an object passes through a double slit, it forms an interference pattern characteristic of a wave.

Researchers have achieved this with molecules consisting of a few thousand atoms, but scientists want to be able to observe quantum effects with macroscopic objects. Researchers at ETH Zürich made a step towards that goal in a recent study by coaxing a macroscopic object in the form of a tiny glass sphere into a quantum mechanical state. This sphere contains as many as 10 million atoms.

The team used a tightly focused laser beam which made the sphere hover in an optical trap inside a vacuum container cooled to 269 degrees below zero. Low temperatures are used because the lower the temperature, the smaller the object's thermal motion. Researcher Felix Tebbenjohanns says that to see quantum effects, the nanosphere needs to be slowed all the way to its motional ground state.

The oscillations of the sphere and its motional energy are reduced to the point where quantum mechanical uncertainty relation prevents a further reduction. What that means is as the team freezes the motional energy of the sphere to a minimum, it is close to the quantum mechanical zero-point motion.

To slow the nanosphere, researchers had to be extremely precise and superimpose the light reflected by the sphere onto another laser beam resulting in an interference pattern. From the position of the interference pattern, it's possible to deduce where the sphere is located inside the laser trap. That information was used to calculate how strongly the sphere has to be pushed or pulled to slow it down.

Actual slowing is done by a pair of electrodes with electrical fields that exert precisely determined Coulomb force on the electrically charged nanosphere. Researchers on the project say this is the first time this method has been used to control the quantum state of a macroscopic object in free space.