A team of scientists from the University of Vienna, Austria, has succeeded in slowing the rotational movement of a tiny object to the limits of quantum mechanics. As can be read in a study published in the scientific journal Nature Physics, Stephan Troyer’s team achieved the quantum mechanical ground state for two rotational degrees of freedom of a nanoparticle.
Light as an ice-cold bondage
For this experiment, the researchers used a dumbbell-shaped structure made of silicon oxide that has a diameter of just 150 nanometers. This particle was kept suspended in optical tweezers by focused laser beams in a high vacuum.
To ensure that the floating particle stops its natural movement, the researchers use light particles within a mirror chamber as energetic “thieves”. Each individual photon that is deflected by the nanoparticle takes with it a tiny quantum of kinetic energy and transports it outwards via the light field.
Fighting the noise
A critical obstacle in such precision experiments is the phase noise of the laser, which usually leads to undesirable heating. The researchers involved from the TU in Vienna, Austria, and the University of Ulm therefore developed a special feedback process for noise suppression.
Thanks to these technical adjustments, the researchers were able to almost completely freeze the physical tremor of the object in two directions at the same time. The nanoparticle now only moves as minimally as the irrefutable natural laws of the quantum world allow.
Precision beyond imagination
The particle is now so immobile in its prison of light that it hardly fluctuates in a measurable way. To put this accuracy into perspective: alignment is more precise than the width of a tiny bacterium relative to a long compass needle.
This means that objects consisting of around 100 million atoms penetrate into an area that was otherwise only reserved for individual atoms or ions. This scalability is an essential aspect for exploring the boundaries between classical physics and quantum mechanics.
New possibilities for sensor technology
In the future, such stabilized nanorotors could function as extremely sensitive detectors for the tiniest of torques. These quantum sensors would be able to measure forces that are orders of magnitude below current capabilities.
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The hurdles of the macroscopic quantum world
Despite this progress, there are hurdles: it currently takes too long for the particle to measurably show its quantum behavior again after a rotation. Given the current size of the object, researchers would have to wait around 50 minutes for an evaluable result, which currently makes work in the laboratory very laborious.
Future experiments would therefore have to be carried out with significantly smaller particles in order to bring these times into a manageable range. Whether the technology can also be transferred to biological materials such as viruses remains a subject of future research.
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