Device could answer basic questions about quantum physics

Measuring the motion of an optically trapped nanoparticle made of billions of atoms.


Scientists at the Optical Society of America have developed a device that measures and control a nanoparticle trapped in a laser beam with unprecedented sensitivity. It holds the potential to help scientists in studying a macroscopic particle’s motion with subatomic resolution.

This is for the first time, scientists used the approach to precisely quantify the motion of an optically trapped nanoparticle made of billions of atoms.

Research team leader Markus Aspelmeyer from the University of Vienna said, “In the long term, this type of device could help us understand nanoscale materials and their interactions with the environment on a fundamental level. This could lead to new ways of tailoring materials by exploiting their nanoscale features.”

“We are working to improve the device to increase our current sensitivity by four orders of magnitude. This would allow us to use the interaction of the cavity with the particle to probe or even control the quantum state of the particle, which is our ultimate goal.”

The new technique utilizes a light-managing nanoscale gadget called a photonic crystal cavity to screen the situation of a nanoparticle suspending in a conventional optical trap. Optical trapping uses an engaged laser bar to apply a force on a question hold it set up.

Aspelmeyer said, “We know that the laws of quantum physics apply on the scale of atoms and the scale of molecules, but we don’t know how large an object can be and still exhibit quantum physics phenomena. By trapping a nanoparticle and coupling it to a photonic crystal cavity, we can isolate an object that is larger than atoms or molecules and studies its quantum behaviors.”

During the experiment, the devices achieve a high level of sensitivity by using a long photonic crystal cavity. Means, when light enters and travels down the nanoscale cavity, some of it leaks out and forms a field called an evanescent field. The evanescent field changes when an object is placed close to the photonic crystal, which in turn changes how the light propagates through the photonic crystal in a measurable way.

The new gadget distinguishes pretty much every photon that communicates with the trapped nanoparticle. This encourages it to accomplish amazingly high sensitivity as well as implies that the new methodology utilizes significantly less optical power contrasted with different strategies in which the vast majority of the photons are lost.

Under vacuum conditions, the researchers demonstrated, for each detected photon, a sensitivity two orders of magnitude higher than conventional methods for measuring nanoparticle displacement in an optical trap. They also report that the strength of the interaction between the particle and evanescent field of the cavity was three orders of magnitude higher than what has been reported previously. Stronger interaction means that the photonic cavity can detect more information about the particle’s movement.

Lorenzo Magrini, first author of the paper said, “This study helped us examine how light in the photonic crystal changes in response to the nanoparticle, we can deduce the position of the nanoparticle over time with very high resolution.”

The study is published in the Optica, the Optical Society’s journal for high impact research.

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