A group of researchers from the Delft University of Technology in the Netherlands and the University of Vienna in Austria have created a new light-guiding nanoscale device that can monitor and control a nanoparticle levitating in a traditional optical trap with high sensitivity.
Optical traps (or optical tweezers) are scientific instruments, in which a focused laser beam is used to exert an attractive or repulsive force on a microscopic object to hold it in place.
The amount of force (typically on the orders of piconewtons) depends on the relative refractive index between the particles and surrounding medium. This technique was developed by Arthur Ashkin, an American scientist, who won the 2018 Nobel Prize in Physics at the age of 96 for his invention.
"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 study its quantum behaviors," said Markus Aspelmeyer of the University of Vienna, who led the current research.
Researchers call their new device a photonic crystal cavity, which uses a nanoscale cavity, narrower than the wavelength of the light. When light travels down this cavity, some of it leaks out to form an evanescent field.
An object (such as a nanoparticle) placed near the photonic crystal causes this field to change, which further alters the way light propagates through the photonic crystal. By measuring these changes in the propagation of light, scientists can determine the position of the nanoparticle with very high resolution.
Researchers claim that the photonic crystal cavity can detect almost every photon interacting with the trapped nanoparticle. This enables it to demonstrate extremely high sensitivity and consume much less optical power compared to other techniques.
The team also used their device under vacuum conditions. For each photon detected, the device demonstrated much better sensitivity than the conventional techniques used for measuring nanoparticle displacement in an optical trap. The strength of the interaction between the nanoparticle and cavity's evanescent field was reported to be three orders of magnitude higher than what has been reported previously.
Aspelmeyer hopes their new device can help improve the current understanding about nanomaterials and their interactions with the environment on a fundamental level.
"We are working to improve the device to increase our current sensitivity by four orders of magnitude," Aspelmeyer said.
"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 details of the research have been published in journal Optica.
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