New quantum optics experiment converts laser light to isolated photons

16. October 2020

A new quantum optics experiment might end up being of crucial importance when it comes to safer treatments of information and regarding the research of quantum communication in general. Behind the team of researchers is Professor Anders S. Sørensen, from the DNRF’s Center for Hybrid Quantum Networks (Hy-Q). The experiment has recently been published in the science magazine Nature Photonics.

The image shows light particles during the meeting with atoms while they pass through a glass fiber.
The image shows light particles during the meeting with atoms while they pass through a glass fiber. Photo: Humboldt University.

Physicists around the world have long studied the interaction between light and matter. Quantum optics researchers are particularly interested in exploring how photons are affected when they are sent through a cloud of atoms. An understanding of this interaction can help researchers find safer ways to treat this information.

But to get there, the photons must be sent into the glass fiber in such a way that allows them to get out the other end isolated and in a sorted manner. Researchers from Denmark, Germany, and Austria have now managed to do exactly that with the help of Professor Anders S. Sørensen, from the Center of Excellence Hy-Q, who developed part of the idea behind the experiment and who was part of the theoretical phase of the experiment.

“This is crucial in making quantum technologies where we encode information in individual photons and atoms. If you can do that, you work towards dramatic new ways of processing information. Single photons can, for instance, be used to send encrypted messages which cannot be eavesdropped,” said Sørensen.

A successful experiment

The experiment was about exploring how many of the atoms a photon had to pass through in order to come out isolated at the other end. The researchers had to control the precise number of atoms in the glass fiber to make sure the photons were isolated when they exited the glass fiber. The atoms got caught near an optical nanofiber one hundred times thinner than a human hair.

The atoms were held in place with the help of tweezers of laser light and exactly 0.2 micrometers from the glass fiber’s surface, where the laser light made sure to cool down the atoms to a temperature of a few millionths of a degree above absolute zero.

The researchers’ result showed that 150 atoms had to be trapped near the nanofiber to make sure that the photons would come out one by one. When they used fewer atoms, the photons were unaffected, while more atoms resulted in them coming out in pairs.

The team of researchers found the exact interval that would lead to a transmission of photons and discovered that it could be done with weakly coupled atoms.

“The beauty of this interface is that it’s fairly simple and that it works with weakly coupled atoms, which means it could also be applied to, for example, x-rays in the future,” said Sørensen. He added:

“Such sources have never been available before, so we do not yet understand the full range of applications for them. But potentially, they could be used for ultra-precise sensing and allow for much broader exploration of quantum technologies.

Read the scientific article “Correlating photons using the collective nonlinear response of atoms weakly coupled to an optical mode” here

You can find more information from the University of Copenhagen here.