For particle physicists, studying the interactions between photons and electrons has long been an area of interest. After all, observing such phenomena could eventually lead us to the creation of a viable quantum computer.

Physicist Junichiro Kono and his colleagues at Rice University are making headway on a method to create a new condensed matter state, where electrons in a material "couple" after they are manipulated with light and a magnetic field.

For their work, which was described in Nature Physics, the team made use of a custom-built, finely-tuned cavity for terahertz radiation. The result? The researchers detected one of the strongest light-matter coupling phenomena ever observed.


Xinwei Li. Credit: Jeff Fitlow/Rice University

The condensed matter state that the researchers worked on is similar to what's known as Bose-Einstein condensates. Named after physicists Satyendra Nath Bose and Albert Einstein, a Bose-Einstein condensate is essentially a state of matter of a dilute gas of bosons cooled to close to absolute zero.

A previous work was able to prompt atoms to form a gas at ultra-cold temperatures at which all atoms lose their individual identities and behave as a single unit. This time, Kono's team wanted the electrons to be strongly coupled, or "dressed," with light.

The team designed and constructed a high-quality cavity containing an ultra-thin layer of gallium arsenide—the same one that's used to study superfluorescence. Then, the physicists tuned the material with a magnetic field to resonate with a certain state of light inside the cavity, resulting in the formation of polaritons.

“This is a nonlinear optical study of a two-dimensional electronic material,” said Qi Zhang, a former graduate student in Kono's group and lead author of the paper. “When you use light to probe a material’s electronic structure, you’re usually looking for light absorption or reflection or scattering to see what’s happening in the material. That light is just a weak probe and the process is called linear optics."

The team's work could pave the way for the advancement of applications that involve quantum information like quantum computers.

“The light-matter interface is important because that’s where so-called light-matter entanglement occurs. That way, the quantum information of matter can be transferred to light and light can be sent somewhere," Kono said.

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