Controlling ultrastrong light-matter coupling at room temperature

Physicists at Chalmers University of Technology in Sweden, together with colleagues in Russia and Poland, have managed to achieve ultrastrong coupling between light and matter at room temperature. The discovery is of importance for fundamental research and might pave the way for advances within, for example, light sources, nanomachinery, and quantum technology.

Chalmers University of Technology team has been well known for its work in light-matter coupling.

The newly presented results offer a glimpse into the domain of the so called ultrastrong coupling, wherein the coupling strength becomes comparable to the resonant frequency of the oscillators. The coupling in this work is realised through interaction between light and electrons in a tiny system consisting of two gold mirrors separated by a small distance and plasmonic gold nanorods. On a surface that is a hundred times smaller than the end of a human hair, the researchers have shown that it is possible to create controllable ultrastrong interaction between light and matter at room temperature and atmospheric pressure.

To understand the system the authors have realised, one can imagine a resonator, in this case represented by two gold mirrors separated by a few hundred nanometers, as a single tone in music. The nanorods fabricated between the mirrors affect how light moves between the mirrors and change their resonance frequency. Instead of just sounding like a single tone, in the coupled system the tone splits into two: a lower pitch, and a higher pitch.

The number of gold nanorods sandwiched between the mirrors controls how strong the interaction is. But at the same time, it controls the so-called zero-point energy of the system. By increasing or decreasing the number of rods, it is possible to supply or remove energy from the ground state of the system and thereby increase or decrease the energy stored in the resonator box.

The results have been published in Nature Communications.

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