Ultrastrong coupling between light and matter

Annular holes in a thin gold film filled with silicon dioxide enable ultrastrong coupling between light and atomic vibrations. This structure provides opportunities to probe molecules interacting with quantum vacuum fluctuations and develop novel optoelectronic devices. Credit: Oh Group, University of Minnesota

An international team of researchers led by the University of Minnesota Twin Cities has developed a unique process for producing a quantum state that is part light and part matter.

The discovery provides fundamental new insights for more efficiently developing the next generation of quantum-based optical and electronic devices. The research could also have an impact on increasing efficiency of nanoscale chemical reactions.

In this study, the researchers developed a unique process in which they achieved ultrastrong coupling between infrared light (photons) and matter (atomic vibrations) by trapping light in tiny, annular holes in a thin layer of gold. These holes were as small as two nanometers, or approximately 25,000 times smaller than the width of a human hair.

Trapping light can be as simple as making it reflect back and forth between a pair of mirrors, but much stronger interactions can be realized if nanometer-scale metallic structures, or nanocavities, are used to confine the light on ultra-small length scales.

When this happens, the interactions can be strong enough that the quantum-mechanical nature of the light and the vibrations comes into play. Under such conditions, the absorbed energy is transferred back and forth between the light (photons) in the nanocavities and the atomic vibrations (phonons) in the material at a rate fast enough such that the light photon and matter phonon can no longer be distinguished. Under such conditions, these strongly coupled modes result in new quantum-mechanical objects that are part light and part vibration at the same time, known as polaritons.

The stronger the interaction becomes, the stranger the quantum-mechanical effects that can occur. If the interaction becomes strong enough, it may be possible to create photons out of the vacuum, or to make chemical reactions proceed in ways that are otherwise impossible. (ScitechDaily)

The research has been published in Nature Photonics.

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