A collaboration led by the Abdus Salam International Centre for Theoretical Physics (ICTP), with key contributions from the SISSA, has developed the first theoretical model of the fractional quantum Hall effect in a cavity. The findings, published in Physical Review X, lay the groundwork for future experiments and offer new insight into light-matter interactions in quantum materials.
The fractional quantum Hall effect, a phenomenon where electron systems exhibit quantized conductivity under extreme conditions, has been extensively studied in free space. Researchers are now exploring what happens when these systems are confined in optical cavities, where light and matter interact strongly.
The new model, developed by theorists from ICTP, SISSA, the Italian National Research Council, the University of Trento, and the Indian Institute of Technology in Chennai, predicts the emergence of “graviton-polaritons”: hybrid particles arising from interactions between photons and a specific type of quasiparticle known as a graviton.
“Our model shows that the photons in the cavity interact in particular with an elusive type of quasiparticle — an emergent particle that captures the collective behaviour of strongly interacting electrons — which, in analogy with gravitational waves, has been called graviton. This interaction gives rise to hybrid light-matter correlated states, the graviton-polaritons,” says Zeno Bacciconi, the study’s first author and a PhD student at SISSA under the supervision of ICTP’s Marcello Dalmonte, a co-author of the paper.
“This new framework gives us a clearer understanding of how quantum Hall systems behave in the presence of a cavity. By predicting precise signatures of graviton-polaritons that should emerge from spectroscopy measurements, it also offers a way to search for these hybrid states in future experiments,” Dalmonte says.
The study also clarifies previous contrasting experimental findings, which in some cases suggested a breakdown of conductivity quantization when quantum Hall materials were confined in cavities. “Our model clearly shows that the cavity does not disrupt the fundamental character of the system,” says Bacciconi. “Further studies are needed to bridge the remaining gap between our theoretical predictions and experimental observations.”
This work represents a significant step in the rapidly evolving field of cavity-embedded quantum materials. As physicists continue to explore new strategies for manipulating quantum matter, the results of this study will serve as a key reference for both theoretical and experimental advances.