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arXiv:2604.15417

Ultrastrong Coupling Signatures in Photon Statistics from Terahertz Higgs-Polaritons

Spenser Talkington, Benjamin Kass, Martin Claassen

cond-mat.str-elcond-mat.supr-conphysics.opticsquant-phSubmitted Apr 16, 2026• Announced Apr 17, 2026
v1 · Apr 16, 2026v2 · May 1, 2026v3 · Oct 27, 2026
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Abstract

The ultrastrong coupling regime of cavity photons and quantum materials has emerged as a pathway to modify materials properties, however definitive signatures of ultrastrong coupling remain elusive. Focusing on the quantum photon statistics of light transmitted through a cavity-embedded superconductor, we show that a two-photon Higgs polariton at strong coupling realizes a photonic nonlinearity at the single terahertz photon level. We find that as light-matter coupling increases, the photon statistics show pronounced changes due to the formation of a hybrid photon-matter dark-cavity state with finite photon occupancy, producing testable signatures of ultrastrong coupling. We derive a non-Markovian input output relation and study the cavity-embedded superconductor 2H-NbSe2 as it approaches ultrastrong light-matter coupling. Our results reveal a diagnostic for ultrastrong coupling in the two-photon coincidence statistics that is absent in total counts.

Comments
5+18 pages, 3+11 figures

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