Vacuum-dressed superconductivity in NbN observed in a high-$Q$ terahertz cavity

• URL: http://arxiv.org/abs/2601.08191v1
• Date: Tue, 13 Jan 2026 03:42:28 GMT
• Title: Vacuum-dressed superconductivity in NbN observed in a high-$Q$ terahertz cavity
• Authors: Hongjing Xu, Andrey Baydin, Qinyan Yi, I-Te Lu, Ningxu Zhu, T. Elijah Kritzell, Jacques Doumani, Dasom Kim, Fuyang Tay, Angel Rubio, Junichiro Kono,
• Abstract summary: We experimentally observe modified superconductivity in niobium nitride (NbN) thin films within high-quality-factor terahertz cavities.<n>Our analysis reveals significant cavity-induced modifications to the optical conductivity.<n>These results demonstrate a platform for engineering ground states via vacuum--matter coupling.
• Score: 0.0
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Emerging theoretical frameworks suggest that physical properties of matter can be altered within an optical cavity by harnessing quantum vacuum electromagnetic fluctuations, even in the total absence of external driving fields. Among the most intriguing predictions is the potential to noninvasively manipulate superconductivity. Here, we experimentally observe modified superconductivity in niobium nitride (NbN) thin films within high-quality-factor ($Q$) terahertz cavities. Using terahertz time-domain spectroscopy, we characterize the NbN response both in free space and within a high-$Q$ photonic-crystal cavity. Our analysis reveals significant cavity-induced modifications to the optical conductivity. A theoretical model indicates that these changes originate from a substantial ($\sim13\,\%$) reduction in the superfluid density and a minor ($\sim2\,\%$) reduction in the superconducting gap, driven by cavity vacuum fluctuations. These results demonstrate a platform for engineering ground states via vacuum--matter coupling, opening frontiers in cavity materials science.

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