Ultrastrong coupling between nanoparticle plasmons and cavity photons at ambient conditions
Journal article, 2020

Ultrastrong coupling is a distinct regime of electromagnetic interaction that enables a rich variety of intriguing physical phenomena. Traditionally, this regime has been reached by coupling intersubband transitions of multiple quantum wells, superconducting artificial atoms, or two-dimensional electron gases to microcavity resonators. However, employing these platforms requires demanding experimental conditions such as cryogenic temperatures, strong magnetic fields, and high vacuum. Here, we use a plasmonic nanorod array positioned at the antinode of a resonant optical Fabry-Pérot microcavity to reach the ultrastrong coupling (USC) regime at ambient conditions and without the use of magnetic fields. From optical measurements we extract the value of the interaction strength over the transition energy as high as g/ω ~ 0.55, deep in the USC regime, while the nanorod array occupies only ∼4% of the cavity volume. Moreover, by comparing the resonant energies of the coupled and uncoupled systems, we indirectly observe up to ∼10% modification of the ground-state energy, which is a hallmark of USC. Our results suggest that plasmon-microcavity polaritons are a promising platform for room-temperature USC realizations in the optical and infrared ranges, and may lead to the long-sought direct visualization of the vacuum energy modification.


Denis Baranov

Chalmers, Physics, Nano and Biophysics

Battulga Munkhbat

Chalmers, Physics, Bionanophotonics

Elena Zhukova

Moscow Institute of Physics and Technology

Ankit Bisht

Chalmers, Physics, Bionanophotonics

Adriana Canales Ramos

Chalmers, Physics, Nano and Biophysics

Benjamin Rousseaux

Chalmers, Microtechnology and Nanoscience (MC2), Applied Quantum Physics

Göran Johansson

Chalmers, Microtechnology and Nanoscience (MC2), Applied Quantum Physics

Tomasz Antosiewicz

Chalmers, Physics, Bionanophotonics

University of Warsaw

Timur Shegai

Chalmers, Physics, Nano and Biophysics

Nature Communications

2041-1723 (ISSN) 20411723 (eISSN)

Vol. 11 1 2715

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