Polaritonic linewidth asymmetry in the strong and ultrastrong coupling regime
Journal article, 2023

The intriguing properties of polaritons resulting from strong and ultrastrong light–matter coupling have been extensively investigated. However, most research has focused on spectroscopic characteristics of polaritons, such as their eigenfrequencies and Rabi splitting. Here, we study the decay rates of a plasmon–microcavity system in the strong and ultrastrong coupling regimes experimentally and numerically. We use a classical scattering matrix approach, approximating our plasmonic system with an effective Lorentz model, to obtain the decay rates through the imaginary part of the complex quasinormal mode eigenfrequencies. Our classical model automatically includes all the interaction terms necessary to account for ultrastrong coupling without dealing with the rotating-wave approximation and the diamagnetic term. We find an asymmetry in polaritonic decay rates, which deviate from the expected average of the uncoupled system’s decay rates at zero detuning. Although this phenomenon has been previously observed in exciton–polaritons and attributed to their disorder, we observe it even in our homogeneous system. As the coupling strength of the plasmon–microcavity system increases, the asymmetry also increases and can become so significant that the lower (upper) polariton decay rate reduction (increase) goes beyond the uncoupled decay rates, γ − < γ 0,c < γ +. Furthermore, our findings demonstrate that polaritonic linewidth asymmetry is a generic phenomenon that persists even in the case of bulk polaritons.


ultrastrong coupling

strong coupling


Fabry–Pérot microcavity

plasmonic resonance


Adriana Canales Ramos

Chalmers, Physics, Nano and Biophysics

Therese Karmstrand

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

Denis Baranov

Chalmers, Physics, Nano and Biophysics

Tomasz Antosiewicz

Chalmers, Physics, Bionanophotonics

Timur Shegai

Chalmers, Physics, Nano and Biophysics


21928614 (eISSN)

Vol. 12 21 4073-4086

Stark plasmon-exciton koppling för effektiva foton-foton interaktioner

Swedish Research Council (VR) (2017-04545), 2018-01-01 -- 2021-12-31.

Areas of Advance

Nanoscience and Nanotechnology


Basic sciences

Subject Categories

Atom and Molecular Physics and Optics

Condensed Matter Physics


Nanofabrication Laboratory



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