2020/06/30 by Francesco Andreoli, Michael J. Gullans, Alexander A. High +2 · 41 citations
Engineering · Physics and Astronomy · #Atom (system on chip) #Atom optics #Light scattering #Limiting #Near-Field Optical Microscopy #Plasmonic and Surface Plasmon Research #Quantum optics and atomic interactions #Refractive index #Renormalization #Resonance (particle physics) #Scattering #Work (physics) #quant-ph
paper · pdf · doi:10.1103/physrevx.11.011026
published in Physical Review X 11(1) (American Physical Society) · 17 pages, 8 figures
openalex created_date 2020/06/12 · openalex publication_date 2021/02/09 · arxiv created 2021/02/18 · arxiv updated 2021/02/19 · openalex updated_date 2026/08/05
It is interesting to observe that all optical materials with a positive refractive index have a value of index that is of order unity. Surprisingly, though, a deep understanding of the mechanisms that lead to this universal behavior seems to be lacking. Moreover, this observation is difficult to reconcile with the fact that a single isolated atom is known to have a giant optical response, as characterized by a resonant scattering cross section that far exceeds its physical size. Here, we theoretically and numerically investigate the evolution of the optical properties of an ensemble of ideal atoms as a function of density, starting from the dilute gas limit, including the effects of multiple scattering and near-field interactions. Interestingly, despite the giant response of an isolated atom, we find that the maximum index does not indefinitely grow with increasing density but rather reaches a limiting value of n 1.7. This limit arises purely from electrodynamics, as it occurs at densities far below those where chemical processes become important. We propose an explanation based upon strong-disorder renormalization group theory, in which the nearfield interaction combined with random atomic positions results in an inhomogeneous broadening of atomic resonance frequencies. This mechanism ensures that, regardless of the physical atomic density, light at any given frequency only interacts with at most a few near-resonant atoms per cubic wavelength, thus limiting the maximum index attainable. Our work is a promising first step to understand the limits of the refractive index from a bottom-up, atomic physics perspective, and it also introduces the renormalization group as a powerful tool to understand the generally complex problem of multiple scattering of light overall.