Light–matter interactions with photonic quasiparticles

By Nicholas Rivera, Ido Kaminer. Nature Reviews Physics, 2020

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Interactions between light and matter play an instrumental role in spectroscopy, sensing, quantum information processing and lasers. In most of these applications, light is considered in terms of electromagnetic plane waves propagating at the speed of light in vacuum. As a result, light–matter interactions can usually be treated as very weak and captured at the lowest order in quantum electrodynamics. However, progress in understanding the coupling of photons to material quasiparticles (plasmons, phonons and excitons) brings the need for a generalized view of the photon at the core of every light–matter interaction. In this new picture, the photon can have greatly different polarization and dispersion and be confined to the scale of a few nanometres. Such photonic quasiparticles enable a wealth of otherwise unobservable light–matter interaction phenomena, in interactions with both bound and free electrons. This Review focuses on the theoretical and experimental developments in realizing new light–matter interactions with photonic quasiparticles. Examples include room-temperature strong coupling, ultrafast ‘forbidden’ transitions in atoms and new applications of the Cherenkov effect, as well as breakthroughs in ultrafast electron microscopy and new concepts for compact X-ray sources. The coupling of photons to material quasiparticles such as plasmons, phonons and excitons opens new possibilities in light–matter interactions. This Review presents a generalized view of such quasiparticles and the technique that describes their interactions with matter: macroscopic quantum electrodynamics. Photonic quasiparticles are quantized time-harmonic solutions of Maxwell’s equations in an arbitrary inhomogeneous, dispersive and possibly non-local medium. Surface plasmon–polaritons, phonon–polaritons, exciton–polaritons and all other polaritons are examples of photonic quasiparticles. Moreover, photons in cavities, localized and bulk plasmons, and even acoustic phonons are also special cases of photonic quasiparticles. Certain photonic quasiparticles can confine electromagnetic fields to dimensions much smaller than the wavelength of a photon. Specifically, polaritons in 2D materials, such as graphene and hexagonal boron nitride, allow simultaneously high confinement and low optical losses. Macroscopic quantum electrodynamics prescribes the quantization of the photonic quasiparticles in an arbitrary medium, and can describe the interaction of any photonic quasiparticle with any type of quantum matter (for example, arbitrary emitters) in terms of elementary emission and absorption processes. For bound-electron emitters, the confinement of photonic quasiparticles enables ultrafast spontaneous emission and few-molecule strong coupling, as well as possible new phenomena, such as forbidden transitions and multiphoton spontaneous emission. For free-electron emitters, photonic quasiparticles enable new applications of the Cherenkov effect in particle detectors, as well as new concepts for compact X-ray sources and new applications in ultrafast electron microscopy.

View Paper: https://www.semanticscholar.org/paper/97de91d8df5c8d14223e22cf9762e0686412ad02

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  1. A. Gorlach
  2. Nicholas Rivera
  3. M. Tzur
  4. M. Birk
  5. M. Krüger
  6. Ido Kaminer
  7. Oren Cohen

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