Quantum Plasmonics

Abstract

Quantum plasmonics is an exciting sub-branch of nanoplasmonics where the laws of quantum theory are used to describe light-matter interactions on the nanoscale. Plasmonic materials allow extreme sub-diffraction confinement of (quantum or classical) light to regions so small that the quantization of both light and matter may be necessary for an accurate description. State of the art experiments now allow us to probe these regimes and push existing theories to the limits which opens up the possibilities of exploring the nature of many-body collective oscillations as well as developing new plasmonic devices, that use the particle quality of light and the wave quality of matter, and have a wealth of potential applications in sensing, lasing and quantum computing. This merging of fundamental condensed matter theory with application-rich electromagnetism (and a splash of quantum optics thrown in) gives rise to a fascinating area of modern physics that is still very much in its infancy. In this review we discuss and compare the keys models and experiments used to explore how the quantum nature of electrons impacts plasmonics in the context of quantum size corrections of localised plasmons and quantum tunnelling between nanoparticle dimers. We also look at some of the remarkable experiments that are revealing the quantum nature of surface plasmon polaritons.

Two-fluid hydrodynamic model for semiconductors

“…But when the sizes approach the nanoscale, the model is no longer able to explain experimentally observable phenomena like, for example, the blueshift of the resonance frequency of the localized surface plasmon (LSP) in metallic nanospheres [1]. An improved model that has been successful in describing the optical properties of metals on the nanoscale is the hydrodynamic Drude model (HDM) [2][3][4][5][6][7][8][9][10][11][12]. In this model, the polarization depends nonlocally on the electrical field, and the aforementioned blueshift appears as a size-dependent nonlocal effect [7,13,14].…”

Quantum plasmonic nanoantennas

“…In quantum plasmonics [7,8], one aims to describe how the constituent electrons behave under a perturbation to form a collective mode. This is an important task in modern plasmonics as recent state-of-the-art experiments have explored size regimes, such as extremely small metallic nanoparticles (MNPs) [9] and subnanometer gaps [10][11][12][13], where classical laws, which have been used successfully in the vast majority of plasmonic research done to date, will fail.…”

Nonlinear spectroscopy of plasmonic nanoparticles

“…The polarization P describes the response of matter to an applied external optical field E P = 0 χ E = 0 χ (1) E + χ (2) : E E + χ (3) . .…”