<span class="mw-page-title-main">Polariton</span>
Fabrice P. Laussy's Web

Polariton

A polariton can be seen as a molecule of light and matter. Much like an atom binds an electron to a nucleus, a polariton binds a photon (a particle of light) to a material excitation (a particle of matter), typically an exciton. There are various types of polaritons, depending on what the photon couples to, but the most popular type is the exciton-polariton. This also provides the basic picture which remains valid for most other types of polaritons.

The exciton is unstable, like a positron (it is in fact a bound electron-hole pair), an after a while, recombines to create another photon. The process repeats itself, for as long as the photon stays in the cavity. According to Quantum Mechanics, this generates a quantum superposition of the two possible states, just like the Schrödinger cat, but instead of being alive and dead simultaneously, the particle is light and matter simultaneously:

$$\ket{\mathrm{photon}}+\ket{\mathrm{exciton}}$$

These half-light/half-matter particles have fantastic properties, which they inherit from their underlying components:

  • Polaritons are extremely coherent, like light.
  • Polaritons interact strongly, like matter.

They have a mass, like matter, but a very light-one (the photon has none in vacuum and a small effective one when confined).

Their dynamics consist of characteristic Rabi oscillations.[1] In presence of a weak nonlinearity, this turns into the problem of Josephson oscillations.[2]

The concept was first proposed theoretically, and christened so, by John Hopfield[3], but its most fruitful implementation, in 2D—the cavity-polariton—was discovered experimentally by Claude Weisbuch during a sabbatical stay in Arakawa's group in Tokyo.[4] He referred to it as his «Japanese effect.»[5] Weisbuch did not initially recognized it as a Hopfield polariton, or "bulk polariton", for which the photon is delocalized in the full 3D crystal, but as a cavity QED effect. Weisbuch was in fact already a polariton expert, having reported its first resonant observation 15 years earlier[6]. He didn't mention either surface polaritons or the closely related waveguide polaritons of K. Ogawa et al.[7]

The situation was quickly settled during the July (1993) Erice Summer School on "Confined Electrons and Photons: New Physics and Applications" which featured «heated sessions (involving in particular the two Elis, Eli Burstein and Eli Yablonovitch) on the nature of these excitations» according to Weisbuch himself.[8] The name of "Cavity-Polariton" was then agreed to well describe Hopfield's counterpart in reduced dimensionality, and be more suitable than Weisbuch's initial choice for merely Rabi splitting:

The term "vacuum field Rabi splitting" has so far been used for semiconductor microcavities in analogy to atomic physics where this effect was first observed. From a solid state physics point of view, where dispersion has to be considered, the term "cavity-polariton" is more appropriate.
— R. Houdré, R.P. Stanley and U. Oesterle, 🕮Confined Electrons and Photons: New Physics and Applications. Claude Weisbuch and Elias Burstein (Editors). Springer, 1995. [ISBN: 978-1-4613-5807-7]

The first appearance of the "cavity polariton" term was in Ref. [9], where the idea of the underlying dispersion was being formed. The breakthrough came in Ref. [10] where the now famous polariton dispersion was provided for the first time:

It seems that the theorists who should have predicted cavity-polaritons are C. Andreani et al.,[11] who narrowly missed it by overlooking the dimensionality mismatch could be fixed with a cavity. He seems, however, to have readily understood (and explained) it[12] to R. Houdré et al. as they were shaping the field.[5]

Concepts

Important concepts (I'm particularly interested in) include:

To do

A historical overview of polaritons before the cavity, from Hopfield's lone-warrior paper[3] that gets all the credit despite fairly serious variations with the finally adopted results (including in its operational definition, involving four operators as not taking the rotating wave approximation), along with other contributions.[13][14] The same can be then done from the experimental point of view, especially concerning cavity polaritons and their connections (or missed ones) to surface- and waveguide-polaritons.

Literature

The topic is covered at depth in our book Microcavities. Reviews include [15][16][17][18].

Historical overviews includes Refs. [19][5], etc.

Links

References

  1. ↑ Ultrafast Control and Rabi Oscillations of Polaritons. L. Dominici, D. Colas, S. Donati, J. P. Restrepo Cuartas, M. De Giorgi, D. Ballarini, G. Guirales, J. C. López Carreño, A. Bramati, G. Gigli, E. del Valle, F. P. Laussy and D. Sanvitto in Phys. Rev. Lett. 113:226401 (2014).
  2. ↑ Polaritonic Rabi and Josephson oscillations. A. Rahmani and F.P. Laussy in Sci. Rep. 6:28930 (2016). 
  3. ↑ 3.0 3.1 Theory of the Contribution of Excitons to the Complex Dielectric Constant of Crystals. J. J. Hopfield in Phys. Rev. 112:1555 (1958).
  4. ↑ Observation of the coupled exciton-photon mode splitting in a semiconductor quantum microcavity. C. Weisbuch, M. Nishioka, A. Ishikawa and Y. Arakawa in Phys. Rev. Lett. 69:3314 (1992).
  5. ↑ 5.0 5.1 5.2 Early stages of continuous wave experiments on cavity-polaritons. R. Houdré in Phys. Stat. Sol. B 242:2167 (2005).
  6. ↑ Resonant Polariton Fluorescence in Gallium Arsenide. C. Weisbuch and R. G. Ulbrich in Phys. Rev. Lett. 39:654 (1977).
  7. ↑ Time-of-flight measurement of excitonic polaritons in a GaAs/AlGaAs quantum well. K. Ogawa, T. Katsuyama and H. Nakamura in Appl. Phys. Lett. 53:1077 (1988).
  8. ↑ Microcavities in École Polytechnique Fédérale de Lausanne, École Polytechnique (France) and elsewhere: past, present and future. C. Weisbuch and H. Benisty in Phys. Stat. Sol. B 242:2345 (2005).
  9. ↑ Room-temperature cavity polaritons in a semiconductor microcavity. R. Houdré, R. P. Stanley, U. Oesterle, M. Ilegems and C. Weisbuch in Phys. Rev. B 49:16761 (1994).
  10. ↑ Template:Houdre04a
  11. ↑ Radiative lifetime of free excitons in quantum wells. L. C. Andreani, F. Tassone and F. Bassani in Solid State Commun. 77:641 (1991).
  12. ↑ Optical transitions, excitons and polaritons in bulk and low-dimensional semiconductor structures. L. C. Andreani in 🕮Confined Electrons and Photons: New Physics and Applications. Claude Weisbuch and Elias Burstein (Editors). Springer, 1995. [ISBN: 978-1-4613-5807-7].
  13. ↑ On the interaction between the radiation field and ionic crystals. K. Huang in Proc. R. Soc. Lond. A 208:352 (1951).
  14. ↑ Theory of electromagnetic waves in a crystal in which excitons arise. S. I. Pekar in J. Exp. Th. Phys. [ 33:1022] (1957).
  15. ↑ Polariton–polariton interactions and stimulated scattering in semiconductor microcavities. M. Skolnick, R. Stevenson, A. Tartakovskii, R. Butté, M. Emam-Ismail, D. Whittaker, P. Savvidis, J. Baumberg, A. Lemaı̂tre, V. Astratov and J. Roberts in Mater. Sci. Eng. C 19:407 (2002).
  16. ↑ Polariton panorama. D. N. Basov, A. Asenjo-Garcia, P. J. Schuck, X. Zhu and A. Rubio in Nanophot. 10:549 (2020).
  17. ↑ Microcavity exciton polaritons at room temperature. S. Ghosh, R. Su, J. Zhao, A. Fieramosca, J. Wu, T. Li, Q. Zhang, F. Li, Z. Chen, T. Liew, D. Sanvitto and Q. Xiong in Photonics Insights 1: (2022).
  18. ↑ Coherent phenomena in exciton-polariton systems. F. Toffoletti and E. Collini in J. Phys. Mater. 8:022002 (2025).
  19. ↑ Microcavities in École Polytechnique Fédérale de Lausanne, École Polytechnique (France) and elsewhere: past, present and future. C. Weisbuch and H. Benisty in Phys. Stat. Sol. B 242:2345 (2005).