Entanglement of Polaritons

FWF standalone project, P-22979-N16
Project leader: Gregor Weihs,
National collaboration partners: Gottfried Strasser & Karl Unterrainer, TU Vienna

Quantum Entanglement is a fascinating and little understood phenomenon that gives quantum physics its peculiar features and empowers quantum information processing. It lies at the heart of current quantum technologies like quantum key distribution as well as future applications in quantum repeaters or quantum enhanced measurement. Entanglement research was instrumental in creating the whole field of quantum information and since then the development of new and better sources of entangled photon pairs has sparked many breakthroughs in quantum communication and beyond.

Traditionally, sources of entanglement have been based nonlinear optics in dielectrics. In this project we will exploit a semiconductor effect, the microcavity exciton-polariton (MEP) to facilitate the creation of entanglement. MEPs are half-light half-matter quasiparticles in a microscopic resonator in which light and matter interact very strongly. Due to their ancestry they inherit a peculiar mix of properties, among them a very light effective mass and relatively strong interactions.

It is the strong interactions that we can use to create entanglement by arranging the scattering of MEPs that are created by optical excitation into the desired output channel. In our project, wedesign and create the appropriate semiconductor nanostructures, characterize the properties of the created MEP pairs and test for their entanglement.

MEP entanglement will be useful in a variety of disciplines with one of the most exciting goals being the interaction of entangled photons created from such a source with an MEP Bose-Einstein-Condensate. On the more applied side, MEP based entanglement sources could be developed into electrically pumped, miniaturized devices for the future of quantum communication. These are just two examples of the new and fascinating research directions that such a source of entangled polaritons will be able to unlock.

Parametric scattering is clearly visible as a figure-8 shaped emission pattern (of which the left side is cut off for the most part). We were able to verify enhanced cross- and autocorrelation of the photons emitted in a pair of signal and ider modes. The microcavity for these measurements comes from our collaborator Prof. Wolfgang Langbein (U. Cardiff, UK).

 Parametric polariton scattering


  • L. Einkemmer, Z. Vörös, G. Weihs, and S. Portolan, Polarization entanglement generation in microcavity polariton devices, phys. stat. solid. (b), n/a (2015), DOI: 10.1002/pssb.201451704.
  • Z. Vörös, and G. Weihs, Rayleigh scattering in coupled microcavities: theory, J. Phys. Cond. Mat. 26, 485303 (2014), DOI: 10.1088/0953-8984/26/48/485303.
  • S. Portolan, L. Einkemmer, Z. Vörös, G. Weihs & P. Rabl, Generation of hyper-entangled photon pairs in coupled microcavities, New Journal of Physics 16, 063030 (2014). DOI: 10.1088/1367-2630/16/6/063030
  • P. Mai, B. Pressl, M. Sassermann, Z. Vörös, G. Weihs, et al., Multi-dimensional laser spectroscopy of  exciton polaritons with spatial light modulators, Appl. Phys. Lett. 100, 072109 (2012), DOI: 10.1063/1.3687180.