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Department of Physics

Polariton BEC

Semiconductor microcavities provide an excellent playground for studying condensation in a dissipative environment. Strong interactions between confined photons and quantum-well excitons lead to new quasi particles called microcavity polaritons which can be studied via far- and near-field techniques, and their interaction properties manipulated externally by changing both the pump power and the energy detuning between photons and excitons.

pol


Microcavity polaritons, being made from fermionic particles and photons, have several special features. Due to the large wavelength of their photonic component and non-linearities associated with their under-lying fermionic structure the physics exits the regime of weakly interacting bosons at even modest density. Polaritons in planar microcavities are two-dimensional (2D) particles which can be trapped either in stress-induced harmonic potentials or in natural traps provided by microcavity disorder.

Coherence in a 2D polariton condensate


Below the superfluid transition in a 2D condensate we have bound vortex-antivortex pairs and power-law decay of first order spatial coherence g1

va

Above the transition vortex-antivortex pairs unbind and g1 decays exponentially

va2

How g1 decays in a polariton condensate which is also 2D can be found here:

  • Power-law decay of the spatial correlation function in exciton-polariton condensates
    Georgios Roumpos, Michael Lohse, Wolfgang H. Nitsche, Jonathan Keeling, Marzena Hanna Szymańska, Peter B. Littlewood, Andreas Löffler, Sven Höfling, Lukas Worschech, Alfred Forchel, and Yoshihisa Yamamoto
    PNAS (2012)

BEC of Polaritons in CdTe microcavities

First unambiguous demonstration of polariton BEC:

kasprzak

Occupation of different momentum (nearer image) and energy/momentum (further image) states across the condensation transition from left (uncondensed) to right (condensed).

  • Phase diagram for condensation of microcavity polaritons: From theory to practice
    F. M. Marchetti, M. H. Szymańska, J. Keeling, J. Kasprzak, R. André, Le Si Dang, P. B. Littlewood
    Phys. Rev. B 77, 235313 (2008)
  • Coherence properties and luminescence spectra of condensed polaritons in CdTe microcavities
    M. H. Szymańska, F. M. Marchetti, J. Keeling, P. B. Littlewood
    Solid State Commun. 144, 364 (2007)
  • Bose-Einstein condensation of exciton polaritons
    J. Kasprzak, M. Richard, S. Kundermann, A. Baas, P. Jeambrun, J. M. J. Keeling, F. M. Marchetti, M. H. Szymańska, R. Andre, J. L. Staehli, V. Savona, P. B. Littlewood, B. Deveaud, Le Si Dang
    Nature 443, 409 (2006)

Condensation in nonequilibrium driven-dissipative system: laser-BCS-BEC crossover

  • Keldysh Green’s function approach to coherence in a non-equilibrium steady state: connecting Bose-Einstein condensation and lasing
    J. Keeling, M. H. Szymańska, P. B. Littlewood
    chapter in Optical Generation and Control of Quantum Coherence in Semiconductor Nanostructures  
    Springer-Verlag, ISBN: 978-3-642-12490-7, arXiv:1001.3338 (2010)
  • Mean field theory and fluctuation spectrum of a pumped, decaying Bose-Fermi system across the quantum condensation transition
    M. H. Szymańska, J. Keeling, P. B. Littlewood
    Phys. Rev. B 75, 195331 (2007)
  • Non-equilibrium quantum condensation in an incoherently pumped dissipative system
    M. H. Szymańska, J. Keeling, P. B. Littlewood
    Phys. Rev. Lett. 96, 230602 (2006)
  • Polariton condensation and lasing in optical microcavities: The decoherence-driven crossover
    M. H. Szymańska, P. B. Littlewood, B. D. Simons
    Phys. Rev. A 68, 013818 (2003)
  • The crossover between lasing and polariton condensation in optical microcavities
    M. H. Szymańska, P. B. Littlewood
    Solid State Commun. 124, 103 (2002)

Disorder and Polariton BEC

  • Absorption, Photoluminescence and Resonant Rayleigh Scattering Probes of Condensed Microcavity Polaritons
    F. M. Marchetti, J. Keeling, M. H. Szymańska, P. B. Littlewood
    Phys. Rev. B 76, 115326 (2007)
  • Thermodynamics and excitations of condensed polaritons in disordered microcavities
    F. M. Marchetti, J. Keeling, M. H. Szymańska, P. B. Littlewood
    Phys. Rev. Lett. 96, 066405 (2006)

BCS-BEC crossover in microcavities

General