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SUMMARY:Spin-Josephson coupling and the phase diagram of polariton condens
 ate arrays - Prof. Jeremy Baumberg NanoPhotonics Centre\, Cavendish Labora
 tory\, University of Cambridge
DTSTART:20190304T153000Z
DTEND:20190304T163000Z
UID:TALK118555@talks.cam.ac.uk
CONTACT:Kayleigh Dunn
DESCRIPTION:Polaritons are light-matter quasiparticles which exist within 
 wavelength-scale microcavities that couple confined photons with semicondu
 ctor excitons. Over the last decades these bosons have been found to exhib
 it nonequilibrium Bose-Einstein condensation\, with interaction energies s
 ufficient to give room temperature condensates. Here we will show how adva
 nces now allow arrays of interacting condensates to be explored\, and show
  the crucial role of magnetization in some situations. We show the unusual
  spontaneous symmetry breaking for the magnetisation of a polariton conden
 sate.[1\,2] Unpolarised incoherent pumping generates randomly spin-up or s
 pin-down magnetised condensates on each realisation\, which remain stable 
 for seconds\, but can be rapidly switched sub-ns. By applying an electrica
 l field perpendicular to the quantum-well plane we precisely tune the pola
 risation of the condensate emission. We utilise this to realise an electri
 cal spin-switch\, operating at record ultra-low switching energies of the 
 order of attojoules and switching speeds that are only limited by the cond
 ensate dynamics (hundreds of picosecond).[3] The direction of the spin of 
 two neighbouring condensates can also be controllably aligned (ferromagnet
 ic) or anti-aligned (antiferromagnetic) by optically tuning their coupling
  strength. Building on this\, we recently realized an optically controlled
  lattice of spin-polarized polariton condensates where we observe ferromag
 netic and antiferromagnetic phases\, and at the crossover between these tw
 o phases an unusual paired-spin phase.[4] We also observe new array intera
 ctions of condensates\, showing how coherence evolves across the entire ar
 ray. These properties\, which are due to the non-equilibrium and non-linea
 r nature of polariton condensates\, give strong hopes for a whole variety 
 of optoelectronic devices as well as outlining a completely new route towa
 rds utilising non-linear non-equilibrium coupled polariton condensates for
  complex simulations.\n\n[1]Phys. Rev. X 5\, 031002 (2015)\, H Ohadi et al
 \, Spontaneous spin bifurcations and ferromagnetic phase transitions in a 
 spinor exciton-polariton condensate\n[2]PRL 116\, 106403 (2016)\, H Ohadi 
 et al\, Tunable Magnetic Alignment between Trapped Exciton-Polariton Conde
 nsates \n[3]Nature Mat. 15\, 1074 (2016)\, A. Dreismann et al\, A sub-femt
 ojoule electrical spin-switch based on optically trapped polariton condens
 ates\n[4]PRL 119\, 067401 (2017)\, H Ohadi et al\, Spin Order and Phase Tr
 ansitions in Chains of Polariton Condensates
LOCATION:Ryle Seminar Room (930) 
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