Microcavity Exciton-Polariton - PDF Free Download

Microcavity Exciton-Polariton Neil Na ( 那允中 ) Institute of Photonics Technologies National Tsing-Hua University 5/3/2012

Outline Microcavity Exciton-polariton QW excitons Microcavity photons Strong coupling regime: exciton-polariton Dynamic Condensation of Exciton-Polariton Dynamic polariton BEC Polariton laser Equilibrium Polariton BEC Beyond BEC Quantum simulator of many-body system Bose-Hubbard & Fermi-Hubbard model Higher-orbital state condensation Summary Neil Na / Semiconductor Quantum Optoelectronics Group 2

Microcavity Exciton-polariton QW excitons Microcavity photons Strong coupling regime: exciton-polariton Dynamic Condensation of Exciton-Polariton Dynamic polariton BEC Polariton laser Equilibrium Polariton BEC Beyond BEC Quantum simulator of many-body system Bose-Hubbard & Fermi-Hubbard model Higher-orbital state condensation Summary Neil Na / Semiconductor Quantum Optoelectronics Group 3

QW excitons Wannier exciton: free Hamiltonian screened Coulomb potential Wannier approximation Neil Na / Semiconductor Quantum Optoelectronics Group 4

hole electron excitons are bosonic at low-density limit Neil Na / Semiconductor Quantum Optoelectronics Group 5

QW interband transition heterojunction we consider only interband transition in this presentation! dispersion Neil Na / Semiconductor Quantum Optoelectronics Group 6

Microcavity photons DBR cavity: small mode volume & large quality factor can be achieved Neil Na / Semiconductor Quantum Optoelectronics Group 8

Dispersion & effective mass ~10-4 m ex Neil Na / Semiconductor Quantum Optoelectronics Group 9

Strong coupling regime: exciton-polariton Strong coupling upper polariton photon fraction lower polariton exciton fraction Neil Na / Semiconductor Quantum Optoelectronics Group 11

Comparison between atomic & polaritonic cavity QED Neil Na / Semiconductor Quantum Optoelectronics Group 12

Rabi splitting & oscillation Neil Na / Semiconductor Quantum Optoelectronics Group 13

Dynamic polariton BEC Original proposal Polariton should condense below/above critical temperature/density A new type of coherent light source without population inversion condensed polariton thermal polariton Neil Na / Semiconductor Quantum Optoelectronics Group 15

Exciton BEC: Disorder, localization (inhomogeneous broadening) Dissociation of excitons (screening, phase space filling) Long lifetime of indirect exciton Polariton BEC: Extended phase coherence reinforced by a cavity field suppression of inhomogeneous broadening Binding energy enhancement by strong coupling reduce dissociation of excitons Extremely light effective mass very high condensation temperature (m polariton ~ 10-4 m polariton ~ 10-7 m atom ) Photonic component out-coupling from the cavity with k conservation in contrast to spontaneous decay of an un-dressed exciton direct experimental access to internal polariton population Short lifetime of microcavity photon Neil Na / Semiconductor Quantum Optoelectronics Group 16

Complications by time-scales Neil Na / Semiconductor Quantum Optoelectronics Group 17

Complications by excitation methods resonant pumping non-resonant pumping four-wave mixing: residual coherence from external laser relaxation bottleneck: sharp change of density of sttes Neil Na / Semiconductor Quantum Optoelectronics Group 18

Polariton laser It was shown that the bosonic final state stimulation is needed to overcome the bottleneck effect, i.e., reaching polariton lasing. Demonstration of bosonic final state stimulation Neil Na / Semiconductor Quantum Optoelectronics Group 20

First evidence of dynamic condensation (Science 2002) Nonlinear threshold Neil Na / Semiconductor Quantum Optoelectronics Group 21

2nd order coherence: g 2 (0) measurement thermal? coherent? Problems: Small pump angle Circular polarization Multimode g 2 (0) measurement & quantum depletion Neil Na / Semiconductor Quantum Optoelectronics Group 22

Polariton laser v.s. photon laser Neil Na / Semiconductor Quantum Optoelectronics Group 23

Equilibrium Polariton BEC First evidence of equilibrium polariton BEC (Nature 2006) nonlinear threshold momentum space narrowing ground state coherence nonlinear interaction Neil Na / Semiconductor Quantum Optoelectronics Group 25

massive occupancy linear polarization 1 st order coherence Neil Na / Semiconductor Quantum Optoelectronics Group 26

Beyond EBC Bogoliubov excitation (Nature 2008) Quantized vortices (Nature 2008) Neil Na / Semiconductor Quantum Optoelectronics Group 28

Superfluid (Nature 2009) Vortex - anti-vortex pair (Nature 2012) Neil Na / Semiconductor Quantum Optoelectronics Group 29

Bose-Hubbard & Fermi-Hubbard model Bose-Hubbard model Neil Na / Semiconductor Quantum Optoelectronics Group 31

Neil Na / Semiconductor Quantum Optoelectronics Group 32

Fermi-Hubbard model Neil Na / Semiconductor Quantum Optoelectronics Group 33

Higher-orbital state condensation Accessing weakly interacting regime is much easier experimentally S & P wave condensation (Nature 2007) Neil Na / Semiconductor Quantum Optoelectronics Group 35

far field interference Neil Na / Semiconductor Quantum Optoelectronics Group 36

D wave condensation (Nature 2011) bandstructure metallic aperture reciprocal space far field image Neil Na / Semiconductor Quantum Optoelectronics Group 37

Summary The field of exciton-polariton vastly expanded in the past decade. Although it is an open dissipative system, many features of bosons in equilibrium can be similarly observed. In additional to fundamental scientific research, numerous practical applications have also been proposed. Future directions: BEC - BCS crossover Polariton meditated superconductivity Polaritonics THz generation Nonclassical photon generation Neil Na / Semiconductor Quantum Optoelectronics Group 39