Microcavity Exciton-Polariton
Neil Na (那允中)
Institute of Photonics Technologies
National Tsing-Hua University
5/3/2012
Neil Na / Semiconductor Quantum Optoelectronics Group 2
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 3
• 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 4
QW excitons
• Wannier exciton:
free Hamiltonian screened Coulomb potential
Wannier
approximation
Neil Na / Semiconductor Quantum Optoelectronics Group 5
hole
electron
excitons are bosonic
at low-density limit
Neil Na / Semiconductor Quantum Optoelectronics Group 6
• QW interband transition
heterojunction
dispersion
we consider only interband
transition in this presentation!
Neil Na / Semiconductor Quantum Optoelectronics Group 7
• 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 8
• DBR cavity:
Microcavity photons
small mode volume &
large quality factor can
be achieved
Neil Na / Semiconductor Quantum Optoelectronics Group 9
• Dispersion & effective mass
~10-4mex
Neil Na / Semiconductor Quantum Optoelectronics Group 10
• 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 11
Strong coupling regime: exciton-polariton
• Strong coupling
upper
polariton
lower
polariton
photon
fraction
exciton
fraction
Neil Na / Semiconductor Quantum Optoelectronics Group 12
• Comparison between atomic & polaritonic cavity QED
Neil Na / Semiconductor Quantum Optoelectronics Group 13
• Rabi splitting & oscillation
Neil Na / Semiconductor Quantum Optoelectronics Group 14
• 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 15
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 16
• 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 (mpolariton~ 10-4mpolariton ~ 10-7matom)
– 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 17
• Complications by time-scales
Neil Na / Semiconductor Quantum Optoelectronics Group 18
• 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 19
• 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 20
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 21
• First evidence of dynamic condensation (Science 2002)
– Nonlinear threshold
Neil Na / Semiconductor Quantum Optoelectronics Group 22
– 2nd order coherence: g2(0) measurement
• Problems:
– Small pump angle
– Circular polarization
– Multimode g2(0) measurement & quantum depletion
thermal?
coherent?
Neil Na / Semiconductor Quantum Optoelectronics Group 23
• Polariton laser v.s. photon laser
Neil Na / Semiconductor Quantum Optoelectronics Group 24
• 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 25
Equilibrium Polariton BEC
• First evidence of equilibrium polariton BEC (Nature 2006)
nonlinear
threshold
ground
state
coherence
nonlinear
interaction
momentum space narrowing
Neil Na / Semiconductor Quantum Optoelectronics Group 26
linear polarization
1st order coherence
massive occupancy
Neil Na / Semiconductor Quantum Optoelectronics Group 27
• 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 28
Beyond EBC
• Bogoliubov excitation (Nature 2008) • Quantized vortices (Nature 2008)
Neil Na / Semiconductor Quantum Optoelectronics Group 29
• Superfluid (Nature 2009)
• Vortex - anti-vortex pair (Nature 2012)
Neil Na / Semiconductor Quantum Optoelectronics Group 30
• 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 31
• Bose-Hubbard model
Bose-Hubbard & Fermi-Hubbard model
Neil Na / Semiconductor Quantum Optoelectronics Group 32
Neil Na / Semiconductor Quantum Optoelectronics Group 33
• Fermi-Hubbard model
Neil Na / Semiconductor Quantum Optoelectronics Group 34
• 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 35
Higher-orbital state condensation
• Accessing weakly interacting regime is much easier experimentally
• S & P wave condensation (Nature 2007)
Neil Na / Semiconductor Quantum Optoelectronics Group 36
far field interference
Neil Na / Semiconductor Quantum Optoelectronics Group 37
• D wave condensation (Nature 2011)
metallic aperture
bandstructure
reciprocal space
far field image
Neil Na / Semiconductor Quantum Optoelectronics Group 38
• 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 39
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