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Harnessing light-matter interaction in intersubband microcavities
NEST CNR-INFM and Scuola Normale SuperiorePisa, Italy
Aji A. Anappara
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People involved in this workDavid Barate, Alessandro Tredicucci, Lucia Sorba
and Fabio Beltram NEST CNR-INFM & Scuola Normale Superiore, Pisa, Italy
Simone De Liberato and Cristiano CiutiUniv. Paris 7-Denis Diderot, Paris, France
Giorgio BiasiolNEST CNR-INFM and Laboratorio TASC, Trieste, Italy
Jan Devenson, Roland Teissier
and Alexei BaranovIES, Montpellier II, France
Carl Hübler
and Rupert Huber Universitaet
Konstanz, Konstanz, Germany
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Outline
Introduction and motivation
Strong-coupling regime using intersubband transitions
Manipulation of cavity electrodynamics
‘Ultra-strong coupling regime’ of light-matter interaction
Attempts to realize ultra-strong coupling regime
Conclusions
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How intersubband
transitions interact with confined electromagnetic field?
Intersubband photonicsA
bsor
ptio
n
350
5−
x2
x2 150+
250 x
E
k||
“atomic-like”ultrafast relaxation time (~ps ) tailorable properties
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Cavity QED
cavdg E=Transition-photon coupling,
coupling
Optical cavity light resonator⇒
Electronic transition material resonance⇒
Weak coupling Strong coupling
Perturbative regimePurcell effect
Rabi oscillations“cavity-polaritons”
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Light-matter interaction
1
2
0ω1
2 2 Ω
0ωcavitymode ≡
electronic transition weak coupling strong coupling
⇒
1
2g
γ
κ
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Strong-coupling regime
Solid state physics:
excitons (bulk, QWs or QDs in semiconductor microcavities)
qubits (cooper pair quantum-box in microwave resonators)
Atomic physics: atoms in metallic microcavity
R. J. Thompson et al., PRL.,68, 1132 (1992)
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Exciton polaritons
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Intersubband resonatorsTheoretical predictions by Ansheng
Liu, PRB., 55, 7101 (1997)
θintGaAs
substrate
cavity core
airθcav
z
DBR
QWs
air
DBR
substrate
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Intersubband resonators
Ansheng
Liu, PRB 55, 7101 (1997)
Lcav
= 3μm; NDBR
= 3 GaAs/AlAs
DBRsTotal thickness ~ 14 μm
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total-internal reflection geometryair as top-cladding
D. Dini
et.al, PRL., 90, 116401 (2003)
Intersubband polaritons
θ
AlAs
cavity core
60°
GaAssubstrate
Lcav
~ 3μm; θcav
= 60°;
NQW
= 18, doped to 5×1011cm-2
LAlAs
~ 4 μm;
Total thickness ~ 5 μm
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0.850 0.855 0.860 0.865 0.870 0.875 0.880
110
120
130
140
150
160
170
angle θ (degrees)58.5 59.0 59.5 60.0 60.5 61.0 61.5 62.0
Ener
gy (m
eV)
sin(θ)
Intersubband polaritons
D. Dini
et.al, PRL., 90, 116401 (2003)
measurements at 10K
100 120 140 160 180
61.9861.6361.2560.6160.32
60.1360.0560.0059.7659.4959.2858.90
58.3858.37
58.20
Reflectance (a. u.)
Energy (meV) 12
, 2 14
, 140
Minimum splitting meV
ISBT energy meVω
Ω =
=
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105 120 135 150 165 180
Ref
lect
ance
(a. u
.)
Energy (meV)
62.0
61.5
61.0
60.5
60.0
59.5
59.0
58.5
58.0
100 120 140 160
0.3
0.4
0.5
0.6
0.7
Ref
lect
ance
Energy (meV)
Coupled oscillators -
simulationElectromagnetic field propagation : Optical transfer matrix
Quantum well : ( ) ( )2 2
2 2
0 0 0
1
eff
Ne f Sin
m L i
θε ω ε
ε ω ω γω∞= +
− −
⎛ ⎞⎜ ⎟⎝ ⎠
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Intersubband resonators
0 1 2 3 4 50.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Fiel
d In
tens
ity
Growth direction (μm)
Cladding (AlAs)
Active region m
etal
(Au)
0 1 2 3 4 5 6 7
0.0
0.1
0.2
0.3
0.4
Active regionFi
eld
Inte
nsity
Growth direction (μm)
cladding(AlAs)
air
0 1 2 3 4 5 6 7
0.0
0.1
0.2
0.3
0.4
Cladding (AlAs)
Fiel
d In
tens
ity
Growth direction (μm)
Cladding (AlAs)
Active region
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Manipulation of cavity electrodynamics
intersubband polaritons, N → electron density
-
can be tuned externally !!
N → number of oscillators
Rabi splitting, NΩ∝
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Depletion gating
Ohmic contacts
Schottky
gate
Cavity core
θ
n-doped
GaAsAlAs 3 quantum
wells
70°
A. A Anappara
et al., APL., 87, 051105 (2005)
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Normal-mode splitting and anticrossing
90 100 110 120 130 140 150 160 170
Ref
lect
ance
(a.u
)
Energy (meV)
66.8967.0367.1867.3367.4767.6267.7767.9268.0768.2268.3768.4468.5268.6768.7468.8268.9769.1269.2769.4269.57
66.5 67.0 67.5 68.0 68.5 69.0 69.5 70.0112116120124128132136140144148
Ener
gy(m
eV)
Angle (θ)
12
, 2 13
, 137
Minimum splitting meV
ISBT energy meVω
Ω =
=
3300
QWsmeasured at K
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Strong coupling to weak coupling
A. A Anappara
et al., APL., 87, 051105 (2005)
105 120 135 150
-6V-5.5V
-5V-4.5V
-4V-3.5V
-3V-2.5V
-2V-1.5V
-1VRef
lect
ance
(a. u
.)
Energy (meV)
zero V-0.5V
Room temperature measurementsResonant angle, θ
= 68.67°
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Tunnel-assisted control of splitting
(b) 52 kV/cm
(c) 100 kV/cm
(a) Zero bias
A. A Anappara
et al., APL., 89, 171109 (2005)
Carriers are injected by tunneling
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100 120 140 160 180 200
Ref
lect
ance
(a.u
.)
Energy(meV)
68.1767.8767.5767.2766.9666.6766.3666.0765.7765.4765.1864.8964.59
64.0164.30
(a) Zero field
50 100 150 200 250 300
120 140 160
Ref
lect
ance
(a.u
.)
Energy(meV)
-7V-6.5V
-6V-5.5V
-5V-4.5V
-4V-3.5V
-3V-2.5V
-2V-1.5V
-1V-0.5VzeroV
68.7868.4868.1767.8767.5767.2766.9666.6766.3666.0765.7765.4765.1864.8964.59
64.01
Ref
lect
ance
(a.u
.)
Energy(meV)
64.30
(b)100kV/cm
Tuning by tunnel coupling
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Conclusions
Tailorability and manipulation of cavity electrodynamics
in intersubband microcavities
Intersubband microcavities are potential systems to realize
the unprecedented ‘ultra-strong coupling regime’
Novel device applications – high absorption QWIPs,
ultrafast optical switches, super luminescent devices