Transcript Document

Indistinguishability of emitted
photons from a semiconductor
quantum dot in a micropillar cavity
S. Varoutsis
LPN Marcoussis
S. Laurent, E. Viasnoff, P. Kramper & M. Gallard
L. Le Gratiet, C. Mériadec, L. Ferlazzo
I. Sagnes, A. Lemaître, I. Robert-Philip, I. Abram
Motivation

Production of indistinguishable single photons

Toolbox for quantum optics experiments

Linear optics quantum computation
Photon-based
two-qubit gates
LABORATOIRE
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Single quantum dots
InAs
GaAs
3 nm
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Spectroscopy of single quantum dots
E
“Artificial”atoms
GaAs
Wetting
layer
Dot
GaAs

InAs

Sharp spectral lines at low
temperature (< 30 meV)
Dephasing mechanisms
(phonon, electrostatic)
Intensity (arb. units)
1400
Laser at 888nm
T ~4K
1200
1000
Emission of single photons
800

600
400
200

0
900
910
920
930
940
950
Pumping on an excited state of
the exciton : oneInAs
e-h pair
Spectral filtering of the X line
960
Wavelength (nm)
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Generation of single photons
T ~ 12.2 ns
Start
Detector
50/50 Beamsplitter
1 photon
Start
Stop
Detector
2T
T
3T
3T
T
1,0
Stop
Nb of
coincidences
g(2)(t)
0,8
0,6
0,4
3
0,2
2
0,0
1
Delay t
0
T
2T
3T
4T
-20
-10
0
10
Delay t (ns)
20
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Indistinguishable Photons

Characteristics



Same polarization mode
Same spatial mode
Same spectral-temporal mode
Purest state of light
time
Pump pulse
Pump pulse
Pump pulse
Negligible jitter (trelax ~10 ps) compared with pulse duration
No phase diffusion (T2) during the pulse duration
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Indistinguishable Photons

Key parameters :
For indistinguishable photons : T2 = 2 T1
Coherence time :T2
Lifetime : T1
Dephasing (phonons,
electrostatic...)
Pure dephasing time T2*
T1 ~ 1.2 ns
t
T2 =
1
~ 300 ps
1/T2* + 1/2T1
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Indistinguishable Photons - T1 shortening

Cavity effects (Purcell)
Cavity Quantum Electrodynamics (CQED)
We use an
isolated emitter
X transition of a single QD
Control of
the interaction
We modify
the EM environment
EM modes of a microcavity
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Indistinguishable Photons - T1 shortening

Cavity effects (Purcell)
g
F=
g0
=
3 Q l03
4p2
Enhanced spontaneous emission
into the cavity mode
V
n3
+
g1
g0
Leakage spontaneous
emission into free space
120
104
100
80
103
60
Q
102
F
40
20
10 0
1
2
3
4
5
6
7
8
9
0
Diameter (mm)
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Indistinguishable Photons
A single photon on a beamsplitter
│11> │02>
r │13> │04> + t │03> │14>
│01> │12>
t │13> │04> - r │03> │14>
3
4
1
2
A single photon on each input arm of a beamsplitter
│11> │12>
t2 │13> │14> - r2 │13> │14> + rt │23> │04> - rt │03> │24>
Both photons go the same way : «coalescence» into a two-photon state
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Indistinguishable Photons

Experimental set-up
Time-interval
counter
Stop
2 ns
Spectro-meter
Start
Spectro-meter
2 ns
Sample
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Indistinguishable Photons

Experimental set-up
Photon 2
Peak at dt=0
(Long-Short)
Photon 1
Number of events
Peak at dt=4 ns
(Short-Long)
Photon 1
4 ns
Photon 2
-4
-2
0
2
4
dt (ns)
Peak at dt=2 ns
2 ns
Photon 2
Photon 1
(Long-Long or
Short-Short)
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Indistinguishable Photons
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Experimental set-up
For indistinguishable photons
Peak at dt=0
(Long-Short)
Photon 2
Photon 1
+
Number of events
-4
-2
0
2
4
dt (ns)
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Indistinguishable Photons
Number of events
600
500
400
300
200
100
0
-20
-10
0
10
Photon separation dt (ns)
20
Strongly reduced probability (ideally 0) of simultaneous detection of two
photons (i.e. one on each output arm)
The photons coalesce
two-photon state
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Direct measurement of T1 and T2
1,0
0,8
Visibility
0,6
0,4
0,2
6000
Intensity (arb. units)
T2 ~ 100ps
T1 ~ 90ps
5000
4000
3000
2000
1000
0
0,0
-40
0
40
80
Time (ps)
120
160
-200
0
200
400
Time (ps)
600
800
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Indistinguishable Photons

Mandel dip
2RT  T2
( 2)
g (t )  1 
e
1  2RT  2T1

2 t
T2
T2*  T1

e e
2T1 

t
2 t
T2




J. Bylander, I. Robert-Philip, and I.
Abram, Eur. Phys. J. D 22, (2003)
295-301
1,0
Photon 2
t
Photon 1
g(2) (t)
0,8
0,6
0,4
0,2
0,0
Theoretical prediction for:
T1 = 90ps and T2 = 100ps
Experimental Data
-300 -200 -100
0
100 200
Time delay t (ps)
300
T1 ~ 90ps
T2 ~ 100ps and T2* ~ 225ps
F ~15 & Coalescence efficiency ~ 55%
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Indistinguishable Photons
Mandel dip
1,0
0,8
g(2) (t)

0,6
0,4
0,2
0,0
-400
-200
0
200
400
Delay t (ps)
T2* ~ 200 - 660 ps
F ~15-25
Best coalescence efficiency ~ 76%
T1 ~ 60 - 110 ps
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Resonant condition of Purcell effect
24
20
120
16
100
12
8
80
Purcell Factor
Lifetime (ps)
140
4
60
-4
-2
0
2
Detuning (Angstroms)
4
0
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500
Detuning (Å)
2.9
2.8
3.3
0 -2.2
400
300
1.0
0.8
T2*
0.6
200
0.4
100
0.2
g(2) (0)
Characteristic times (ps)
Temperature dependence
T1
0
0
10
20
30
40
0.0
50
Temperature (K)
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Conclusions

Generation of indistinguishable single photons



Toolbox for quantum optics experiments
Engineering of nanosources for photon-based quantum
information processing
Future prospect :

Generation of entangled photons to implement more
sophisticated functionalities of quantum information processing
(teleportation, quantum logic...)
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