Indistinguishability of emitted photons from a semiconductor quantum dot in a micropillar cavity

1
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
2
Motivation

• Production of indistinguishable single photons
• Toolbox for quantum optics experiments
• Linear optics quantum computation

Photon-based two-qubit gates
3
Single quantum dots
InAs
GaAs
3 nm
4
Spectroscopy of single quantum dots
E
Artificialatoms
GaAs
Wetting layer

• Sharp spectral lines at low temperature (lt 30
  meV)
• Dephasing mechanisms (phonon, electrostatic)

Dot
GaAs
InAs
1400
1200
Emission of single photons
1000
800

• Pumping on an excited state of the exciton one
  e-h pair
• Spectral filtering of the X line

Intensity (arb. units)
600
InAs
400
200
900
910
920
930
940
950
960
Wavelength (nm)
5
Generation of single photons
Start Detector
50/50 Beamsplitter
1 photon
Stop Detector
1,0
0,8
0,6
g(2)(t)
0,4
0,2
0,0
-20
-10
0
10
20
Delay t (ns)
6
Indistinguishable Photons

• Characteristics
• Same polarization mode
• Same spatial mode
• Same spectral-temporal mode

Purest state of light
Negligible jitter (trelax 10 ps) compared with
pulse duration No phase diffusion (T2) during
the pulse duration
7
Indistinguishable Photons

• Key parameters

For indistinguishable photons T2 2 T1
Coherence time T2 Dephasing (phonons,
electrostatic...) Pure dephasing time T2
Lifetime T1
1
t
300 ps
T1 1.2 ns
T2
1/T2 1/2T1
8
Indistinguishable Photons - T1 shortening

• Cavity effects (Purcell)

Cavity Quantum Electrodynamics (CQED)
Control of the interaction
We modify the EM environment EM modes of a
microcavity
We use an isolated emitter X transition of a
single QD
9
Indistinguishable Photons - T1 shortening

• Cavity effects (Purcell)

Enhanced spontaneous emission into the cavity
mode
Leakage spontaneous emission into free space

120
104
100
80
103
60
F
Q
40
102
20
0
10
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
Diameter (mm)
10
Indistinguishable Photons
3
A single photon on a beamsplitter
1
4
11gt 02gt r 13gt 04gt t 03gt 14gt
2
01gt 12gt t 13gt 04gt - r 03gt 14gt
A single photon on each input arm of a
beamsplitter
11gt 12gt
t2 13gt 14gt - r2 13gt 14gt rt 23gt 04gt -
rt 03gt 24gt
Both photons go the same way coalescence into
a two-photon state
11
Indistinguishable Photons

• Experimental set-up

Stop
Time-interval counter
2 ns
Spectro- -meter
Spectro- -meter
Start
2 ns
Sample
12
Indistinguishable Photons

• Experimental set-up

Photon 2
Peak at dt0 (Long-Short)
Photon 1
Peak at dt4 ns (Short-Long)
Photon 1
4 ns
Photon 2
Peak at dt2 ns (Long-Long or Short-Short)
2 ns
Photon 2
Photon 1
13
Indistinguishable Photons

• Experimental set-up

For indistinguishable photons
Peak at dt0 (Long-Short)
Photon 2
Photon 1

Number of events
0
-2
2
4
-4
dt (ns)
14
Indistinguishable Photons
600
500
400
Number of events
300


200
100
0
-20
-10
0
10
20
Photon separation dt (ns)
Strongly reduced probability (ideally 0) of
simultaneous detection of two photons (i.e. one
on each output arm) The photons coalesce
two-photon state
15
Direct measurement of T1 and T2
T2 100ps
16
Indistinguishable Photons

• Mandel dip

J. Bylander, I. Robert-Philip, and I. Abram, Eur.
Phys. J. D 22, (2003) 295-301
1,0
0,8
0,6
g(2) (t)
0,4
0,2
0,0
-300
-200
-100
0
100
200
300
Time delay t (ps)
T1 90ps T2 100ps and T2
225ps F 15 Coalescence efficiency 55
17
Indistinguishable Photons

• Mandel dip

T1 60 - 110 ps T2 200 - 660 ps F
15-25 Best coalescence efficiency 76
18
Resonant condition of Purcell effect
140
24
20
120
16
Lifetime (ps)
100
12
Purcell Factor
8
80
4
60
0
0
2
-4
-2
0
2
4
Detuning (Angstroms)
19
Temperature dependence
Detuning (Å)
3.3 2.9 2.8 0
-2.2
1.0
1.0
500
500
400
400
0.8
0.8


T
T
2
2
g
g
300
300
0.6
0.6
(2)
(2)
Characteristic times (ps)
(0)
(0)
0.4
200
0.4
200
Characteristic
100
100
0.2
0.2
T
T
1
1
0.0
0.0
0
0
0
10
20
30
40
50
0
10
20
30
40
50
Temperature (K)
20
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...)