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

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

S. Varoutsis

LPN Marcoussis

S. Laurent, E. Viasnoff, P. Kramper & M. GallardL. Le Gratiet, C. Mériadec, L. FerlazzoI. Sagnes, A. Lemaître, I. Robert-Philip, I. Abram

LABORATOIRE DE PHOTONIQUE ET DE NANOSTRUCTURES

Motivation Production of indistinguishable single photons

Toolbox for quantum optics experiments

Linear optics quantum computation

Photon-basedtwo-qubit gates


Single quantum dots

InAs

GaAs

3 nm


Spectroscopy of single quantum dots

Sharp spectral lines at low temperature (< 30 eV)

Dephasing mechanisms (phonon, electrostatic)

“Artificial”atoms

InAs

Pumping on an excited state of the exciton : one e-h pair

Spectral filtering of the X line

Emission of single photons

GaAs

InAs

EGaAs

Wetting layer

Dot

900 910 920 930 940 950 960

200

400

600

800

1000

1200

1400

Inte

ns

ity

(a

rb.

un

its

)

Wavelength (nm)

0

Laser at 888nmT ~4K


Generation of single photons

1 photon

StartDetector

StopDetector

50/50 Beamsplitter

T ~ 12.2 ns

2T 3T 3TT T

Start

Stop

0 T 2T 3T 4T

Nb

of

coi

ncid

ence

s

Delay t1

2

3

-20 -10 0 10 20

0,0

0,2

0,4

0,6

0,8

1,0

g(2) (t

)

Delay t (ns)


Indistinguishable Photons Characteristics

Same polarization mode Same spatial mode Same spectral-temporal mode

Purest state of light

Pump pulse Pump pulse Pump pulse

time

Negligible jitter (relax ~10 ps) compared with pulse duration

No phase diffusion (T2) during the pulse duration


Key parameters :

Indistinguishable Photons

For indistinguishable photons : T2 = 2 T1

t T1 ~ 1.2 ns

Lifetime : T1Coherence time :T2

Dephasing (phonons, electrostatic...)

Pure dephasing time T2*

T2 = 1/T2* + 1/2T1

1~ 300 ps


Indistinguishable Photons - T1

shortening Cavity effects (Purcell)

Cavity Quantum Electrodynamics (CQED)

We use an isolated emitter

X transition of a single QD

We modifythe EM environment

EM modes of a microcavity

Control of the interaction


Indistinguishable Photons - T1

shortening Cavity effects (Purcell)

F = = + 3 Q 0

3

0 42 V n3 0

Enhanced spontaneous emission into the cavity mode

Leakage spontaneous emission into free space

0

20

40

60

80

100

120

10

102

103

104

0 1 2 3 4 5 6 7 8 90 1 2 3 4 5 6 7 8 9

Q F

Diameter (m)



│11> │12> t2 │13> │14> - r2 │13> │14> + rt │23> │04> - rt │03> │24>

│11> │02> r │13> │04> + t │03> │14>

│01> │12> t │13> │04> - r │03> │14>

A single photon on a beamsplitter

A single photon on each input arm of a beamsplitter

Both photons go the same way : «coalescence» into a two-photon state

1

2

3

4


Indistinguishable Photons Experimental set-up

Time-interval counter

Spectro--meter

Sample

Stop

Start

2 ns

Spectro--meter

2 ns



Photon 2

Photon 1

4 nsPhoton 1

Photon 2

2 nsPhoton 2

Photon 1

Peak at t=0(Long-Short)

Peak at t=4 ns(Short-Long)

Peak at t=2 ns

(Long-Long orShort-Short)

0 2 4-2-4 t (ns)

Number of events



For indistinguishable photons

+

0 2 4-2-4 t (ns)

Number of events

Photon 1

Photon 2

Peak at t=0(Long-Short)



Num

ber

of e

vent

s

Strongly reduced probability (ideally 0) of simultaneous detection of two photons (i.e. one on each output arm)

The photons coalesce two-photon state

-20 -10 0 10 200

100

200

300

400

500

600

Photon separation t (ns)


Direct measurement of T1 and T2

-40 0 40 80 120 1600,0

0,2

0,4

0,6

0,8

Vis

ibili

ty

Time (ps)

1,0

T2 ~ 100ps

-200 0 200 400 600 800

0

1000

2000

3000

4000

5000

6000

Inte

nsi

ty (

arb

. unit

s)

Time (ps)

T1 ~ 90ps


Indistinguishable Photons Mandel dip

212

2

1

*2

2

1

2)2(

2221

21)( TTT ee

T

Te

T

T

RT

RTg

T1 ~ 90ps T2 ~ 100ps and T2* ~ 225ps F ~15 & Coalescence efficiency ~ 55%

Photon 2

Photon 1

J. Bylander, I. Robert-Philip, and I. Abram, Eur. Phys. J. D 22, (2003) 295-301

-300 -200 -100 0 100 200 3000,0

0,2

0,4

0,6

0,8

1,0

g(2

) ()

Time delay (ps)

Theoretical prediction for: T1 = 90ps and T2 = 100ps Experimental Data


Indistinguishable Photons Mandel dip

T1 ~ 60 - 110 ps T2* ~ 200 - 660 ps

F ~15-25Best coalescence efficiency ~ 76%

-400 -200 0 200 4000,0

0,2

0,4

0,6

0,8

1,0

Delay (ps)

g(2

) ()


Resonant condition of Purcell effect

0 260

80

100

120

140

-4 -2 0 2 40

4

8

12

16

20

24Li

feti

me (

ps)

Pu

rcell Fa

ctor

Detuning (Angstroms)


Temperature dependence

3.3 2.9 2.8 0 -2.2Detuning (Å)

g(2

)(0)

0.0

0.2

0.4

0.6

0.8

1.0

0 10 20 30 40 500

100

200

300

400

500

Chara

cteri

stic

T2*

T1

g(2

)(0)

0.0

0.2

0.4

0.6

0.8

1.0

0 10 20 30 40 500

100

200

300

400

500

Chara

cteri

stic

tim

es

(ps)

Temperature (K)

T2*

T1


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...)

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

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