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Single photon sources

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Page 1: Www.bris.ac.uk Single photon sources. Attenuated laser = Coherent state Laser Attenuator Approximate single photon source Mean number of photon per pulse

Single photon sources

Page 2: Www.bris.ac.uk Single photon sources. Attenuated laser = Coherent state Laser Attenuator Approximate single photon source Mean number of photon per pulse

Attenuated laser =Coherent state

Laser Attenuator Probability

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 1 2

Number of photon

Approximate single photon source

nnn

n

ennnp

nn

22 variance

!),(

photons ofon distributiPoisson

shows stateCoherent

Mean number of photon per pulse = 0,1

n

vace

2

22

2

...2!2

1

Page 3: Www.bris.ac.uk Single photon sources. Attenuated laser = Coherent state Laser Attenuator Approximate single photon source Mean number of photon per pulse

Pair photons and entangled photons

gEgvacaiga

aaaaaagH

Hi

t

pis

pispis

.exp

)(

Page 4: Www.bris.ac.uk Single photon sources. Attenuated laser = Coherent state Laser Attenuator Approximate single photon source Mean number of photon per pulse

Why photon pairs?• Heralded single photon source

Trigger photons

Source ofPhoton pairs

Heralded photons

Mandel (1986)Experimental realization of a localized one-photon state, C. K. Hong and L. Mandel, Phys. Rev. Lett. 56, 58 (1986)

Observation of sub-poissonian light in parametric downconversion. J.G. Rarity, P.R.Tapster and E. Jakeman,

Opt. Comm., 62(3):201, 1987.

Triggered APD

APD

321 Triggered

....3,32,21,1

232

33

221

gCgCN

gCgCgCvacN

JGR,JMO 1998, 45, 595-604

Page 5: Www.bris.ac.uk Single photon sources. Attenuated laser = Coherent state Laser Attenuator Approximate single photon source Mean number of photon per pulse

Creating Entangled Photon Pairs

idlersignalpump

idlersignalpump

www

kkk

0Phase matching and energy conservation:

Non-linearcrystal (type II)

Blue laser beam

Red photonpairs

A

BCrystal axis

C

D

).why! vacuum...(ignoring

B-A Pairs

D-C Pairs

21

BABA

DC

HVVH

VH

Page 6: Www.bris.ac.uk Single photon sources. Attenuated laser = Coherent state Laser Attenuator Approximate single photon source Mean number of photon per pulse

Portable Crystal based entangled pair source150mW diode

70000 detected coincidences/sec

Page 7: Www.bris.ac.uk Single photon sources. Attenuated laser = Coherent state Laser Attenuator Approximate single photon source Mean number of photon per pulse

Recent experimentsFree-Space distribution of entanglement and singlephotons over 144 km, R. Ursin, et al quant-ph/0607182

Page 8: Www.bris.ac.uk Single photon sources. Attenuated laser = Coherent state Laser Attenuator Approximate single photon source Mean number of photon per pulse

idlersignalpump

pidlersignalpump

www

Pkkk

2

022 Phase matching and energy conservation:

χ(3)kp

kp ki

ks

• Non-linear process in χ(3)

• 2 pump photons 2 emitted photons

Use of the normal dispersion region:

• no pump power dependence

• wavelengths created far from the pump

• Raman and fluorescence amplification effects reduced

W. J. Wadsworth et al. (Opt. Express 2004)

pump=709nm

idler=897nm

signal=587nm

Pair photon generation in microstructured fibresWith University of Bath

Page 9: Www.bris.ac.uk Single photon sources. Attenuated laser = Coherent state Laser Attenuator Approximate single photon source Mean number of photon per pulse

Experiment

Spectra

Coincidences~3.105 s-1

Page 10: Www.bris.ac.uk Single photon sources. Attenuated laser = Coherent state Laser Attenuator Approximate single photon source Mean number of photon per pulse

Confirmation of bright pair photon emission: -potential for 80% coupling to SMF

Coincidence resultsIdler (895nm): single-mode fiber ~ 14% of coincidences

Signal (583nm): multimode fiber ~ 33% of coincidences

: single-mode fiber ~ 22% of coincidences

Ppump=540μW:

• Coincidence rate: ~3.5.105 s-1

• Overall coupling efficiency in SMF 60%

2 photon peak

4 photon peak

Page 11: Www.bris.ac.uk Single photon sources. Attenuated laser = Coherent state Laser Attenuator Approximate single photon source Mean number of photon per pulse

Recent HOM Experiment

Page 12: Www.bris.ac.uk Single photon sources. Attenuated laser = Coherent state Laser Attenuator Approximate single photon source Mean number of photon per pulse

Entangled state, preliminary measurement

Latest result by narrow band filtering: 90% in HV and 80% in +/-45.