Www.bris.ac.uk Single photon sources. Attenuated laser = Coherent state Laser Attenuator Approximate...

Single photon sources

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

Pair photons and entangled photons

gEgvacaiga

aaaaaagH

Hi

t

pis

pispis

.exp

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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

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

Portable Crystal based entangled pair source150mW diode

70000 detected coincidences/sec

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

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

Experiment

Spectra

Coincidences~3.105 s-1

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

Recent HOM Experiment

Entangled state, preliminary measurement

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