www.bris.ac.uk single photon sources. attenuated laser = coherent state laser attenuator approximate...
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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
)(
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.