1. www.bris.ac.uk Single photon sources

2. Attenuated laser = Coherent state Laser Attenuator Approximate single photon source Mean number of photon per pulse = 0,1

3. www.bris.ac.uk Pair photons and entangled photons

4. Why photon pairs? Heralded single photon source Trigger photons Source of Photon 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 JGR,JMO 1998, 45, 595-604

5. Creating Entangled Photon Pairs Phase matching and energy conservation: C D

6. Portable Crystal based entangled pair source 150mW diode 70000 detected coincidences/sec

7. Recent experiments Free-Space distribution of entanglement and single photons over 144 km, R. Ursin, et al quant-ph/0607182

8. Phase matching and energy conservation: χ (3) kpkp kpkp kiki ksks 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 fibres With University of Bath

9. Experiment Spectra Coincidences~3.10 5 s -1

10. Confirmation of bright pair photon emission: -potential for 80% coupling to SMF Coincidence results Idler (895nm): single-mode fiber ~ 14% of coincidences Signal (583nm): multimode fiber ~ 33% of coincidences : single-mode fiber ~ 22% of coincidences P pump =540μW: Coincidence rate: ~3.5.10 5 s -1 Overall coupling efficiency in SMF 60% 2 photon peak 4 photon peak

11. Recent HOM Experiment

12. Entangled state, preliminary measurement Latest result by narrow band filtering: 90% in HV and 80% in +/-45.