1. Characterisation of non-classical light sources for quantum information technologies Wojciech Wasilewski Michał Karpiński Piotr Wasylczyk Czesław Radzewicz Faculty of Physics University of Warsaw Poland Piotr Kolenderski Robert Frankowski Konrad Banaszek Institute of Physics Nicolaus Copernicus University Toruń, Poland

2. Parametric down-conversion Energy conservation: Momentum conservation:  p =  s +  i k p  k s + k i

3. Twin beams

4. Fibre coupling

5. Fourier Transform Spectroscopy 

6. Common-path interferometer

7. Joint spectrum measurement W. Wasilewski, P. Wasylczyk, P. Kolenderski, K. B., and C. Radzewicz, Opt. Lett. 31, 1130 (2006)

8. Interferogram

9. Experiment vs. theory

10. Schmidt decomposition    

11. Mode pairs …what about the mode of one photon?

12. Two-photon interference & Probability amplitudes: – + – Photon indistinguishability = mode matching

13. Coincidence probability &

14. Single pulse t t’

15. Double pulse t t’

16. Experimental scheme W. Wasilewski, P. Kolenderski, and R. Frankowski, Phys. Rev. Lett. 99, 123601 (2007)

17. Simulated interferogram

18. Fourier transform

19. Experimental setup W. Wasilewski, P. Kolenderski, and R. Frankowski, Phys. Rev. Lett. 99, 123601 (2007)

20. Results

21. Output wave function Fiber coupling: Brigthness: Purity:

22. Optimization Brightness Purity P. Kolenderski, W. Wasilewski, and K.B., arXiv:0905.0009 Phys. Rev. A (in press) Geometric decorrelation: A. U’Ren, K. B., and I. A. Walmsley, Quant. Inf. Comp. 3, 480 (2003).

23. Spectral filtering L = 1 mm, w s = w i = 100 mm,  p = 100 fs

24. Multiphoton statistics Losses

25. Multimode model  losses  Equivalent number of (equally probable) modes M Squeezing strength r

26. Experimental setup W. Wasilewski, C. Radzewicz, R. Frankowski, and K. Banaszek, Phys. Rev. A 78, 033831 (2008)

27. Two-beam photon statistics

28. Equivalent number of modes   no filters  10 nm filters+ 5 nm filters

29. Overall detection efficiency   no filters  10 nm filters+ 5 nm filters

30. Contamination coefficients

31. Two-photon contamination   no filters  10 nm filters+ 5 nm filters

32. Four-photon contamination No interference filters

33. Non-linear waveguide M. Karpiński, C. Radzewicz, and K.B., Appl. Phys. Lett. 94, 181105 (2009)

34. Conclusions “Toolbox” for measuring spectral properties Modal structure an issue in multiphoton interference Spectral filtering sensible option for bulk sources Higher-order terms dangerous!