Characterisation of non-classical
light sources for quantum
information technologies
Piotr Kolenderski
Robert Frankowski
Konrad Banaszek
Institute of Physics
Nicolaus Copernicus University
Toruń, Poland
Wojciech Wasilewski
Michał Karpiński
Piotr Wasylczyk
Czesław Radzewicz
Faculty of Physics
University of Warsaw
Poland
Parametric down-conversion
Energy conservation:
wp = ws + wi
Momentum conservation:
kp  ks + ki
s
p
i
Twin beams
Fibre coupling
Fourier Transform Spectroscopy
t
Common-path interferometer
Joint spectrum measurement
W. Wasilewski, P. Wasylczyk, P. Kolenderski, K. B., and C. Radzewicz,
Opt. Lett. 31, 1130 (2006)
Interferogram
-100
-80
-60
-40
-20
0
20
40
-80
60
-60
80
-40
100
-20
-100
-80
-60
-40
-20
0
20
40
60
80
0
20
40
60
80
100
-100
-80
-60
-40
-20
0
20
40
60
80
100
Experiment vs. theory
Schmidt decomposition




Mode pairs
…what about the mode of one photon?
Two-photon interference
Probability amplitudes:
&
–
+
–
Photon indistinguishability
= mode matching
Coincidence probability
&
Single pulse
t’
t
Double pulse
t’
t
Experimental scheme
M1
D1
fLO
BS1
M2
t1
BS2
D2
t2
ALO
W. Wasilewski, P. Kolenderski, and R. Frankowski,
Phys. Rev. Lett. 99, 123601 (2007)
&
r
Simulated interferogram
Fourier transform
Experimental setup
BS FL XSH IL DM
RegA
HWP
P
DM BG X
t1
FC
IF
D1
t
ND FC
FPC
W. Wasilewski, P. Kolenderski, and R. Frankowski,
Phys. Rev. Lett. 99, 123601 (2007)
50/50
D2
Results
Output wave function
Fiber coupling:
Brigthness:
Purity:
Optimization
Brightness
Purity
Geometric decorrelation:
A. U’Ren, K. B., and I. A.
Walmsley, Quant. Inf.
Comp. 3, 480 (2003).
P. Kolenderski,
W. Wasilewski, and K.B.,
arXiv:0905.0009
Phys. Rev. A (in press)
Spectral filtering
L = 1 mm, ws = wi = 100 mm, tp = 100 fs
Multiphoton statistics
Losses
Multimode model
losses


Squeezing strength r
Equivalent number of (equally
probable) modes
M
losses

Experimental setup
W. Wasilewski, C. Radzewicz, R. Frankowski, and K. Banaszek,
Phys. Rev. A 78, 033831 (2008)
Two-beam photon statistics
Equivalent number of modes
 no filters
 10 nm filters
+ 5 nm filters
Overall detection efficiency
 no filters
 10 nm filters
+ 5 nm filters
Contamination coefficients
Two-photon contamination
 no filters
 10 nm filters
+ 5 nm filters
Four-photon contamination
No interference filters
Non-linear waveguide
M. Karpiński,
C. Radzewicz, and K.B.,
Appl. Phys. Lett. 94,
181105 (2009)
Conclusions
• “Toolbox” for measuring spectral properties
• Modal structure an issue in multiphoton interference
• Spectral filtering sensible option for bulk sources
• Higher-order terms dangerous!