Characterisation of non-classical light sources for quantum information technologies

Characterisation of non-classical light sources for quantum information technologies

Wojciech WasilewskiMichał KarpińskiPiotr Wasylczyk

Czesław RadzewiczFaculty of Physics

University of WarsawPoland

Piotr KolenderskiRobert FrankowskiKonrad BanaszekInstitute of PhysicsNicolaus Copernicus UniversityToruń, Poland

Parametric down-conversionParametric down-conversion

sp

i

Energy conservation:

Momentum conservation:

p = s + i

kp ks + ki

Twin beamsTwin beams

Fibre couplingFibre coupling

Fourier Transform SpectroscopyFourier Transform Spectroscopy

Common-path interferometerCommon-path interferometer

Joint spectrum measurementJoint spectrum measurement

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

InterferogramInterferogram

-100 -80 -60 -40 -20 0 20 40 60 80

-100

-80

-60

-40

-20

0

20

40

60

80

100

-100 -80 -60 -40 -20 0 20 40 60 80 100

-80

-60

-40

-20

0

20

40

60

80

100

Experiment vs. theoryExperiment vs. theory

Schmidt decompositionSchmidt decomposition

Mode pairsMode pairs

…what about the mode of one photon?

Two-photon interferenceTwo-photon interference

&

Probability amplitudes:

– + –

Photon indistinguishability =

mode matching

Coincidence probabilityCoincidence probability

&

Single pulseSingle pulse

t

t’

Double pulseDouble pulse

t

t’

Experimental schemeExperimental scheme

fLO

ALOr

t1 t2

&BS1 BS2

D2

D1M1

M2

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

Simulated interferogramSimulated interferogram

Fourier transformFourier transform

Experimental setupExperimental setup

RegA

t1

t

X

FP C 50/ 50

D 1

D 2

I F

FC

D M

BGD M

I LFL

FC

PHW P

BS XSH

ND

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

ResultsResults

Output wave functionOutput wave function

Fiber coupling:

Brigthness: Purity:

OptimizationOptimizationB

rig

htn

ess

Pu

rity

P. Kolenderski,W. Wasilewski, and K.B.,arXiv:0905.0009Phys. Rev. A (in press)

Geometric decorrelation:

A. U’Ren, K. B., and I. A. Walmsley, Quant. Inf. Comp. 3, 480 (2003).

Spectral filteringSpectral filtering

L = 1 mm, ws = wi = 100 mm, p = 100 fs

Multiphoton statisticsMultiphoton statistics

Losses

Multimode modelMultimode model

losses

losses Equivalent number of

(equally probable) modes

M

Squeezing strength r

Experimental setupExperimental setup

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

Two-beam photon statisticsTwo-beam photon statistics

Equivalent number of modesEquivalent number of modes

no filters 10 nm filters + 5 nm filters

Overall detection efficiencyOverall detection efficiency

no filters 10 nm filters + 5 nm filters

Contamination coefficientsContamination coefficients

Two-photon contaminationTwo-photon contamination

no filters 10 nm filters + 5 nm filters

Four-photon contaminationFour-photon contamination

No interference filters

Non-linear waveguideNon-linear waveguide

M. Karpiński, C. Radzewicz, and K.B.,Appl. Phys. Lett. 94,181105 (2009)

ConclusionsConclusions

• “Toolbox” for measuring spectral properties

• Modal structure an issue in multiphoton interference

• Spectral filtering sensible option for bulk sources

• Higher-order terms dangerous!