1. Measuring the Wave-Function of Broadband Bi-Photons
FRISNO 2013, Ein Gedi
Measuring the Wave-Function of Broadband Bi-Photons
Yaakov Shaked, Roey Pomeranz, Avi Pe’er
Rafi Vered, Lena Kirjner, Michael Rosenbluh
Physics Dept. and BINA center for nanotechnology, Bar Ilan University
$$ ISF, EU-IRG, Kahn Foundation
How to make a Ti:Sapphire laser tap-dance – Posters M17, T23

2. Outline Why ultra broadband photon pairs?
Measuring time-energy entanglement
HOM interference
SFG correlation
Measuring the two-photon phase with quantum pairwise interference
Non-classical nature – Fringe contrast
FWM – Observe the entire quantum-to- classical transition

3. Time-Energy Entangled Photons
non linear crystal
pump
signal
idler
The two-photon state (monochromatic pump)
the spectrum of a single photon is not defined
all we know is they sum to w_p
such a state is TE ent. We have a superposition of pairs of photons. The wider g(w) , the more pairs we got, the state is more ent.
The width is determined by the phase matching cond. AB mainlt focused on Broadband DC, highly ent.
Entanglement

4. Time-Energy Correlation
uncertainty relation
the two-photon wave function (monochromatic pump)
in time domain it means….mono->spread in this axis and broadband-> narrow~100fs
the temporal wavefunction depends only on the time dif, where G is the

5. “Single cycle” bi-photons
Ultra-Broadband bi-Photons
Zero Dispersion !
PPKTP
Pump
880nm
CCD
“Single cycle” bi-photons

6. Why ultra-broad photon pairs ?
Because there are so many of them !
Standard detection does not work
Need new schemes !

7. Measuring entanglement - HOM1 2 BS
Limitations:
Phase sensitivity, but no phase measurement
Only for indistinguishable photons
Not directly applicable for collinear configuration
in time domain it means….mono->spread in this axis and broadband-> narrow~100fs
the temporal wavefunction depends only on the time dif, where G is the

8. Measuring entanglement - SFG
Down-converting
crystal
up-converting
Pump 532nm
IR detector
SPCM
Beam dump
Computer
PRL 94, (2005) , PRL 94, (2005)
Efficient two-photon interaction
Limitations:
Phase sensitivity, but no phase measurement
Very low SFG efficiency ! (10-8)
in time domain it means….mono->spread in this axis and broadband-> narrow~100fs
the temporal wavefunction depends only on the time dif, where G is the

9. Quantum two-photon interference
What if we let the pump pass ?
“Frustrated Two-Photon Creation via Interference" , T. J. Herzog, J. G. Rarity, H. Weinfurt & A. Zeilinger, Phys. Rev. Lett. 72, (1993).
Pump laser (880nm)
CCD camera
Crystal 1
Crystal 2
Pump power meter
60%
100
150
200
250 50
300
Freq. [THz]
Intensity [Arb]
60%
SFG efficiency = 60% Inherent phase stability !

10. Reconstruct the spectral phase
100
150
200
250 5 10 15 20
300
Phase mismatch
Dispersion from the dielectric mirrors

11. Measure of the two-photon purity
What is non-classical ?
Classical fringe contrast A
Pump laser (880nm)
CCD camera B
Crystal 1
Crystal 2
Pump power meter A
Measure of the two-photon purity B

12. Now to FWM… Four Waves Mixing Down conversion non linear fiber
non linear crystal
non linear fiber
pump
signal
pump
signal
idler
idler ωi
energy
conservation
2ωp ωs ki
momentum
conservation
(phase matching) ks
2kp

13. Can cover the full Quantum-Classical transition
The Experiment
6ps
Ti:S Laser (6ps)
PCF
Spontaneously generated signal-idler (ASE)
Spectrometer
Pump filter
Different from supercontinnum generation! INCOHERENT – No comb
Dispersive window
Unique regime compared to CW – High gain
Can cover the full Quantum-Classical transition
Rafi Z. Vered, Michael Rosenbluh, and Avi Pe’er,
“Two-photon correlation of broadband-amplified spontaneous four-wave mixing”, Phys. Rev. A 86, (2012)

14. FWM and TWM – Differences…
Down conversion
Four Waves Mixing
Rescale equations
Generalized phase mismatch

15. FWM Gain Solution Correlation ? Signal/idler solution
Similar to 3-waves, but…
Gain only when Δk<0 !
Gain also when Δκ≠0 !
Correlation ?
Threshold pump intensity !

16. FWM results (Fresh) At zero dispersion - 784nm (Δk≈0) Classical
Threshold ?
Full Quantum-classical transition !
786nm
788nm

17. Conclusions A source of collinear “single cycle” bi-photons
Huge ‘Homodyne’ Gain in two-photon efficiency (~40%) with pump inserted into the 2nd crystal
Holographic measurement of the spectral phase of the bi-photons by pairwise interference
Fringe contrast is a quantum signature – “Measure quantum correlation by trying to undo it…”
Observation of the entire classical-quantum transition with FWM in fiber
Inherently stable collinear interferometer – No locking needed
Many things we don’t understand yet…