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

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

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

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

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

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

Measuring entanglement - HOM 1 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

Measuring entanglement - SFG Down-converting crystal up-converting Pump 532nm IR detector SPCM Beam dump Computer PRL 94, 043602 (2005) , PRL 94, 073601 (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

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, 629-632 (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 !

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

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

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

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, 043837 (2012)

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

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 !

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

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…