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Experimental work on entangled photon holes T.B. Pittman, S.M. Hendrickson, J. Liang, and J.D. Franson UMBC ICSSUR Olomouc, June 2009 Experimental work on entangled photon holes T.B. Pittman, S.M. Hendrickson, J. Liang, and J.D. Franson UMBC ICSSUR Olomouc, June 2009 Linear Optics Quantum Computing, Zeno Gates Entangled-Photon Holes Outline Entangled Photon holes? Generation of these states by two-photon absorption quantum interference Experimental observation of photon holes using quantum interference Towards Bell’s inequality tests Optical Entanglement Entanglement of photon pairs: polarization momentum …. ….combinations of properties Polarization entanglement from Type II PDC (Kwiat ‘95) We are investigating a new form of entanglement arises from the absence of photon pairs themselves correlated absences…. “Entangled photon holes” Creation of entangled photon holes can have macroscopic effects on two-photon absorption effects of entanglement can be observed with “classical detector” This talk will focus instead on the basic concept and recent experimental work What are entangled photon holes? parametric down-conversion First, consider photon pairs from typical PDC scenario: Photons generated at same time, but that time is uncertain superposition of these times entanglement background in each beam is empty but uniform probability amplitude to find photon pair anywhere What are entangled photon holes? Two-photon absorption medium 3 2 1 weak coherent state inputs (3-level atoms) Now consider ideal two-photon absorption Photons annihilated at same time, but that time is uncertain superposition of these times entanglement Background in each beam is constant But uniform probability amplitude to find hole pair anywhere Consider two single-photon inputs “holes” correlated in time, but could be generated at any time: photon 1 amplitude coherent superposition photon 2 coinc. rate time - 0 + (t1-t2) PDC with narrowband pump photon pair could be produced at any time amplitude photon 1 coherent superposition of these times photon 2 coinc. rate time - 0 + (t1-t2) Photon pairs vs. Photon holes empty background photon pair anywhere constant background hole pair anywhere Entangled photon holes: “negative image” of PDC Ideal two-photon absorption? 3 Generation of entangled photon holes in this way requires strong two-photon absorption at the single-photon level Very difficult to achieve (works in progress) example system: tapered optical fiber in atomic vapor Can entangled photon holes be generated through quantum interference instead? Yes 2 1 (3-level atoms) TPA in tapered optical fibers Rb atoms optical fiber evanescent field outside fiber “heat and pull”: sub-wavelength diameter wires evanescent field interacts with Rubidium vapor Reduced mode volume beats optimal free-space focusing (for TPA) Recent experiments with tapered optical fibers in Rb d ~ 125 mm taper: d ~ 450 nm (over L ~ 5 mm) gives ~106 improvement in TPA rate over focused beam even this is way too small for observing TPA at single-photon levels! H.You et.al. PRA 78, 053803 (2008) Side note: nonlinear transmission through TOF Nonlinear transmission Rb atoms tend to accumulate on TOF can be removed using optical beam propagating through the TOF Reduces transmission (scattering) probably LIAD & thermal effects results in nonlinear transmission % S.M. Hendrickson et.al. JOSA B 26, 267 (2009) S. Spillane et.al PRL 100, 233602 (2008) saturation spectroscopy Photon holes via quantum interference ? weak coherent state Interference effect to suppress the probability P11 of finding one photon in each output mode? Photon holes via quantum interference PDC source 50/50 beam splitter phase locked, weak coherent state Interference effect to suppress the probability P11 of finding one photon in each output mode? mix with phase-locked PDC source at 50/50 BS Note: TPA case: classical in nonlinearity quantum out this case: classical in + quantum in interference quantum out Photon holes via quantum interference PDC source 50/50 beam splitter what is P11 ? phase locked, 1,1 ~ 2 1,1 ei 2 1,1 weak coherent state due to 2-photon term of weak coherent state due to PDC pair If indistinguishable amps and = p, destructive interference (P11 = 0) suppress any pairs from “splitting” at 50/50 leaves photon hole pairs in constant laser background experimental challenge: how to phase-lock PDC & weak laser? answer: Koashi et.al. phase-coherence experiment (1994) frequency-doubled laser (2w) for PDC pump PDC pairs at w fundamental (w) as weak coherent state MZ-like interferometer phase Versatile method: many implementations possible… Koashi et.al. PRA (1994) Resch et.al. two-photon switch PRL 87, 123603 (2001) Kuzmich et.al. homodyned Bell-test PRL 85, 1349 (2000) Lu and Ou, cw experiment PRL 88, 023601 (2002) Photon holes experiment laser pick-off PDC crystal SHG “HOM” beam splitter delay filter mode-locked laser primary beam splitter PDC APD-2 delay APD-1 ND l-plate PBS laser stop filters start data aq. TAC Photon holes experiment “HOM dip” V~99% laser pick-off PDC crystal SHG “HOM” beam splitter delay filter mode-locked laser primary beam splitter PDC APD-2 delay APD-1 ND l-plate PBS laser stop filters start data aq. TAC Photon holes experiment “HOM dip” V~99% laser pick-off PDC crystal SHG “HOM” beam splitter delay filter mode-locked laser primary beam splitter PDC APD-2 delay APD-1 ND l-plate PBS laser stop filters start giant MZ interferometer (fiber and free-space) data aq. key point: phase TAC step 1: calibration coinc. counts coincidence counts 2000 1500 matched two-photon amplitudes 2000 weak laser only (76 MHz pulse train) PDC only 1500 1000 1000 500 500 0 0 -20 0 20 40 -20 relative delay (ns) 0 20 40 step 2: phase control coinc. counts = 0o = 180o Visibility ~90% step 3: observation of photon holes Probability of finding one photon in each beam is suppressed coincidence counts coinc. counts 2000 1500 1000 500 0 Note: not completely eliminated. due to imperfect mode-matching -20 0 20 40 relative delay (ns) Pittman et.al. PRA 74, 041801R (2006) Data summary laser only main result PDC only Data summary laser only PDC only Important: data collected shows existence of photon holes, but does not demonstrate entangled nature of state -- analogous to just measuring “photon pairs” in, say, Kwiat ’95 polarization experiments additional measurements are required: -- Bell test with entangled photon holes main result Bell’s inequality tests basic idea: use “Franson interferometer” 1 L S coinc. counts S L 2 PDC source only S1S2 and L1 L2 amplitudes Rc ~ cos 2 1 2 2 can be used to violate Bell’s ineq. Bell’s inequality tests basic idea: use “Franson interferometer” 1 L S coinc. counts S L 2 PDC source photon holes source only S1S2 and L1 L2 amplitudes Photons never emitted at same time only S1L2 and L1S2 amplitudes Rc ~ cos 2 1 2 2 can be used to violate Bell’s ineq. Rc ~ cos 2 1 2 2 Bell’s inequality tests Interpretation is difficult: detectors only register background photons basic idea: use “Franson interferometer” -- photon holes suppress detection process in a nonlocal way 1 L S coinc. counts S L 2 PDC source photon holes source only S1S2 and L1 L2 amplitudes Photons never emitted at same time only S1L2 and L1S2 amplitudes Rc ~ cos 2 1 2 2 can be used to violate Bell’s ineq. Rc ~ cos 2 1 2 2 Time-bin entangled photon holes Photon hole generation: relies on interference of independent sources short-pulsed lasers/narrowband filters for indistinguishability no cw “energy-time” type entanglement this puts our Bell test exp’s into the “time-bin” regime (Gisin’s group) Experiments currently underway (4 stabilizations req’d) Time-bin entangled photon holes photon hole source Photon hole generation: relies on interference of independent sources short-pulsed lasers/narrowband filters for indistinguishability no cw “energy-time” type entanglement this puts our Bell test exp’s into the “time-bin” regime (Gisin’s group) Experiments currently underway (4 stabilizations req’d) Summary and outlook New form of entanglement entangled photon holes “negative image” of PDC Generation via ideal TPA or quantum interference effects recent experiments Many open questions: … quantum communications … Some comments on photon hole data Data looks similar to that typically obtained by splitting a conventional anti-bunched state PDC But that kind of (two-beam) state is very different than photon hole states of interest here 50/50 beam splitter -lock 1 laser excitation pulse train statistics of either beam resemble a coherent state splitting an antibunched beam gives two antibunched states >> also different than the (single-mode) states produced by “hole-burning” in Fock space: B. Basiea et.al. Phys. Lett A 240, 277 (1998) >> and not the same as the two-mode single-photon states of the form |0,1> + | 1,0> (HISTORICAL SIDE NOTE) Bouwmeester et.al. Teleporation Nature 390, 575 (1997) Koashi et.al. PDC phase coherence PRA 50, R3605 (1994) 1st demo that required “Multi-photon” experimental conditions Ultra-fast pulsed-PDC and narrowband filters for indistinguishability now used for many experiments Rarity et.al. PDC & |> Philos. Trans. 355, 2567 (1997) Fiber-based interferometer primary beam splitter HOM & primary beam splitters PDC photons weak laser pulse HOM beam splitter Rb TPA frequency-locking system 5 2D5/2 6 2P3/2 778 nm 420 nm optimal PDC bandwidth ~ 3 nm Doppler-broadened peaks ~ 1 GHz ~ 2 nm PDC lock 5 2P3/2 fluor. counts (arb) 778 nm 780 nm 5 2S1/2 Doppler-free peaks 0.0 0.5 1.0 1.5 2.0 2.5 3.0 laser frequency scan (GHz) spectral analysis wavelength meter SM fiber MM fiber 778 nm input fluorescence collection PBS aux. output beam l/4 Rb vapor cell in TC’d oven narrowband filter detector (SPCM or PIN) f = 80 mm lenses 3.5 4.0