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 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 We are investigating a new form of entanglement  arises from the absence of photon pairs themselves  correlated absences…. “Entangled photon holes” Polarization entanglement from Type II PDC (Kwiat ‘95)

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? 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 parametric down-conversion

What are entangled photon holes? 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 Two-photon absorption medium weak coherent state inputs

Consider two single-photon inputs “holes” correlated in time, but could be generated at any time: coherent superposition

PDC with narrowband pump photon pair could be produced at any time coherent superposition of these times

Photon pairs vs. Photon holes Entangled photon holes: “negative image” of PDC  empty background  photon pair anywhere  constant background  hole pair anywhere

Ideal two-photon absorption? 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

TPA in tapered optical fibers  “heat and pull”: sub-wavelength diameter wires  evanescent field interacts with Rubidium vapor evanescent field outside fiber Rb atoms Reduced mode volume beats optimal free-space focusing (for TPA) optical fiber

Recent experiments with tapered optical fibers in Rb  gives ~10 6 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, (2008) taper: d ~ 450 nm (over L ~ 5 mm) d ~ 125  m

Side note: nonlinear transmission through TOF  Rb atoms tend to accumulate on TOF  Reduces transmission (scattering)  can be removed using optical beam propagating through the TOF  probably LIAD & thermal effects  results in nonlinear transmission % Nonlinear transmission saturation spectroscopy S.M. Hendrickson et.al. JOSA B 26, 267 (2009) S. Spillane et.al PRL 100, (2008)

Photon holes via quantum interference Interference effect to suppress the probability P 11 of finding one photon in each output mode? ?

Photon holes via quantum interference mix with phase-locked PDC source at 50/50 BS Interference effect to suppress the probability P 11 of finding one photon in each output mode? Note: TPA case: classical in  nonlinearity  quantum out this case: classical in + quantum in  interference  quantum out

Photon holes via quantum interference what is P 11 ? If indistinguishable amps and  = , destructive interference (P 11 = 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 ( 2  ) for PDC pump  PDC pairs at   fundamental (  ) as weak coherent state  MZ-like interferometer  phase 

Versatile method: many implementations possible… Koashi et.al. PRA (1994) Kuzmich et.al. homodyned Bell-test PRL 85, 1349 (2000) Resch et.al. two-photon switch PRL 87, (2001) Lu and Ou, cw experiment PRL 88, (2002)

Photon holes experiment stop start TAC dataaq. APD-2 -1 primary beam splitter mode-locked laser SHG PDC crystal ND delay filter -plate PBS  filters “HOM” beam splitter laser pick-off PDC laser

Photon holes experiment stop start TAC dataaq. APD-2 -1 primary beam splitter mode-locked laser SHG PDC crystal ND delay filter -plate PBS  filters “HOM” beam splitter laser pick-off PDC laser “HOM dip” V~99%

Photon holes experiment stop start TAC dataaq. APD-2 -1 primary beam splitter mode-locked laser SHG PDC crystal ND delay filter -plate PBS  filters “HOM” beam splitter laser pick-off PDC laser “HOM dip” V~99% giant MZ interferometer (fiber and free-space) giant MZ interferometer (fiber and free-space) key point: phase 

step 1: calibration weak laser only (76 MHz pulse train) PDC only relative delay (ns) coincidence counts matched two-photon amplitudes

step 2: phase control   = 180 o   = 0 o Visibility ~90%

step 3: observation of photon holes Probability of finding one photon in each beam is suppressed Note: not completely eliminated. due to imperfect mode-matching Pittman et.al. PRA 74, R (2006)

Data summary main result laser only PDC only

Data summary main result 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  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

PDC source  only S 1 S 2 and L 1 L 2 amplitudes  can be used to violate Bell’s ineq. Bell’s inequality tests basic idea: use “Franson interferometer”

photon holes source  Photons never emitted at same time  only S 1 L 2 and L 1 S 2 amplitudes PDC source  only S 1 S 2 and L 1 L 2 amplitudes  can be used to violate Bell’s ineq. Bell’s inequality tests basic idea: use “Franson interferometer”

photon holes source  Photons never emitted at same time  only S 1 L 2 and L 1 S 2 amplitudes PDC source  only S 1 S 2 and L 1 L 2 amplitudes  can be used to violate Bell’s ineq. Bell’s inequality tests basic idea: use “Franson interferometer”  Interpretation is difficult: detectors only register background photons -- photon holes suppress detection process in a nonlocal way

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 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) photon hole source

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  But that kind of (two-beam) state is very different than photon hole states of interest here 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) 1 st demo that required “Multi-photon” experimental conditions  Ultra-fast pulsed-PDC and narrow- band filters for indistinguishability  now used for many experiments Koashi et.al. PDC phase coherence PRA 50, R3605 (1994) Bouwmeester et.al. Teleporation Nature 390, 575 (1997) Rarity et.al. PDC & |  > Philos. Trans. 355, 2567 (1997)

Fiber-based interferometer HOM & primary beam splitters PDC photons HOM beam splitter primary beam splitter weak laser pulse

Rb TPA frequency-locking system