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

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

parametricdown-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-photonabsorption medium

weak coherentstate inputs

1

2

3

(3-level atoms)

1

2

3

1

2

3

(3-level atoms)

Consider two single-photon inputs

coin

c. ra

te

- 0 + (t1-t2)

coin

c. ra

te

- 0 + (t1-t2)

“holes” correlated in time, but could be generated at any time:

coherent superposition

time

ampl

itude

photon 1

photon 2

time

ampl

itude

photon 1

photon 2

PDC with narrowband pump

photon pair could be produced at any time

coherent superposition of these times

coin

c. ra

te

- 0 + (t1-t2)

coin

c. ra

te

- 0 + (t1-t2)

time

ampl

itude

photon 1

photon 2

time

ampl

itude

photon 1

photon 2

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

1

2

3

(3-level atoms)

1

2

3

1

2

3

(3-level atoms)

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 ~106 improvement in TPA rateover focused beam

even this is way too small for observingTPA at single-photon levels!

H.You et.al. PRA 78, 053803 (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, 233602 (2008)

Photon holes via quantum interference

Interference effect to suppress the probability P11 of finding one photon in each output mode?

weak coherent stateweak coherent state

?

Photon holes via quantum interference

mix with phase-locked PDC source at 50/50 BS

Interference effect to suppress the probability P11 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

phase locked,

PDC source

weak coherent state

50/50 beam splitter

phase locked,

PDC source

weak coherent state

50/50 beam splitter

Photon holes via quantum interference

what is P11 ?phase locked,

PDC source

weak coherent state

50/50 beam splitter

phase locked,

PDC source

weak coherent state

50/50 beam splitter

If indistinguishable amps and = , 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)

1,11,1~ 221,1 ie

due to 2-photon termof weak coherent state due to PDC pair

1,11,1~ 221,1 ie

due to 2-photon termof weak coherent state due to PDC pair

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, 123603 (2001)

Lu and Ou, cw experiment PRL 88, 023601 (2002)

Photon holes experiment

stopstart

TACdata aq.

APD-2

APD-1

primarybeam splitter

mode-lockedlaser

SHGPDC

crystal

ND

delay

delay

filter

-platePBS

filters

“HOM” beam splitterlaserpick-off

PDC

laser

Photon holes experiment

stopstart

TACdata aq.

APD-2

APD-1

primarybeam splitter

mode-lockedlaser

SHGPDC

crystal

ND

delay

delay

filter

-platePBS

filters

“HOM” beam splitterlaserpick-off

PDC

laser

“HOM dip”V~99%

Photon holes experiment

stopstart

TACdata aq.

APD-2

APD-1

primarybeam splitter

mode-lockedlaser

SHGPDC

crystal

ND

delay

delay

filter

-platePBS

filters

“HOM” beam splitterlaserpick-off

PDC

laser

“HOM dip”V~99%

giant MZ interferometer(fiber and free-space)

key point: phase

step 1: calibration

0

500

1000

1500

2000

-20 0 20 400

500

1000

1500

2000

-20 0 20 40

weak laser only(76 MHz pulse train)

PDC only

relative delay (ns)

coin

cide

nce

coun

ts

matched two-photon amplitudes

coinc.countscoinc.counts

step 2: phase control

= 180o

= 0o

Visibility ~90%

coinc.countscoinc.counts

step 3: observation of photon holes

coinc.countscoinc.counts

relative delay (ns)

coin

cide

nce

coun

ts0

500

1000

1500

2000

-20 0 20 40

relative delay (ns)

coin

cide

nce

coun

ts0

500

1000

1500

2000

-20 0 20 400

500

1000

1500

2000

0

500

1000

1500

2000

-20 0 20 40

Probability of finding one photon in each beam is suppressed

Note: not completely eliminated. due to imperfect mode-matching

Pittman et.al. PRA 74, 041801R (2006)

Data summary

main result

laser only PDC only

Data summary

main result

laser only PDC onlyImportant: 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 sourceonly S1S2 and L1 L2 amplitudes

can be used to violate Bell’s ineq.

Bell’s inequality tests

S

L

1

S

L

S

L

1

2

S

L

2

S

L

coinc.counts

S

L

1

S

L

S

L

1

2

S

L

2

S

L

coinc.counts

basic idea: use “Franson interferometer”

2cos~ 212

cR

photon holes sourcePhotons never emitted at same timeonly S1L2 and L1S2 amplitudes

PDC sourceonly S1S2 and L1 L2 amplitudes

can be used to violate Bell’s ineq.

Bell’s inequality tests

S

L

1

S

L

S

L

1

2

S

L

2

S

L

coinc.counts

S

L

1

S

L

S

L

1

2

S

L

2

S

L

coinc.counts

basic idea: use “Franson interferometer”

2cos~ 212

cR

2cos~ 212

cR

photon holes sourcePhotons never emitted at same timeonly S1L2 and L1S2 amplitudes

PDC sourceonly S1S2 and L1 L2 amplitudes

can be used to violate Bell’s ineq.

Bell’s inequality tests

S

L

1

S

L

S

L

1

2

S

L

2

S

L

coinc.counts

S

L

1

S

L

S

L

1

2

S

L

2

S

L

coinc.counts

basic idea: use “Franson interferometer”

2cos~ 212

cR

2cos~ 212

cR

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

50/50 beam splitter

laser 1

PDC

-lock-lock

50/50 beam splitter

laser 1

PDC

-lock-lock

>> 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)

1st 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

primarybeam splitter

weaklaser pulse

Rb TPA frequency-locking system

PBS /4

wavelength meter spectral analysis

narrowbandfilter

detector(SPCM or PIN)

fluorescencecollection

SM fiberMM fiber

778 nm input

aux. output beam Rb vapor cellin TC’d oven

f = 80 mm lenses

PBS /4

wavelength meter spectral analysis

narrowbandfilter

detector(SPCM or PIN)

fluorescencecollection

SM fiberMM fiber

778 nm input

aux. output beam Rb vapor cellin TC’d oven

f = 80 mm lenses

PBS /4

wavelength meter spectral analysis

narrowbandfilter

detector(SPCM or PIN)

fluorescencecollection

SM fiberMM fiber

778 nm input

aux. output beam Rb vapor cellin TC’d oven

f = 80 mm lenses

PBS /4

wavelength meter spectral analysis

narrowbandfilter

detector(SPCM or PIN)

fluorescencecollection

SM fiberMM fiber

778 nm input

aux. output beam Rb vapor cellin TC’d oven

f = 80 mm lenses

laser frequency scan (GHz)

fluor

. cou

nts

(arb

)

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Doppler-free peaks

Doppler-broadened peaks ~ 1 GHz

PDC lock

laser frequency scan (GHz)

fluor

. cou

nts

(arb

)

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 laser frequency scan (GHz)

fluor

. cou

nts

(arb

)

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Doppler-free peaks

Doppler-broadened peaks ~ 1 GHz

PDC lock

780 nm

778 nm

778 nm

420 nm

5 2D5/2

6 2P3/2

5 2S1/2

5 2P3/2

~ 2 nm

optimal PDCbandwidth ~ 3 nm

780 nm

778 nm

778 nm

420 nm

5 2D5/2

6 2P3/2

5 2S1/2

5 2P3/2

~ 2 nm

780 nm

778 nm

778 nm

420 nm

5 2D5/2

6 2P3/2

5 2S1/2

5 2P3/2

~ 2 nm

optimal PDCbandwidth ~ 3 nm