Pure-state, single-photon wave-packet generation by parametric down conversion in a distributed...
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Pure-state, single-photon wave-packet generation by parametric down conversion in a distributed
microcavityM. G. Raymer, Jaewoo Noh*
Oregon Center for Optics, University of Oregon
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I.A. Walmsley, K. Banaszek, Oxford Univ.-----------------------------------------------------------------
* Inha University, Inchon, Korea-----------------------------------------------------------------
ITR - [email protected]
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Single-Photon Wave-Packet
1
€
1 = dω ψ∫ (ω) 1 ω
Wave-Packet is a Superposition-state:
(like a one-exciton state)
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Interference behavior of Single-Photon Wave-Packets
At a 50/50 beamsplitter a photon transmits or reflects with 50% probabilities.
1
1
€
1 = dω ψ∫ (ω) 1 ω
Wave-Packet is a Superposition-state:
0
beam splitter
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Interference behavior of Single-Photon Wave-Packets
At a 50/50 beamsplitter a photon transmits or reflects with 50% probabilities.
1
0
€
1 = dω ψ∫ (ω) 1 ω
Wave-Packet is a Superposition-state:
1
beam splitter
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Single-Photon, Pure Wave-Packet States Interfere as Boson particles
1
1beam splitter
2
0
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Single-Photon, Pure Wave-Packet States Interfere as Boson particles
1
1beam splitter
0
2
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Spontaneous Parametric Down Conversion in a second-order nonlinear, birefringent crystal
Phase-matching (momentum conservation):
rkS +
rkI =
rkP ±π / L
rkS
rkI
rkP
pumpSignal V-Pol
Idler H-Pol
Energy conservation:ωS +ωI =ωP
red red blue
L
kz
frequency
P
VH
H-Pol
phase-matching bandwidth
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Correlated Photon-Pair Generation by Spontaneous Down Conversion (Hong and Mandel, 1986)
0 or 1
Monochromatic Blue Light
Red photon pairs
2nd-order Nonlinear optical crystal
ω+ω '=ωP
ωP
ω '
ω
0 or 1
Ψ 2P = dω C∫ (ω) 1SIGNAL ω 1IDLER ωP −ω
IDLER
SIGNAL
• Creation time is uncontrolled
• Correlation time ~ (bandwidth)-1
Perfect correlation of photon frequencies:
optional
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1
1
Correlated Photon-Pair Measurement (Hong, Ou, Mandel, 1987)
Time difference
2 or 0
0 or 2
Red photons
Nonlinear optical crystal
Time difference
Coincidence Rate
Correlation time ~ (bandwidth)-1
Creation time uncontrolled
MC Blue light
boson behavior
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1
1
trigger if n = 1
filter
Pulsed blue light
For Quantum Information Processing we need
pulsed, pure-state single-photon sources.
Create using Spontaneous Down Conversion and conditional detection:
shutter
nonlinear optical crystal
(Knill, LaFlamme, Milburn, Nature, 2001)
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1
trigger if n = 1
filter
Pulsed blue light
For Quantum Information Processing we need
pulsed, pure-state single-photon sources.
Create using Spontaneous Down Conversion and conditional detection:
shutter
nonlinear optical crystal
SIGNAL
(Knill, LaFlamme, Milburn, Nature, 2001)
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trigger
Pulsed Pump Spectrum has nonzero bandwidth
Ψ2P
= dω '∫ dω C∫ (ω,ω ') 1IDLER ω ' 1SIGNAL ω
Zero-Bandwidth Filter , 0
ωP
ω'
ω1IDLER '
1SIGNAL
→ dω∫ C(ω0 ,ω ) 1SIGNAL ωdetect signal
Pure-state creation at cost of vanishing data rate
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1
1
1
trigger
trigger
1Time difference
Coincidence Counts
Do single photons from independent SpDC sources interfere well? Need good time and frequency correlation.
large data rate
filter
Pulsed blue light
filter
random delay
vanishing data rate
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Goal : Generation of Pure-State Photon Pairs without using Filtering
Single-photon Wave-Packet States:
1 S0 = dω ψ 0∫ (ω) 1 Sω
1 I0 = dω φ0∫ (ω) 1 I ω
signal
idler
Ψ2P
= dω '∫ dω C∫ (ω,ω ') 1IDLER ω ' 1SIGNAL ω
= 1I 0⊗ 1
S 0
€
C(ω,ω ') = ψ 0 (ω) × φ0 (ω ')Want :
(no entanglement)
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Decomposition of field into Discrete Wave-Packet Modes. (Law, Walmsley, Eberly, PRL, 2000)
Ψ = vac + dω'∫ dω C∫ (ω,ω' ) 1 Sω 1 Iω'
Ψ = vac + λ jj
∑ 1 Sj ⊗ 1 I j
1 S j = dω ψ j∫ (ω) 1 Sω
1 I j = dω φ j∫ (ω) 1 Iω
Single-photon Wave-Packet States:
(Schmidt Decomposition)
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The Schmidt Wave-Packet Modes are perfectly correlated.
But typically it is difficult to measure, or separate, the Schmidt Modes.
Ψ = vac + λ jj
∑ 1 Sj ⊗ 1 I j
Mode Amplitude Functions: Mode spectra overlap.
No perfect filters exist, in time and/or frequency.
frequency
€
CS1(ω)
€
CS 2(ω)
€
CS 3(ω)
filter
1 S j = dω ψ j∫ (ω) 1 Sω 1 I j = dω φ j∫ (ω) 1 Iω
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Why does the state generally NOT factor?
€
Ψ2P
= dω'∫ dω C∫ (ω,ω ') 1SIGNAL ω 1IDLER ω '
≠ 1S 0⊗ 1
I 0
€
€
'
€
C(ω,ω ')
need to engineer the state to make it factor
Energy conservation and phase matching typically lead to frequency correlation
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Spontaneous Parametric Down Conversion inside a Single-Transverse-Mode
Optical Cavity
rkS
rkI
rkP
pump
Nonlinear optical crystal with wave-guide
1 mm
DOES NOT WORK
the problem:cavity FSR ~ 1/Lphase-matching BW ~ 10/L
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Spontaneous Parametric Down Conversion inside a Distributed-Feedback Cavity
4 mm
0.2 mm cavity
second-order nonlinear-optical crystal
pump
H-PolH-Pol idler
V-Pol signal
4 mm
Linear-index Distributed-Bragg Reflectors (DBR)
Linear-index wave-guide
• large FSR = c /(2x0.2 mm)• small phase-matching BW: ~ 10 c /(4 mm)
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0 =800 nm KG = 25206/mmn/n ~ 6x10-4 (k = 2/mm)
4 mm
DBR 99% mirror
SIMPLIFIED MODEL: Half-DBR Cavity
Reflectivity
frequency/1015
DBR band gap
0.2 mm cavity
cavity mode
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Quantum Generation in a Dielectric-Structured Cavity: Phenomenological Treatment
∂x2E(x,t) −∂t
2D(x,t) = J(x,t) = χ NL Ep (x,t)E *(x, t)Signal Source Pump
Frequency Domain:
∂x2 + ε (x,ω ) ω 2⎡⎣ ⎤⎦ %E(x,ω ) = %J(x,ω )
∂x2 + ε (x,ω )ω 2⎡⎣ ⎤⎦u(x,ω ) = 0 (modes)
space and frequency dependent electric permeability:
ε(x,ω ) = ε (x)n2 (ω )
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€
x
internal Signal, Idler modes
pump fieldinteraction
€
˜ E S (x,ω)
€
˜ E S (x,ω) = ˜ E VAC (x,ω) + uout(x,ω) dω'∫ C(ω,ω') ˆ a I† (ω')
0 L
€
C(ω,ω') = χ NL dx'0
L∫ ˜ E p (x ' ,ω +ω') uS *(x ' ,ω)uI * (x' ,ω')
€
˜ E p
two-photon amplitude
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Heisenberg Picture Schrodinger Picture
Ψ = vac + dω'∫ dω C∫ (ω,ω' ) 1 Sω 1 Iω'
€
C(ω,ω ') = α p (ω + ω') Φ(ω,ω ')Amplitude for Photon Pair Production:
€
Φ(ω,ω') = χ NL dx '0
L∫ uP (x ' ,ω +ω')uS *(x ' ,ω)uI * (x ' ,ω')
pump spectrum
Cavity Phase-Matching
pump mode internal Signal, Idler modes
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Type-II Collinear Spontaneous Parametric Down Conversion in a second-order nonlinear, birefringent crystal
Phase-matching (momentum conservation):
rkS +
rkI =
rkP ±π / L
rkS
rkI
rkP
pump Signal
Idler
Energy conservation:
ωS +ωI =ωP
red red blue
L
k
frequency
P
VH
H-PolH-Pol
V-Pol
phase-matching bandwidth
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P
I
S
0 kS kI kP
S = I = P/2
Birefringent Nonlinear Crystal, Collinear, Type-II, Bulk Phase Matched, with Double-
Period Grating:
KGS/2 KGI/2
kS + kI = kP
KTP -->
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0 L
• grating index contrast • crystal length L = 4 mm, giving kG L = 8• cavity length ~ 0.2mm• signal and idler fields are phase matched at degeneracy wavelength S = I = 800 nm • pump wavelength = 400 nm• pump pulse duration 10 ps
n / n = 5 ×10−4
KTP Crystal with Double Gratings
95% mirror
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’ ’
No Grating, No Cavity
’ ’
Two Gratingszo
om
in
Two Gratings
with Cavity
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’ ’
’
’
Two Gratings with Cavity
x Pump Spectrum zoom
in
(hi res)
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€
C(ω,ω ') = χ NL dx '0
L∫ ˜ E p (x ' ,ω +ω') uS * (x ' ,ω)uI * (x ',ω')
Schmidt-Mode Decomposition
Schmidt-mode eigenvalues for different values of cavity-mirror reflectivity r2r2 j=1 j=2 j=3 j=4 j=50.95 0.951 0.0196 0.0196 0.0044 0.00440.99 0.998 0.0007 0.0007 0.0002 0.0002
Ψ = vac + dω'∫ dω C∫ (ω,ω' ) 1 Sω 1 Iω'
Ψ = vac + λ jj
∑ 1 Sj ⊗ 1 I j
1 S j = dω ψ j∫ (ω) 1 Sω 1 I j = dω φ j∫ (ω) 1 Iω
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j=1 j=2
j=4j=3
frequency frequency
amplitude
DBR
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• For cavity-mirror reflectivity = 0.99, the central peak contains 99% of the probability for photon pair creation, without any external filtering before detection.
• If any idler photon is detected, then the signal photon will be in the first Schmidt mode with 99% probability.
• Promising for high-rate production of pure-state, controlled single-photon wave packets.
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CONCLUSIONS & DIRECTIONS:• Spontaneous Down Conversion can be controlled by modifying the density of states of vacuum modes using distributed cavity structures.• One can engineer the vacuum to create single-photon pairs in well defined, pure-state wave packets, with no spectral no spectral entanglemententanglement.• In the absence of detector filtering, detection of one of the pair leaves the other in a pure single-photon state. • Waveguide development at Optoelectronics Research Center (Uni-Southampton, Peter Smith)
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cavity 1
cavity 2
beamsplitter
photon pairweak single-mode squeezed
Alternative Scheme: Single-mode squeezers combined at a beam splitter