gap optique geneva university 1 quantum communication with 1 photon: q cryptography with 2...
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Quantum Communication
With 1 photon: Q cryptography
With 2 photons: Q crypto, Bell tests, qutrits, plasmons
With 3 photons: Q teleportation
With 4 photons: entanglement swapping
News from the industry forehead
Nicolas Gisin Hugo Zbinden, Ivan Marcikic, Hugues de Riedmatten,
Sylvain Fasel, Jeroen van Houwelingen, Rob Thew
Group of Applied Physics, University of Geneva
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Q communication in optical fibres
The transmission depends on the wavelength- Lower attenuation : 1310 nm (0.3 dB/km) and 1550 nm
(0.2dB/km) (telecom wavelengths)
Two problems : Losses and decoherence. How to minimize them ?
Time-bin coding with
Decoherence due to birefringence : Polarization Mode Dispersion
photons at telecom wavelength
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Time-bin qubits
qubit :
any qubit state can be created
and measured in any basis
variable coupler variable coupler
1 0
h
Alice Bob
D0
D1
switchswitch
1
0
10 10 iecc
0
1
2
10
2
10
2
1i0
2
1i0
10 10 iecc
State preparation Projective measurement
W. Tittel & G. Weihs, Quant. Inf. Comput. 1, Number 2, 3 (2001)
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BA
i
BAecc 1100
10
B
0A
01
B
1A
Detectors &Coincidence
Time-bin entanglement
PDC
Laser Variable coupler
Robust against decoherence
in optical fibers
0 20 40 60 80 1000
50
100
150
200
250
Noise level
coin
cide
nces
[/1
0s]
phase[arb unit]
After 2x2km of optical fibers
2 km optical fibers
V net =96% Photon pair creation in a non-linear
crystal
Parametric down-conversion (PDC)
Energy and momentum conservationispisp kkk
p=710nms=1310nm
i=1550nm
R. Thew et al., Phys. Rev. A 66, 062304 (2002)
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1-photon: Q cryptoAlice Bob
*2-
31 km
Siftedkey rate
OpticalQBER
Accident.QBER
DetectorQBER
Dispers.QBER
TotalQBER
Compensation 23 Hz 5.5 % 1 % 4 % 0 % 10.5 %Interf. Filter 11 Hz 4 % 1 % 1.7 % 0.5 % 7.2 %
Results: (PRA 63,012309, 2001 and S. Fasel et al., EJPD 30, 143, 2004)
CDCIF
Asynchronous heraldedsingle-photon source
TDC-like measurement (normalized)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-5 -4 -3 -2 -1 0 1 2 3 4 5
bin
Time between a click at detector A and a click at detector B [# trigger signals]
Num
ber
of e
vent
s ( n
orm
ailz
ed)
P(1)=60% P(2)=0.02% g(2)(0)=0.0012 34 KHz(quant-ph/0408136)
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A -1
A 1
B -1
B 1
2 5 k m S O F 2 5 k m D S F
2-photons: Bell test over 50 km2-photons: Bell test over 50 km
BobAlice
Bp00
Bp11
Bp10
Bp01
Time arrival on A1
Ap00
Ap11
Ap10
Ap01
Time arrival on B1
0 = short path
1 = long path
BABA
11002
1
Type I NLCCreating photons @ 1.3 & 1.55 m
deterministic sepation with WDM coupler
)cos(1),( ijVPij
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Idea: verify from time to time the phase
10800 10820 10840 10860 10880 10900 10920 10940
0
1
2
3
4
5
Stabilisation period~ 5 [s]
Measuring period~ 100 [s]
Inte
nsi
ty [
arb
. u
nits
]
Time [s]
Stabilisation of the interferometersStabilisation of the interferometers
APD
WDM
BS
FM
FM
EPRSource
PIN
Stabilised laser
Feedback
Phase controlerSwitch
Every 100 s the phase is brought back to a given value
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Bell test over 50 kmBell test over 50 km
With phase control we can choose four different settings = 0° or 90° and = -45° or 45°
Violation of Bell inequalities:)45,90()45,0()45,90()45,0( EEEES
0.0 0.2 0.4 0.6 0.8 1.0 1.2-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
Co
rre
latio
n F
un
ctio
n
Time [h]
006.0518.0)45,0( E
0.0 0.2 0.4 0.6 0.8 1.0 1.2-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
Co
rre
latio
n F
un
ctio
n
Time [h]
005.0554.0)45,90( E
0.0 0.2 0.4 0.6 0.8 1.0 1.2-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
Cor
rela
tion
Fun
ctio
n
Time [h]
006.0533.0)45,0( E
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
Co
rre
latio
n F
un
ctio
n
Time [h]
007.0581.0)45,90( E
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
Co
rre
latio
n F
un
ctio
n
Time [h]
012.0185.2 SViolation of Bell inequalities
by more than 15
Marcikic et al., PRL, in press, quant-ph/0404124
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2-photons: Qutrit Entanglement
llecmmecssc llmm ii )(2
)(10
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Bell Violation with qutrits
I = 2.784 +/- 0.023
I(lhv) = 2 < I(2) = 2.829 < I(3) = 2.872
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2-photons: Plasmon assisted entanglement transfer
In collaboration with Prof. Erni, Zürich
SS+LL
SLLS
difference of detection tim e
eve
nts
TAC
150 m
G old 200nm th ick
700nm
300nm
Co
inci
de
nce
s
Phase Phase
phase
Reference fringesVisib ility : 90%
Plasm on assistedVisib ility : 90%
Co
inci
de
nce
s
a short lived phenomenon like a plasmon can be coherently excited at two times that differ by much more than its lifetime. At a macroscopic level this would lead to a “Schrödinger cat” living at two epochs that differ by much more than a cat’s lifetime.
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3 photons: Q teleportation & Q relays
EPR
Bell
2 bitsU
0.80
0.82
0.84
0.86
0.88
0.90
0.92
0.94
0.96
0.98
1.00
0 50 100 150 200 250 300 350
Distance [km]
Fid
eli
ty
n=1 n=2 n=3 n=4
Alice Charlie
EPR source
Bob
BSM
Classical channel
2 km 2 km 2 km
J. D. Franson et al, PRA 66,052307,2002Collins et al.,quant-ph/0311101
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Q repeaters & relays
*entanglement
*entanglement
entanglement
Bellmeasurement
. .
QND measurement+ Q memory
*entanglement
*entanglement
Bellmeasurement
.??
RE
PE
AT
ER
R
EL
AY
H. Briegel, W. Dür, J. I. Cirac and P. Zoller, Phys. Rev. Lett. 81, 5932 (1998)
J. D. Franson et al, PRA 66,052307,2002; D. Collins et al., quant-ph/0311101
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2 km of optical fiber 2 km of optical fiber
AliceAlice:creation of qubits to be teleportedAliceAlice:creation of qubits to be teleported
AliceAlice
55 m
BobBob:analysis of the teleported qubit, 55 m from Charlie
BobBob:analysis of the teleported qubit, 55 m from Charlie
BobBob
CharlieCharlie:the Bell measurementCharlieCharlie:the Bell measurement
CharlieCharliefs laser @ 710 nmfs laser @ 710 nm
Experimental setupExperimental setup
creation of entangled qubitscreation of entangled qubits
coincidence electronicscoincidence electronics
&
LBO
RG
WDM
RG
WDM
GeInGaAs
LBO
BS
InGaAs
fs l
aser
sync out
1.3
m 1.3m
1.5 m
1.5 m
2km 2km
2km
H. de Riedmaten et al.,PRL 92, 047904-1/4, 2004
I. Marcikic et al., Nature, 421, 509-513, 2003
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resultsresults
0 2 4 6 8 10 12 14 16 18
0
5
10
15
20
25
30
35
40
0 2 4 6 8 10 12 14 16 18
0
5
10
15
20
25
30
35
40
fou
r-fo
ld c
oin
cid
ence
s [1
/50
0s]
Phase [arb. units]
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
Th
ree-
fold
co
inci
den
ce [
/500
s]
fou
r-fo
ld c
oin
cid
ence
s [1
/50
0s]
Phase [arb. units]
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
Th
ree-
fold
co
inci
den
ce [
/500
s]
Equatorial statesEquatorial states
Raw visibility : VRaw visibility : Vrawraw= 55 = 55 ±± 5 %5 %
2V1F raweq = 77.5 = 77.5 ±± 2.5 % 2.5 %
1
0
1,0F
0,1F
= = 78 78 ± ± 3%3%
= = 77 77 ± ± 3%3%
North & south polesNorth & south poles
wrongcorrect
correct
CC
CF
mean fidelity: mean fidelity: FFpolespoles=77.5 =77.5 ±± 3 % 3 %
0 1 2 3 4 5 60.0
0.2
0.4
0.6
0.8
1.0
coin
cid
ence
[arb
un
it]
time between start and stop [ns]
3
1
3
2
peqmean FFF
77.5 ±2.5 %
Mean FidelityMean Fidelity
» 67 % (no entanglement)
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2 km of optical fiber 2 km of optical fiber
AliceAlice:creation of qubits to be teleportedAliceAlice:creation of qubits to be teleported
AliceAlice
55 m
BobBob:analysis of the teleported qubit, 55 m from Charlie
BobBob:analysis of the teleported qubit, 55 m from Charlie
BobBob
CharlieCharlie:the Bell measurementCharlieCharlie:the Bell measurement
CharlieCharliefs laser @ 710 nmfs laser @ 710 nm
Experimental setupExperimental setup
creation of entangled qubitscreation of entangled qubits
coincidence electronicscoincidence electronics
&
LBO
RG
WDM
RG
WDM
GeInGaAs
LBO
BS
InGaAs
fs l
aser
sync out
1.3
m 1.3m
1.5 m
1.5 m
2km 2km
2km
H. de Riedmaten et al.,PRL 92, 047904-1/4, 2004
On the same spool !
See Halder et alquant-ph/0408092
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A B C D
4-photons: Entanglement swapping
Bell state measurement
Entangled photons that never interacted
EPR source EPR source
BAi
BA e 1,10,0 )()( AB DC
iDC e 1,10,0 )()(
CD
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Sources of time-bin entangled photons
BAi
BAABe 1,10,0
2
1)(
BAi
BACDe 1,10,0
2
1)(
The experiment
Bell state measurement
CBCBBC0,11,0
2
1)(
CBCBi
AD)( 0,11,0e
21
Entanglement analysis
A lice B o b
Actively stabilized interferometers
1km1km
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In the experiment :Partial Bell state measurement
Entanglement swapping
)()( )()( CDABABCD
AD
i
BC
AD
i
BC
ADBC
ADBC
e
e
)()(
)()(
)()(
)()(
)2(
)2(
Four Bell states involved
in the experiment !
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Superposition basis: results
V = (80 ± 4) %F 90 %
78 hours of measurement !
100 200 300 400 500 6000
10
20
30
40
50
60
70
80
90
100
Four
-pho
ton
coin
cide
nces
[/6
h]
Phase [degrees]
0
1000
2000
3000
4000
5000
3-p
hoto
n co
inci
denc
es [
/6h]
with
out B
SM
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Results: computational basis
0
10
20
30
40
50
60
70
80
1 2 3 4
Fou
r ph
oton
coi
ncid
ence
s [
/ hou
r]
DA 0,0
DA 1,0DA 0,1
DA 1,1
%5.31.91
Total
CorrectMean Fidelity =
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News from the industry forehead
http://www.swissquantum.deckpoint.ch/embargo/index_en.php
Yesterday, September 29, id Quantique, DeckPoint and the University of Geneva officially inaugurated the first data archive site secured with Quantum Cryptography.
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Data archiving network secured byQuantum Crypto
10 km
http://www.swissquantum.deckpoint.ch/embargo/index_en.php
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Quantis: Quantum random numbers on demand (www.randomnumbers.info)
4 Mbit/s per module, up to 4 modules on one PC card
1 light source1 beam splitter2 photon countersin a few cm3
(4x5x1 cm3) !!!
www. idquantique.com
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Few « qubit » ApplicationsPhoton-counting OTDR
Coherent Q measurement of the degree of polarization:
0 20 40 60 80 100 120
0.00.10.20.30.40.50.60.70.80.91.0
symbole plein: polarimètre symbole vide: projection sur (-)
DOP=1 DOP=0.74 DOP=0.34
DO
P
temps(s)
J.Lightwave Tech, 2, 390, 2004
PRL 91, 167902, 2003
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Conclusions
Where are the applications?
Next September 29, id Quantique, DeskPoint and the University of Geneva will officially inaugurate the
first data archive site secured with Quantum Cryptography.
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Single Photon Sources
919 nm / 0.7 nm
650 nm/ >50 nm
1550 nm / 7nm
/
Quantum Dot
NVHigh pump
Low pump
271.40.12g(2)(0) [%]
0.040.0020.30.02P2 [%]
8.32.26060P1 [%]
76 MHz5.3 MHz803 kHz34 kHzNT
Beveratos et. al., PRL 89, 187901 (2002)Vuckovic et. al., APL 82, 3596 (2003)
Fasel et. al. in preparation 21
2)2(
P
P2)0(g
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Size of the classical communication
One proton in one cm3 at a temperature of 300 K:
][017.12m
pkT 10
2
mp
h
233
019.1)dim(
L
Hd
155)(ln 22 d bits
1020 protons in one cm3 at a temperature of 300 K 1020 x 155 1022 bits
To be compared to today’s optical fiber communication in labs:
1 Tbyte x 1024 WDW channels x 1000 fibers 1019 bits/sec.
1 hour !!
bits
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entangled time-bin qubit
variable coupler
non-linearcrystal B
sA
sl
B
lA
AAi
BA 11e00
depending on coupling ratio and phase , maximally and non-maximally entangled states can be createdR. Thew et al, PRA 66, 062304, 2002
Extensions to entanglement in higher dimensions:- qutrits: R. Thew et al, quant-ph/0307122- up to dimesnion 20: H. Deriedmatten et al, quant-ph/0309058 5 10 15 20
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Vis
ibil
ity
Dimension d
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Bell state measurementBell state measurement
BABABBAAii 0110101010
21
BABABBAAii 0110101001
21
)1010(01102121 BBAA
i BABA
011001102121
H. Weinfurter, Europhysics Letters 25, 559-564 (1994)H. de Riedmatten et al., Phys. Rev. A 67, 022301 (2003)
1 2
A B