1 GAP Optique Geneva University 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
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. Quantum Communication. Nicolas Gisin Hugo Zbinden, Ivan Marcikic, Hugues de Riedmatten, - PowerPoint PPT Presentation
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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)
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
Yesterday, September 29, id Quantique, DeckPoint and the University of Geneva officially inaugurated the first data archive site secured with Quantum Cryptography.
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)