ilja gerhardt, matthew p. peloso, caleb ho, antía lamas ... · • freespace: ad-hoc set-up ilja...
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QUANTUM OPTICSCQT
GROUPQUANTUM OPTICSQUANTUM OPTICSCQTCQT
GROUPGROUP
Centre forQuantumTechnologies Singapore GROUPGROUPTechnologies, Singapore
Entanglement based Free Space Entanglement-based Free Space Quantum Cryptography in Full Daylight
Ilja Gerhardt
Ilja Gerhardt, Matthew P. Peloso, Caleb Ho, Antía Lamas-Linares and Christian Kurtsiefer
Ph i D t t NUSPhysics Department, NUSQuantum Optics Group• Single atom light interaction
IThH3, g g
• Single quantum emitters• Multiphoton entanglement• Experimental Tests of non Locality
JWA103
Ilja Gerhardt
• Experimental Tests of non-Locality• Quantum Key Distribution
QUANTUM OPTICSCQT
GROUPIntroduction to QKDIntroduction to QKD
• Quantum Cryptography =Quantum Cryptography Quantum Key Distribution–Have a Random Number at two locations
One-time pad for encryptionp yp
• 1980ies: Prepare and Send1980ies: Prepare and Send–Bennet Brassard, BB84–Send single Photons, non-cloning theorem
• 1990ies: Entanglement Based… why?
Ilja Gerhardt
g y
QUANTUM OPTICSCQT
GROUPPrepare and SendPrepare and Send
• Need for Random NumbersNeed for Random Numbers
• Different Photons, different Colors?–Dimensionality of Hilbert space needs to be
known for security
Ilja Gerhardt
QUANTUM OPTICSCQT
GROUPEntanglement based QKDEntanglement based QKD
• Ekert 1991 (E91)Ekert 1991 (E91)–Let’s measure two qubits of an entangled entity
P f (A i) l i– Perfect (Anti)correlation–Bell’s inequality violated= eavesdropper knowledge can be eliminated via PA
• Photons for convenience…• Freespace: Ad-hoc set-up
Ilja Gerhardt
QUANTUM OPTICSCQT
GROUPEntanglement based QKDEntanglement based QKD
• Pairsource: BBO, lean & compactPairsource: BBO, lean & compact–Strong temporally correlated ☺
B d h di d l –Broader than dimmed lasers
Ilja Gerhardt
19’’10’’
QUANTUM OPTICSCQT
GROUPDetection of PhotonsDetection of Photons
• Detection: Polarization analyzer
50 50PBS
λ/222.5°
Detection: Polarization analyzer
50:50 APD, +45°
22.5
PBS V
Ilja Gerhardt
-45°HJ.G. Rarity et al., J. Mod. Opt. 41, 2345 (1994)
QUANTUM OPTICSCQT
GROUPSetupSetup
BobAlice
telescopeSending
telescopeReceiving350 m
HWBS PBS
CC
WP
PBS
PA
BBO
Rb TURbTU 350 m
PCPCClassical Channel
Ilja Gerhardt M. Peloso et al., New J. Phys. 11 045007 (2009)
QUANTUM OPTICSCQT
GROUPProblems in DaylightProblems in Daylight
• Destruction of detectorsDestruction of detectors• Non-linearity of the detector
s]–Saturation
1.0
1.5
2.0
2.5
ed C
ount
s [1
0cp
s6
• Accidental clicks 0 2 4 6 8 100.0
0.5
Ideal Counts [10 cps]6
Det
ecte
–Confused with real coincidence events (QBER)
• Fl t ti f 30dB (d / i ht)Ilja Gerhardt
• Fluctuations of ~30dB (day/night)M. Peloso et al., New J. Phys. 11 045007 (2009)
QUANTUM OPTICSCQT
GROUPExpected Rates at daylightExpected Rates at daylight
Ilja Gerhardt M. Peloso et al., New J. Phys. 11 045007 (2009)
QUANTUM OPTICSCQT
GROUPSun & SolutionsSun & Solutions
sun
interferencefilter
sun
6focusing focusing filter 6.7nm
blackout shield bafflespinhole
to detectors
coatingbaffles
- 3-4 dB-12 dB100µradµFOV=10cm
Δt=1ns
Ilja Gerhardt M. Peloso et al., New J. Phys. 11 045007 (2009)
QUANTUM OPTICSCQT
GROUPSetupSetup
Alice
B bIlja Gerhardt
BobM. Peloso et al., New J. Phys. 11 045007 (2009)
QUANTUM OPTICSCQT
GROUPMeasured rates at daylightMeasured rates at daylight
Ilja Gerhardt M. Peloso et al., New J. Phys. 11 045007 (2009)
• Sync possible at daylight
QUANTUM OPTICSCQT
GROUPExperimental resultsExperimental results
total detection rate total 'local' detectorat receiver (kcps)
total local detectorrate at source (kcps)
coincidences(cps)
raw key rate(s-1) key rate afterkey rate after
error correction (s-1)
accidentalcoincidencerate r (cps)
QBER (%)
Ilja Gerhardt
rate ra (cps)
M. Peloso et al., New J. Phys. 11 045007 (2009)
QUANTUM OPTICSCQT
GROUPConclusionsConclusions
• Entanglement based QKD in daylight,Entanglement based QKD in daylight,4 days run without interruptionS h i i k bi • Synchronization works at ambient conditions
• Noise Suppression– SpectralSpectral– Temporal
Spatial– Spatial
• Brighter Sources…70 pairs/(s mW MHz)
Ilja Gerhardt M. Peloso et al., New J. Phys. 11 045007 (2009)
QUANTUM OPTICSCQT
GROUPThanks for your attentionThanks for your attentionThanks for your attentionThanks for your attention
Interested in Single Molecules?
Ilja Gerhardthttp://qolah.orghttp://qolah.org
Single Molecules?IThH1, Thursday, 2:30pm, Room 315
QUANTUM OPTICSCQT
GROUP
Ilja Gerhardt
QUANTUM OPTICSCQT
GROUPRates in DaylightRates in Daylight
• Sifting / Signal rate:Sifting / Signal rate:
• Accidentals:
Ilja Gerhardt
QUANTUM OPTICSCQT
GROUPSetupSetup
BobAlice
telescopeSending
telescopeReceiving350 m
HWBS PBSPH
CCWP
IF
PBSShields
Baffles
PA
BBO
Rb TURbTU 350 m
PCPCClassical Channel
Ilja Gerhardt
QUANTUM OPTICSCQT
GROUPCoincidence CountingCoincidence Counting
600
700 coincidencewindow±45°
H/V
a.u.
]
400
500
even
ts [
a
300
400
100
200
? [ ]
0-3 -2 -1 0 1 2 3
Ilja Gerhardt
? t [ns]
QUANTUM OPTICSCQT
GROUPSpectral filteringSpectral filtering
1 1λ0 = 813 1 nmλ0 = 811 4 nm
0.8
1
0.8
1on
[%
]
m [
a.u.
]
λ0 = 813.1 nm
ΔλFWHM = 8.7 nm
λ0 = 811.4 nm
ΔλFWHM = 6.7 nm
0.6 0.6
nsm
issi
o
pect
rum
0.4 0.4
ilter
tra
n
ourc
e sp
0.2 0.2
fi so
0 795 800 805 810 815 820 825 830
0
Wavelength [nm]
Ilja Gerhardt
g [ ]
QUANTUM OPTICSCQT
GROUPDead timeDead time
detectionevent
time [ s]µtime [ s]µ
Ilja Gerhardt
QUANTUM OPTICSCQT
GROUPCorrelation MatrixCorrelation Matrix
H 45° V 45°
Daylight Correlation
599 22791 34032 18409H
H -45° V +45°
18647 2894 17512 4484145° 18647 2894 17512 44841-45
29062 16422 2125 25246V
14635 40558 22280 1498+45°
Ilja Gerhardt
QUANTUM OPTICSCQT
GROUPEntanglement Based QKDEntanglement Based QKD
• Source of entanglement (BBO-Crystal)Source of entanglement (BBO Crystal)
Time Alice BobTime Alice Bob
19:35:01:… H V
19 35 01 45 +4519:35:01:… -45 +45
19:35:01:… V H
19:35:01:… V H
19:35:01:… -45 +45
19:35:01:…
Ilja Gerhardt