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- Quantum Storage of Photonic Entanglement in Nd:Y2SiO5
- Towards a complete AFC quantum memory in Eu:Y2SiO5
Imam Usmani, Christoph Clausen, Félix Bussières, Björn Lauritzen, Nuala Timoney,Mikael Afzelius, Hugues de Riedmatten, Nicolas Sangouard, Nicolas Gisin
Group of Applied Physics, University of Geneva - Switzerland
Coherent and reversible mapping of entanglement between photons (flying qubits) and atoms (stationary qubits)
Enables entanglement of remote material systems A resource for future quantum repeaters/quantum networks Solid-state resources could provide a scalable and affordable
solution
Light-matter interfaces Light-matter interfaces For Quantum NetworksFor Quantum Networks
QuantumChannel
QuantumChannel
QuantumNode
QuantumNode
Genève
Bern
Zurich
Photon
Emissive quantum memory
‣Single atoms/ions: Blinov et al, Nature 428, 153 (2004) Volz et al, PRL 96, 030404 (2006) H. P. Specht, doi:10.1038/nature09997‣NV centers: Togan et al, Nature 466, 730 (2010)‣Atomic ensembles (DLCZ): Matsukevich et al, PRL 95, 040405 (2005) de Riedmatten et al, PRL 97, 113603 (2006)
Continous variables quantum memory
J. Sherson et al., Nature 443, 557 (2006)
SPDC + quantum memory‣Single ions: Piro et. al., Nature Phys. 7, 17-20 (2011)
‣Atomic ensembles: Jin et al, arXiv:1004.4691 (2010)
+ No atom trapping+ One telecom photon
Light-matter entanglementLight-matter entanglementin quantum information sciencein quantum information science
k
Building a Quantum Memory withBuilding a Quantum Memory withan Atomic Ensemblean Atomic Ensemble
Collective interference Collective enhancement factor N
kNj ggg 1......1 Before absorption
kNj ggg 1......1 After re-emission
All atoms in ground state 1 photon in optical mode k
N
jNj
ikr gegeN
j
11 ......
1After absorption Huge superposition state!
Macroscopic numberN=108-1010
Spatial phase imprinted onto the atomic ensemble
g
e
K. Hammerer, A.S. Sorensen, E.S. Polzik, RMP 82, 1041 (2010)A. I. Lvovsky, B. C. Sanders, W. Tittel, Nature Photonics 3, 706 (2009)
Properties of RE-doped crystalsProperties of RE-doped crystals
Weak interaction with crystal enviroment - "atom" like energy structure for 4f-4f transitions - "frozen gas" of ions, no motional decoherence
High number of stationary ions (107-1010) - strong light-matter coupling
Long optical coherence times (T < 4K), T2opt = 1 s – 1 ms (h = 300 kHz – 300 Hz)
Long hyperfine coherence times (T < 4K), T2hyp = 1 ms – 1 s
Large inhomogeneous broadenings 100 MHz – 10 GHz
Quantum Memory in an Rare-earth EnsembleQuantum Memory in an Rare-earth Ensemble
(nm) = 606 880 580 1550 790
REVIEW: W. Tittel, M. Afzelius, T. Chanelière, R. L. Cone, S. Kröll, S. A. Moiseev, and M. Sellars, Laser & Photon. Rev., 1 (2009)
Y2SiO5 CrystalLow Nuclear Spin Density
Inhomogeneous ensemble (eg. RE-crystals)
Ab
sorp
tion
Frequency
GHz
Non-directional, spontaneous re-emission at random time
dephasing!
How to rephase the coherence?
Quantum Memory in an Rare-earth EnsembleQuantum Memory in an Rare-earth Ensemble
(nm) = 606 880 580 1550 790
AFC preparation
Photon
Signal
Time
Preparation
Photon Echo
Echo
Control
Echo
2 levels: preprogrammed delay (AFC echo)3 levels: on-demand re-emission (spin wave storage)
M. Afzelius et al. PRA 79, 052329 (2009)
Periodic!
Atomic Frequency Comb (AFC) Quantum MemoryAtomic Frequency Comb (AFC) Quantum Memory
Multimode !
Multimode !
-2 0 2 4 6 80
200
400
600
800
1000
Detector noise
Co
un
ts [
/20
0s]
Phase [rad]
Nature 456, 773 (2008)
Nature Comm. 1, 12, 2010
Recent AFC/CRIB progress at UNIGERecent AFC/CRIB progress at UNIGE
TelecomMemory
Entanglement source :Photon pair source by SpontaneousParametric down Conversion (SPDC)
A light matter interface :Quantum Memory in a Nd3+ dopedcrystal
Entanglement measurement :Energy-time entanglementFranson experiment
This experiment: Light-Matter EntanglementThis experiment: Light-Matter Entanglement
IngredientsIngredients::
45 MHz
1.5 THz
Storing a single photon generated by SPDC : technical challenges
‣Strong filtering to match the 100 MHz bandwidth of our quantum memory : from 1.5 THz to 45 MHz!
‣Lock pump’s wavelength to satisfy energy conservation
A Narrowband SPDC source ofA Narrowband SPDC source ofEnergy-time entangled photonsEnergy-time entangled photons
~ 6 GHz
~100 MHz
A bit more complicated in reality…A bit more complicated in reality…
&
Cry
stal
Col
d fi
nge
r 3
K
Frequency
Storage of a heralded photon in NdStorage of a heralded photon in Nd3+3+:Y:Y22SiOSiO55
Experimental comb
Optimal AFC efficiency using square peaks
M. Bonarota et al., Phys. Rev. A 81, 033803 (2010)
Signal-Idler cross-correlation vs. storage timeSignal-Idler cross-correlation vs. storage time
C. Clausen, I.Usmani, F. Bussières, M Afzelius, N. Sangouard, H. de Riedmatten and N. Gisin, Nature 469, 508 (2011)
Energy-time entanglement :
•Photons created simultaneously
within c
•Creation is uncertain (in a quantum sense) to within the coherence time of
pump p
Thus their creation time are entangled!
Energy-time entanglement from a SPDC sourceEnergy-time entanglement from a SPDC source
CW PUMPEDSPDC SOURCE
fiberinterferomet
er
Franson interferometer
Energy-time entanglement :
•Photons created simultaneously
within c
•Creation is uncertain (in a quantum sense) to within the coherence time of
pump p
Thus their creation time are entangled!
Interferenceshort-shortlong-long
Interferenceshort-shortlong-long
Energy-time entanglement from a SPDC sourceEnergy-time entanglement from a SPDC source
C. Clausen, I.Usmani, F. Bussières, M Afzelius, N. Sangouard, H. de Riedmatten and N. Gisin, Nature 469, 508 (2011)
Alice’s analyser(fibered interferometer)
Entanglement verification by violation of Bell inequality
Bob’s analyser("interferometer" in the crystal)
CrystalQuantum Memory
Light-matter entanglementLight-matter entanglement
Bob’s measurement choice (phase)
C. Clausen, I.Usmani, F. Bussières, M Afzelius, N. Sangouard, H. de Riedmatten and N. Gisin, Nature 469, 508 (2011)
Entanglement verification by violation of Bell inequality
Coincidences in central peak
limit) (local 223.064.2 S),(),(),(),( 22211211 YXEYXEYXEYXES
Violation of Bell-CHSH inequality
Witness oflight-matter entanglement
Light-matter entanglementLight-matter entanglement
Similar experiment by the group of Wolfgang Tittel (U. of Calgary)
E. Saglamyurek, N. Sinclair, J. Jin, J. A. Slater, D. Oblak, F. Bussières, M. George, R. Ricken, W. Sohler & W. Tittel. Nature 469, 512 (2011).
Tm3+:LiNbO3 Waveguide - 5 GHz - 7
ns storage
Light-matter entanglementLight-matter entanglement
OUTLOOKOUTLOOKEntangling excitation stored in two crystalsEntangling excitation stored in two crystals
Singlephoton
Singlephoton
Heralded entangled state of two crystal QMs
Mem
ory
AM
emory
AMemory
BMemory
B
PREVIOUS WORK:K. S. Choi, H. Deng, J. Laurat & H. J. Kimble, Nature 452, 67 (2008)
J. Laurat, K. S. Choi, H. Deng, C. W. Chou, and H. J. Kimble, Phys. Rev. Lett. 99, 180504 (2007)
CONCLUSIONS NEODYMIUM PARTCONCLUSIONS NEODYMIUM PART• Development of frequency stabilized narrowband SPDC source
• Storage of a heralded single photon in Nd:Y2SiO5 crystal
• Demonstration of entanglement between a telecom photon and a stored excitation
Quantum Communication (QC)Quantum Communication (QC)
Alice BobPhotonsource
qubi
t
10 10 iecc
Genève
Neuchâtel High-speed Quantum Cryptography Field Experiment
Fiber length: L ~150kmLosses: 43 dB (0.29dB/km)
Base Freq: >300 Mbits/s
Secret bit key rate: 2.5 bits/s(average value over 3 h !)
Damien Stucki et al., arXiv:0809.5264
1 click
Initial state
Pump
MemoryMemory
SPDC source A
SPDCsource B
A more concrete example!!A more concrete example!!
Conditional state (one click!)
Heralded entangled state of remote QM
Long-distance QC - Quantum RepeaterA Z
The average time to establish entanglement between A and Z is polynomial in the time to create the entanglement in one link, eg. AB.
H.J. Briegel W.Dur, J.I. Cirac, P.Zoller, PRL 81, 5932 (1998)L.M. Duan, M.D. Lukin, J.I. Cirac, P.Zoller, Nature 414, 413 (2001)
Requires heralded creation, storage and swapping of entanglement.
AB
B
Entanglement swapping
CCD
D
A DAD
A ZAZ
Create entanglement independently for each link. Extend by swapping.
Ensemble based Quantum MemoryEnsemble based Quantum Memory
Quantum Physical system:
Must preserve the quantum state of the
photon
Quantum memory
Typically: Coherent atoms
Two important properties:- Efficiency
- Conditional fidelity
READWRITE pp
inoutinF F=1 means an output photon with the same state as the input photon
WRITE
WRITEp
in
The goal of the quantum memory is to temporarily store the quantum state of a photonin
outREAD
READp
e
g
Ato
mic
den
sity
Atomic detuning
Out
put m
ode
Inpu
t mod
e
N
kNkk geggc
121 ......
State after absorption
Atomic Frequency Comb (AFC) Quantum MemoryEnsemble of inhomogeneously broadened atomsIn
tens
ity
Time
Inputmode
Outputmode
Control fields
0/2 T 0TsT
s
Control fields
Storage state
N
kNk
tik geggec k
121 ......
Dephasing
kk m
Periodic structure =>Rephasing after a time
2et
Collective emission in the forward mode. Photon echo
like emission
Inte
nsity
Time
Inputmode
Outputmode
/2
(superradiant Dicke state)
M. Afzelius, C. Simon, H. de Riedmatten and N. Gisin, Phys Rev A 79, 052329 (2009)
0 10 20 30 40 500
10
20
30
40
50
60
70
80
90
100
Analytical Simulations
F = 10
F = 6
F = 4
Effic
ienc
y (%
)
Peak absorption d
2
72)1( FF
d
ee
Atomic detuning
FFinessed
Efficiency vs optical depth (theory)Efficiency vs optical depth (theory)
M. Afzelius et al. PRA 79, 052329 (2009)
0 5 10 15 20 25 30 35 40
100
1000
10000
CRIB
EIT
Opt
ical
dep
th
Number of temporal modes
Efficient Storage of multiple temporal modes
2pT
N pulses, total duration Tp
QM
Ato
mic
den
sity
Atomic detuning
p
peaksp N
11peaks
p
p NT
N
Number of modes limited by minimal and maximal
Does not depend on dAFC
Inpu
t mod
e
Out
put m
ode
Con
trol
fiel
ds
1/2
3/2
5/2
1/2
3/2
5/2
10.2 MHz
606
nm
3H4
1D2
AFC storage experiment in Pr3+:Y2SiO5
0 2 4 6 8 10 120
2
4
6
8
10
12
14
(b)
Nor
ma
lzie
d in
tens
ity (
arb
. un
its)
Time (s)
8 9 10 11 12 13
0.00
0.25
0.50 Output
M. Afzelius et al (2009)
Up to 20 microseconds storage timeLonger possible using spin echo control (up to 1 seconds)!
Stabilized ring dye-laser at 606 nm with 1-kHz bandwidth
Optical cryostat withPr:Y2SiO5 crystal
Multi-mode storage in Nd3+:Y2SiO5
0.0 0.2 0.4 0.6 0.8 1.00.000
0.025
0.050
0.075
0.100
0.0 0.5 1.0 1.5 2.0 2.50
1
2
3
4
5
6
eff
icie
ncy
[%
]
storage time [s]
N
orm
aliz
ed c
ount
s
Time [s]
Transmitted photons
Emitted photons
Storage efficiency as a function of storage time (one mode)
Weak coherent input statesn < 1
Multi-mode storage in Nd3+:Y2SiO5
0.0 0.4 0.8 1.2 1.6 2.0 2.40.0
0.2
0.4
0.6
0.8
1.0 Output modes x50
Nor
mal
ized
cou
nts
Time (s)
Input modes
Mapping 64 input modes onto one crystal
0.0 0.5 1.0 1.5 2.0 2.50.0
0.2
0.4
0.6
0.8
1.0
nor
ma
lize
d co
unts
time [s]
Input mode Output mode x50
0.0 0.5 1.0 1.5 2.0 2.50.0
0.2
0.4
0.6
0.8
1.0
norm
aliz
ed c
ount
s
time [s]
Input mode Output mode x50
n < 1 per mode
64 time modes can be used to code 32 time-bin qubits!Largest qubit memory achieved so far.
Multi-mode storage in Nd3+:Y2SiO5
Multimode (11 modes) interference experiment to check coherence!
0 200 400 600 800 1000 12000
20
40
60
80
100
120
140
Co
un
ts
Time [ns]
Consecutive modes are interfering with a different phase difference:
Numerical example of efficient multi-mode storage in Eu3+:Y2SiO5
Optical transition at 580 nmOptical homogenenous linewidth = 122 HzSpin coherence time = 36 msOptical depth d = 4 cm-1
Eu3+:Y2SiO5 properties:
AFC numerical simulation: Peak width = 2 kHzPeak separation = 20 kHzFinesse = 10Total AFC bandwidth = 12 MHzd=40
Efficient (90%) storage of 100 modes in ONE memory (30 shown below)
Cavity-enhanced Quantum Memory
The idea…. Takes a 1% efficient QM to >90%