- Quantum Storage of Photonic Entanglement in Nd:Y 2 SiO 5 - Towards a complete AFC quantum memory...

- 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


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)


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


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


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


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.


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%

- Quantum Storage of Photonic Entanglement in Nd:Y 2 SiO 5 - Towards a complete AFC quantum memory...

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