Non-Classical State Generation and Quantum Memories for Light(III)

Lecture 3• Introduction to quantummemories for light and scalable QIT• How ? Single-atom and ensemblebasedquantum memoriesEnsemble-based techniques• Duan-Lukin-Cirac-Zoller approach• Dynamic EIT memories• Photon-echo techniques

Quantum Memories for LightPhotonic QubitDesideratum : Storing a quantum statewithout measuring it and reading on demand,i.e. a coherent and reversible transferbetween atoms and light.writereadQ.Memory

Quantum Memories for LightPhotonic QubitDesideratum : Storing a quantum statewithout measuring it and reading on demand,i.e. a coherent and reversible transferbetween atoms and light.writereadQ.MemorySome important propertieswriteQ. Memory read• Storage time• Efficiency• Fidelity (conditional or not)p write• Bandwidth, wavelength, mutimode storage…p read

One example : Quantum Repeaters1) Divide into segments andgenerate entanglementL 0L 0 L 0. .. .. .L. .. .. .. .. .F

Towards a Single Atom MemoryOne atom in a high finessecavity (strong coupling)First demonstration of areversible mapping

A Single Atom Quantum MemoryOne atom in a high finessecavity (strong coupling)Storage and read-out of aweak coherent pulse witharbitrary polarization stateNature, may 2011~9%

Lecture 3• Introduction to quantummemories for light and scalable QIT• How ? Single-atom and ensemblebasedquantum memoriesEnsemble-based techniques• Duan-Lukin-Cirac-Zoller approach• Dynamic EIT memories• Photon-echo techniques

The DLCZ Paradigm (2001)

Creating a Single Collective ExcitationNonclassical correlations between field 1 and the ensembleWriteField 1: the excitation probabilityWriteField 1Collective atomic state

Retrieving the Single ExcitationField 2ReadField 2WriteField 1ReadCollective enhancement if :Atoms at rest :Moving atoms:

Retrieving the Single ExcitationField 2ReadField 2WriteField 1ReadCollective enhancement if :Atoms at rest :Moving atoms:A good source of heralded single-photons!• Retrieval in a single mode fiber ~ 50 %• Suppression of two-photon component : 1%J. Laurat et al., Opt. Express 14, 6912(2006)

Entanglement between Two EnsemblesHeralded entanglementbetween remote memories,induced by a measurement.First experimentaldemonstration in 2005Nature 438, 828 (2005)Goal - generate the entangled state:One collective excitation “delocalized”between the two ensemblesSuccessful demonstration for memoriesseparated by 3 metersScheme from the DLCZ paper

Entanglement between Two EnsemblesAtomsentangledLight50/50Beam splitterLightAtomsentangled

Entanglement between Two Ensembles1 photon detected 1 atom transferred50/50Beam splitter

Entanglement between Two Ensembles1 photon detected 1 atom transferredLhereEntangledGeneral (and ideal) casethereRwhere =here+there

• 2 memoriesseparated by 3m• 1 collective excitationshared in an entangled statebetween the two ensemblesC.W. Chou et al., Measurement-induced entanglement for excitation stored in remote atomic ensembles, Nature 438, 828 (2005)

Entanglement between Two EnsemblesHeralded entanglementwith ‘large’ concurrenceand study of the temporaldynamics1 success over 1000 tries(160 Hz preparation rate)Concurrence (0

A Quantum Repeater SegmentA rudimentary repeater segmentAll the ingredients : parallel pairs,asynchronous preparation, Bellviolation…Science 316, 1319 (2007)

• 2 nodes separated by 3m• 2 ensembles per node• Asynchronous preparation(memory) of 2 parallelnumber-state entangled pairs• Polarization coding andpassive phase stabilityPolarization entanglementdistribution, violating BellC.W. Chou, J. Laurat, H. Deng, K.S. Choi, H. de Riematten, D. Felinto, H.J. Kimble, FunctionalQuantum Nodes for Entanglement Distribution over Scalable Quantum Networks, Science 316, 1316 (2007)

DLCZ-based Exeriments : ProgressNature Phys. 3, 765 (2007)Ensemble inside a cavity : readout>80%Nature 454, 1098 (2008)Another example of elementary repeater segment

DLCZ-based Exeriments : ProgressMemory time in the ms range…In the 0.1s range…Single-photon storage

Lecture 3• Introduction to quantummemories for light and scalable QIT• How ? Single-atom and ensemblebasedquantum memoriesEnsemble-based techniques• Duan-Lukin-Cirac-Zoller approach• Dynamic EIT memories• Photon-echo techniques

Electromagnetically-Induced Transparencysignal (0)cStrongabsorption atresonanceQuantum interference effects in theamplitudes of optical transitions in atomicmedium can lead to strong modifications ofits optical properties.c0From Nature 438, 833 (2005)

Electromagnetically-Induced TransparencyQuantum interference effects in theamplitudes of optical transitions in atomicmedium can lead to strong modifications ofits optical properties.signal (0)ccLeads to ‘Slow light’(Reduction of thegroup velocity)0Kramers-Kronig relations : anomaly inabsorption spectrum is accompaniedby anomaly in the dispersionFrom Nature 438, 833 (2005)

Dynamic EIT based MemoryWhen the pulse has been spatiallycompressed into the medium, thecontrol field is adiabaticallyswitched off.The quantum state of light is inthis way transferred to the atomiccoherence between the twoground states.Later, on demand, by switching onagain the control field, thecoherence is mapped back topropagating light field.

EIT Storage and Retrieval of Single-PhotonsNature 438, 837 (2005)Nature 438, 833 (2005)

Mapping Entanglement Into and OutIdea

Mapping of Single Photon EntanglementNature 452, 67 (2008)C out /C in : 20% entanglement transfertLet’s see more in details this experiment in the next slides…

Mapping Entanglement Into and OutAtomic Ensemblesas heralded singlephoton source for proofinprinciple demonstration

• An heralded single photonsource ( =0.09 ± 0.03)• One entangler (well, a BS)10 + 012• Mapping by dynamical EIT• 20% Entanglement transfertDecouple entanglementand preparation rateK. S. Choi, H. Deng, J. Laurat and H. J. Kimble., Mapping photonic entanglement intoand out of a quantum memory, Nature 452, 67 (March 2008)

The Real Story

EIT Storage in the CV Regime

Lecture 3• Introduction to quantummemories for light and scalable QIT• How ? Single-atom and ensemblebasedquantum memoriesEnsemble-based techniques• Duan-Lukin-Cirac-Zoller approach• Dynamic EIT memories• Photon-echo techniques

Rare-earth ions doped intoinorganic crystals.Ex.: Thulium, PraseodymiumSolid State Atomic Ensembles

Rare-earth ions doped intoinorganic crystals.Ex.: Thulium, PraseodymiumSolid State Atomic EnsemblesWhy they look interesting?- Large number of atoms. Notrapping needed- Non-moving atoms : echocan be efficientlyimplemented- Excellent coherenceproperties at cryogenictemperature (T

General Idea : Photon-Echo TechniquesInhomogeneous dephasingCollective state :Very fast decay of the alignement of the atomic dipolesNeeds a controlled rephasing process

General Idea : Photon-Echo TechniquesInhomogeneous dephasingCollective state :Very fast decay of the alignement of the atomic dipolesNeeds a controlled rephasing process2-pulse photon echo In the Bloch sphere :Illustrations from W. Tittel et al., Laser Photonics Review 4, 244 (2009)Rephasing at a certain time of all the dipoles triggersthe re-emission of the absorbed signal

General Idea : Photon-Echo TechniquesInhomogeneous dephasingCollective state :2-pulse photon echo In the Bloch sphereNot a:good QM strategy…- Strong optical pulse in thequantum channelIllustrations from W. Tittel et al., Laser Photonics Review 4, 244 (2009)Very fast decay of the alignement of the atomic dipolesNeeds a controlled rephasing process- Contamination of the singlephotonecho by unavoidablefluorescenceRephasing at a certain How time to of avoid all these dipoles triggersthe re-emission contaminations of the absorbed ? signal2 ways : CRIB and AFC

Controlled Reversible Inhomogenous BroadeningCRIBIllustrations from W. Tittel et al.,Laser Photonics Review 4, 244 (2009)

Controlled Reversible Inhomogenous BroadeningNature 465, 1052 (2010)=69%

Atomic Frequency Comb (AFC)• Collective state at t=0• After a time t (dephasing)• Rephasing after a time

Atomic Frequency Comb (AFC)For long-livedstorage• Collective state at t=0• After a time t (dephasing)• Rephasing after a time

Atomic Frequency Comb (AFC)For long-livedstorageSome advantages relative to CRIB:- Better use of the optical depth (OD)- Multimode capacity (only limited by the broadeningwhile in CRIB number of modes scales with OD and in EIT it scales withFor instance : 1060 modes : M. Bonarota et al., Highly multimode storage in a crystal, NJP 13, 013013 (2010)OD)

Atomic Frequency Comb (AFC)Bell violation S=2.65>2See other works in Orsay (Chanelière/Le Gouet), Lund (Kroll),…

Summary• Optical quanutm Memories forscalable QIT. .• Single-atom vs ensemble-basedCollective enhancement• DLCZ approach• EIT-based memories• Photon-echo techniques

Some ReviewsQuantum interface between light andatomic ensemblesK. Hammerer et al., Rev. Mod. Phys. 82,1041 (2010)Optical quantum memoriesA.I. Lvovsky et al., Nature Photon. 3, 706(2009)Quantum repeaters based on atomicensembles and linear opticsN. Sangouard et al., Rev. Mod. Phys. 83,33 (2011)Photon-echo quantum memory insolid state systemsW. Tittel et al., Laser Photonics Review 4,244 (2009)

Some ReviewsQuantum interface between light andatomic ensemblesK. Hammerer et al., Rev. Mod. Phys. 82,1041 (2010)Optical quantum memoriesA.I. Lvovsky et al., Nature Photon. 3, 706(2009)Quantum repeaters based on atomicensembles and linear opticsN. Sangouard et al., Rev. Mod. Phys. 83,33 (2011)Open Postdoc positions inexperimental quantumoptics and quantuminformation-Q. Memory- Q. State EngineeringFeel free to contact me!Photon-echo quantum memory insolid state systemsW. Tittel et al., Laser Photonics Review 4,244 (2009)