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

- Quantum Storage of Photonic Entanglement in Nd:Y 2 SiO 5 - Towards a complete AFC quantum memory in Eu:Y 2 SiO 5. Imam Usmani, Christoph Clausen, Félix Bussières, Björn Lauritzen, Nuala Timoney, Mikael Afzelius, Hugues de Riedmatten, Nicolas Sangouard, Nicolas Gisin

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

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  1. - 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

  2. 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 For Quantum Networks Zurich Quantum Channel Bern Quantum Node Genève

  3. Photon Light-matter entanglement in quantum information science • 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

  4. Before absorption After re-emission After absorption All atoms in ground state 1 photon in optical mode k Spatial phase imprinted onto the atomic ensemble Building a Quantum Memory with an Atomic Ensemble Huge superposition state! Macroscopic number N=108-1010 Collective interference  Collective enhancement factor N 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)

  5. Quantum Memory in an Rare-earth Ensemble Absorption Frequency Properties 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 ms – 1 ms (Gh = 300 kHz – 300 Hz) • Long hyperfine coherence times (T < 4K), T2hyp = 1 ms – 1 s • Large inhomogeneous broadenings 100 MHz – 10 GHz GHz Self-rephasing using spectral tailoring? dephasing! Inhomogeneous ensemble (eg. RE-crystals) Non-directional, spontaneous re-emission at random time l (nm) = 606 880 580 1550 790 Y2SiO5 Crystal Low Nuclear Spin Density REVIEW: W. Tittel, M. Afzelius, T. Chanelière, R. L. Cone, S. Kröll, S. A. Moiseev, and M. Sellars, Laser & Photon. Rev., 1 (2009)

  6. Quantum Memory in an Rare-earth Ensemble Absorption Frequency GHz How to rephase the coherence? dephasing! l (nm) = 606 880 580 1550 790 Inhomogeneous ensemble (eg. RE-crystals) Non-directional, spontaneous re-emission at random time

  7. Atomic Frequency Comb (AFC) Quantum Memory Periodic! AFC preparation 2 levels: preprogrammed delay (AFC echo) Photon Control Echo 3 levels: on-demand re-emission (spin wave storage) Signal Preparation Multimode ! Echo Photon Echo Time M. Afzelius et al. PRA 79, 052329 (2009)

  8. Recent AFC/CRIB progress at UNIGE 1000 800 600 Counts [/200s] 400 Detector noise 200 0 -2 0 2 4 6 8 Phase [rad] Nature456, 773 (2008) Telecom Memory Nature Comm. 1, 12, 2010

  9. A light matter interface : Quantum Memory in a Nd3+ doped crystal This experiment: Light-Matter Entanglement Ingredients: Entanglement source : Photon pair source by Spontaneous Parametric down Conversion (SPDC) Entanglement measurement : Energy-time entanglement Franson experiment

  10. 1.5 THz 45 MHz ~100 MHz ~ 6 GHz A Narrowband SPDC source of Energy-time entangled photons • 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

  11. A bit more complicated in reality… &

  12. Storage of a heralded photon in Nd3+:Y2SiO5 Experimental comb 1/D Optimal AFC efficiency using square peaks M. Bonarota et al., Phys. Rev. A 81, 033803 (2010) Cold finger 3 K Crystal Frequency

  13. Signal-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)

  14. Energy-time entanglement from a SPDC source CW PUMPED SPDC SOURCE • 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!

  15. Energy-time entanglement from a SPDC source fiberinterferometer 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! Interference short-short long-long

  16. Light-matter entanglement Alice’s analyser (fibered interferometer) Bob’s analyser ("interferometer" in the crystal) Entanglement verification by violation of Bell inequality Crystal Quantum Memory C. Clausen, I.Usmani, F. Bussières, M Afzelius, N. Sangouard, H. de Riedmatten and N. Gisin, Nature 469, 508 (2011)

  17. Light-matter entanglement Coincidences in central peak Violation of Bell-CHSH inequality Witness of light-matter entanglement Bob’s measurement choice (phase) Entanglement verification by violation of Bell inequality C. Clausen, I.Usmani, F. Bussières, M Afzelius, N. Sangouard, H. de Riedmatten and N. Gisin, Nature 469, 508 (2011)

  18. Light-matter entanglement Similar experiment by the group of Wolfgang Tittel (U. of Calgary) Tm3+:LiNbO3 Waveguide - 5 GHz - 7 ns storage 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).

  19. OUTLOOK Entangling excitation stored in two crystals Single photon Memory B Memory A Heralded entangled state of two crystal QMs 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)

  20. CONCLUSIONS 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

  21. qubit High-speed Quantum Cryptography Field Experiment Neuchâtel 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 !) Genève Damien Stucki et al., arXiv:0809.5264 Quantum Communication (QC) Alice Bob Photon source b a

  22. A more concrete example!! Pump Initial state Conditional state (one click!) Heralded entangled state of remote QM Memory Memory 1 click SPDC source A SPDC source B

  23. Long-distance QC - Quantum Repeater A D A Z A B C D Z Entanglement swapping Create entanglement independently for each link. Extend by swapping. 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.

  24. Ensemble based Quantum Memory WRITE READ • Two important properties: • Efficiency • Conditional fidelity F=1 means an output photon with the same state as the input photon The goal of the quantum memory is to temporarily store the quantum state of a photon Quantum memory Quantum Physical system: Must preserve the quantum state of the photon Typically: Coherent atoms

  25. State after absorption Control fields Output mode Input mode Dephasing Storage state D Periodic structure => Rephasing after a time Output mode Input mode AtomicFrequencyComb (AFC) Quantum Memory Input mode Output mode Intensity Control fields Intensity Time Time Collective emission in the forward mode. Photon echo like emission Ensemble of inhomogeneously broadened atoms (superradiant Dicke state) Atomic density Atomic detuning  M. Afzelius, C. Simon, H. de Riedmatten and N. Gisin,Phys Rev A 79, 052329 (2009)

  26. Efficiency vs optical depth (theory) Finesse D d g Atomic detuning  M. Afzelius et al. PRA 79, 052329 (2009)

  27. Atomic density Atomic detuning  D g Efficient Storage of multiple temporal modes N pulses, total duration Tp G QM tp • Number of modes limited • by minimal g and • maximal G AFC • Does not depend on d

  28. AFC storage experiment in Pr3+:Y2SiO5 5/2 1D2 3/2 1/2 606 nm Control fields Input mode Output mode 1/2 10.2 MHz 3/2 3H4 5/2 Output Up to 20 microseconds storage time Longer possible using spin echo control (up to 1 seconds)! M. Afzelius et al (2009)

  29. Stabilized ring dye-laser at 606 nm with 1-kHz bandwidth Optical cryostat with Pr:Y2SiO5 crystal

  30. Multi-mode storage in Nd3+:Y2SiO5 Storage efficiency as a function of storage time (one mode) Weak coherent input states n < 1

  31. Multi-mode storage in Nd3+:Y2SiO5 Mapping 64 input modes onto one crystal n < 1 per mode 64 time modes can be used to code 32 time-bin qubits! Largest qubit memory achieved so far.

  32. Multi-mode storage in Nd3+:Y2SiO5 Multimode (11 modes) interference experiment to check coherence! Consecutive modes are interfering with a different phase difference:

  33. Numerical example of efficient multi-mode storage in Eu3+:Y2SiO5 Eu3+:Y2SiO5 properties: Optical transition at 580 nm Optical homogenenous linewidth = 122 Hz Spin coherence time = 36 ms Optical depth d = 4 cm-1 AFC numerical simulation: Peak width = 2 kHz Peak separation = 20 kHz Finesse = 10 Total AFC bandwidth = 12 MHz d=40 Efficient (90%) storage of 100 modes in ONE memory (30 shown below)

  34. Cavity-enhanced Quantum Memory The idea…. Takes a 1% efficient QM to >90%

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