Thesis defense

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Ph.D thesis defense presentation on the construction of a quantum memory for squeezed light

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Thesis defense

  1. 1. Towards a Quantum Memory for Non-Classical Light With Cold Atoms<br />Sidney Burks<br />October 13, 2010<br />Thesis Director: Elisabeth Giacobino<br />Thesis Co-director: JulienLaurat<br />Quantum Optics Group<br />Laboratoire Kastler-Brossel<br />Université Pierre et Marie Curie, Paris<br />1<br />
  2. 2. From Classical Bits to Quantum Bits<br />Classical information is based on the bit<br />Discrete values of 1 or 0<br />Photonic bits<br />Quantum information introduces the qubit<br />Superposition of states<br />2<br />
  3. 3. A Quantum Memory<br />Desideratum : Storage without measurement, on-demand retrieval<br /> i.e. a coherent and reversible transfer between light and matter. <br />General Strategy: Transfer the quantum superposition of light onto a superposition of states in a storage medium<br />Photonic qubit<br />3<br />
  4. 4. A Quantum Memory<br />Desideratum : Storage without measurement, on-demand retrieval<br /> i.e. a coherent and reversible transfer between light and matter. <br />General Strategy: Transfer the quantum superposition of light onto a superposition of states in a storage medium<br />The states |a> and |b> are typically ground states in order to avoid a rapid decoherence<br />General Recipe: Two ground states are connected via an excited state by a control field<br />Photonic qubit<br />4<br />
  5. 5. A review of Quantum Memories<br />Single Atom<br />Cavity Quantum Electrodynamics (strong coupling)<br />“Dynamic” EIT<br />Experiments at LKB<br />Atomic Ensemble: Collective Excitation<br />Rephasing protocols<br />- CRIB and AFC - <br />Rare earth elements in solids at cryogenic temperatures<br />Long lifetime<br />5<br />
  6. 6. Applications of Quantum Memories<br /><ul><li>Most photon sources are probabilistic
  7. 7. We know however, how to create twin photon sources</li></ul>6<br />
  8. 8. Applications of Quantum Memories<br /><ul><li>Most photon sources are probabilistic
  9. 9. We know however, how to create twin photon sources
  10. 10. Memory loaded with a photon</li></ul>7<br />
  11. 11. Applications of Quantum Memories<br />Deterministic “Photon Gun”<br />8<br />
  12. 12. Synchronization of photon emissions<br />Two-photon interference<br />9<br />
  13. 13. Synchronization of photon emissions<br />Two-photon interference<br />Quantum gates<br />10<br />
  14. 14. Quantum Networks<br />Distribution of entanglement throughout a network<br />Propagation of entanglement in complex quantum systems<br />Simulation of collective phenomenon<br />H.J. Kimble, The Quantum Internet, Nature 453, 1023 (2008)<br />11<br />
  15. 15. 12<br />Long-distance Quantum Communication<br />Quantum states are fragile<br />Impossible to clone arbitrary quantum states<br />Amplification impossible!<br />
  16. 16. Long-distance Quantum Communication<br />100 km, telecom fiber: 99.5 % losses<br />For 1000 km, and with a 10GHz qubit source, it would take 300000 years to transmit 1 qubit<br />Connection time increases exponentially with distance<br />13<br />
  17. 17. Long-distance Quantum Communication<br />100 km, telecom fiber: 99.5 % losses<br />For 1000 km, and with a 10GHz qubit source, it would take 300000 years to transmit 1 qubit<br />Connection time increases exponentially with distance<br />Quantum repeaters<br />14<br />
  18. 18. Divide into segments and Generate Entanglement<br />.<br />.<br />.<br />.<br />.<br />.<br />L0<br />L0<br />L0<br />L<br />.<br />.<br />.<br />.<br />.<br />.<br />2) Entanglement Swapping<br />.<br />.<br />.<br />.<br />Quantum repeaters<br />Fidelity is close to 1 at long distances, but… the time increases exponentially with distance<br />Entanglement of the segments is probabilistic: each step occurs at a different moment.<br />15<br />
  19. 19. Divide into segments and Generate Entanglement<br />.<br />.<br />.<br />.<br />.<br />.<br />L0<br />L0<br />L0<br />L<br />.<br />.<br />.<br />.<br />.<br />.<br />2) Entanglement Swapping<br />.<br />.<br />.<br />.<br />Quantum repeaters<br />Fidelity is close to 1 at long distances, but… the time increases exponentially with distance<br />Entanglement of the segments is probabilistic: each step occurs at a different moment.<br />“Scalability” : requires quantum memories, which allow an asynchronous preparation of the network<br />Quantum Memories<br />16<br />
  20. 20. How do we entangle two memories?<br />17<br />
  21. 21. Probabilistic Entanglement: DLCZ Protocol<br />18<br />Creation of a collective excitation<br />Entanglement of two ensembles<br />Collective Excitation<br />L.M. Duan et al., Nature 414, 413 (2001)<br />|e><br />field 1<br />write<br />|s><br />|g><br />Experimental demonstration of first quantum repeater segment in 2007<br />
  22. 22. 19<br />Retrieval<br />Storage<br />Writing<br />Re-emission of quantum field<br />Quantum<br />Field<br />Control<br />Field<br />Deterministic entanglement: Single photon and electromagnetically induced transparency (EIT)<br />Mapping of a delocalized single photon<br />K.S. Choi et al., “Mapping photonic entanglement into and out of a quantum memory”, Nature 452, 7183 (2008)<br />
  23. 23. Continuous Variable Entanglement<br />Deterministic entanglement source<br />Uses variables with continuous degrees of freedom - quadratures of an electromagnetic field<br />Characterized by homodyne detection<br />20<br />Coherent State<br />Squeezed State<br />
  24. 24. Current results with EIT in continuous variables<br />Delay of a squeezed state<br />Storage of a single-sideband<br />Storage without excess noise<br />Coherent state<br />Storage of squeezed vacuum<br />−0.16 ± 0.01 dB ~4% <br />−0.21 ± 0.04 dB<br />G. Hétet et al., Phys. Rev. A 74, 033809 (2005)<br />E. Figueroa et al., New J. Phys. 11, 013044 (2009) <br />LKB<br />J. Cviklinski et al., Phys. Rev. Lett. 101, 133601 (2008)<br />K. Honda et al., Phys. Rev. Lett. 100, 093601 (2008)<br />J. Appel et al., Phys. Rev. Lett. 100, 093602 (2008) <br />21<br />
  25. 25. Our system for continuous variable entanglement storage<br />22<br />
  26. 26. Creation of two ensembles<br />23<br />
  27. 27. Plan: Towards a Quantum Memory<br />Quantum Memory<br />Source<br />Squeezed Vacuum<br />Characterization<br />Interfacing<br />Memory<br />24<br />
  28. 28. Plan: Towards a Quantum Memory<br />Quantum Memory<br />Source<br />Squeezed Vacuum<br />Characterization<br />Interfacing<br />Memory<br />25<br />
  29. 29. Generation of Squeezed Vacuum with an OPO<br />Source of Squeezed Vacuum<br />Compatible with a Cesium-based quantum memory<br />Optical Parametric Oscillator (OPO)<br />26<br />
  30. 30. Usage of nonlinear optics<br />Second-harmonic Generation<br />Parametric Down-Conversion<br />Coherent State<br />Squeezed Vacuum<br />27<br />
  31. 31. Experimental Layout<br />28<br />
  32. 32. Experimental Layout<br />29<br />
  33. 33. Second-Harmonic Generation<br />Ring cavity<br />Stabilization via Tilt-Locking<br />Temperature regulation<br />30<br />
  34. 34. Doubling Cavity<br />Second-harmonic Power<br />31<br />
  35. 35. Doubling Cavity<br />Second-harmonic Power<br />330 mW<br />330 mW of blue<br />50% conversion efficiency<br />32<br />
  36. 36. Experimental Layout<br />33<br />
  37. 37. OPO Cavity<br />Linear<br />Quadratic<br />34<br />Balance between strong squeezing and experimental stability<br />
  38. 38. OPO Cavity<br />Output coupler T = 7%<br />Below-threshold operation<br />Stabilization by Pound-Drever-Hall<br />Counter-propagating lock beam<br />35<br />
  39. 39. Lock Beam<br />Stray photons in the Squeezed Vacuum<br />Reduction of lock beam intensity<br />Antireflective treatment<br />Active Switch<br />36<br />
  40. 40. Plan: Towards a Quantum Memory<br />Quantum Memory<br />Source<br />Squeezed Vacuum<br />Characterization<br />Interfacing<br />Memory<br />37<br />
  41. 41. Experimental Layout<br />38<br />
  42. 42. Squeezed Vacuum Generation<br />S. Burks et al., “Squeezed light at the D2 cesium line for atomic memories”, Opt. Express 17, 3777 (2008)<br />39<br />Analysis frequency: 1MHz<br />
  43. 43. Squeezed Vacuum Generation<br />S. Burks et al., “Squeezed light at the D2 cesium line for atomic memories”, Opt. Express 17, 3777 (2008)<br />40<br />Analysis frequency: 1MHz<br /><ul><li>3 dB of squeezing</li></ul>(50% reduction of quantum noise)<br />
  44. 44. Squeezed Vacuum Generation<br />41<br />Compatibility with the memory?<br />
  45. 45. Squeezed Vacuum Generation<br />Will be used for EIT in Cesium<br />42<br />Compatibility with the memory?<br />Absorption<br />Dispersion<br />
  46. 46. Squeezed Vacuum Generation<br />Will be used for EIT in Cesium<br />Frequency fixed by linear region of the dispersion<br />43<br />Absorption<br />Dispersion<br />500 kHz<br />
  47. 47. Squeezed Vacuum Generation<br />Squeezing starting at 30 kHz<br />Compatibility with bandwidth-limited EIT!<br />44<br />
  48. 48. State Reconstruction<br />45<br />
  49. 49. State Reconstruction<br />Photon pairs for Squeezed Vacuum<br />Thermal state mixed with the vacuum state<br />Complete characterization of our state<br />46<br />Wigner function for 2 dB of squeezing<br />
  50. 50. Plan: Towards a Quantum Memory<br />Quantum Memory<br />Source<br />Squeezed Vacuum<br />Characterization<br />Interfacing<br />Memory<br />47<br />
  51. 51. Creation of Pulses<br />Temporal mode adapted to the memory<br />Conversion of a continuous source into a pulsed source<br />Very difficult due to the fragility of quantum states<br />48<br />
  52. 52. Pulses with an Optical Chopper<br />49<br />Acoustic noise suppression<br />Mechanical vibration attenuation<br />time<br />
  53. 53. Pulses with an Optical Chopper<br />1 µs width<br />time<br />Optical losses~2%<br />Pulses of 500 ns!<br />50<br />
  54. 54. Pulses via AOM<br /><ul><li>Low optical losses: ~10%
  55. 55. Precise timing control: 25 ns</li></ul>51<br />
  56. 56. Plan: Towards a Quantum Memory<br />Quantum Memory<br />Source<br />Memory<br />52<br />
  57. 57. Creation of Two Ensembles<br />53<br />
  58. 58. Necessary Elements<br />Atoms<br />Large and dense cloud<br />EIT<br />Lasers and transitions<br />Magnetic field cancelation<br />Avoid ground state decoherence<br />Timing and Synchronization<br />54<br />
  59. 59. 55<br />
  60. 60. Chamber<br />56<br />
  61. 61. Chamber<br />MOT<br />57<br />
  62. 62. Chamber<br />MOT<br />Lasers<br />58<br />
  63. 63. Chamber<br />MOT<br />Lasers<br />Multiplexing<br />59<br />
  64. 64. Chamber<br />MOT<br />Lasers<br />Multiplexing<br />60<br />How can we characterize this cloud?<br />
  65. 65. Optical density measurement<br />61<br />-10 MHz<br />
  66. 66. Optical density measurement<br />-10 MHz<br />Optical density of 20<br />Memory efficiency of 25%<br />62<br />Gorshkovet al., Phys. Rev. A 76, 033805 (2007)<br />
  67. 67. Necessary Elements<br />Atoms<br />Large and dense cloud<br />EIT<br />Lasers and transitions<br />Magnetic field cancelation<br />Avoid ground state decoherence<br />Timing and Synchronization<br />63<br />
  68. 68. Optical Phase Lock<br />Optical <br />beat signal<br />64<br />
  69. 69. 65<br />
  70. 70. Phase Lock<br />66<br /><ul><li>Rests locked for several hours
  71. 71. sub-Hz frequency precision</li></li></ul><li>Necessary Elements<br />Atoms<br />Large and dense cloud<br />EIT<br />Lasers and transitions<br />Magnetic field cancelation<br />Avoid ground state decoherence<br />Timing and Synchronization<br />67<br />
  72. 72. Extinguishing the magnetic field<br />Field due to MOT coils<br />Residual fields<br />68<br />
  73. 73. Extinguishing the magnetic field<br />Cloud remains ~5 ms after cutting the field<br />Fields are difficult to cut quickly<br />69<br />
  74. 74. Extinguishing the magnetic field<br />Cloud remains ~5 ms after cutting the field<br />Fields are difficult to cut quickly<br />70<br />Time constant 300 µs<br />The cloud remains dense!<br />
  75. 75. Raman Spectroscopy<br />Field present<br />Presence of parasite fields<br />milliGauss compensation in 3 dimensions<br />71<br />
  76. 76. Raman Spectroscopy<br />Field present<br />milliGauss compensation in 3 dimensions<br />72<br />Memory time: 10-100 µs<br />
  77. 77. Necessary Elements<br />Atoms<br />Large and dense cloud<br />EIT<br />Lasers and transitions<br />Magnetic field cancelation<br />Avoid ground state decoherence<br />Timing and Synchronization<br />73<br />
  78. 78. Timing of Memory Lasers<br />74<br />
  79. 79. Timing of Memory Lasers<br />Simple Interface<br />Rapid Development<br />Scaleable<br />75<br />
  80. 80. Memory Optical Table<br />76<br />
  81. 81. Conclusion<br />Entanglement of memory ensembles<br />77<br />
  82. 82. Conclusion<br />Entanglement of memory ensembles<br />Squeezed Vacuum generation with an ’OPO<br />Strong squeezing: -3 dB<br />Compatible with EIT<br />Interfaced with the memory<br />78<br />
  83. 83. Conclusion<br />Entanglement of memory ensembles<br />Squeezed Vacuum generation with an ’OPO<br />Strong squeezing: -3 dB<br />Compatible with EIT<br />Interfaced with the memory<br />Characterization of Memory Elements<br />79<br />Creation of two ensembles<br />Memory storage time: 10-100 µs<br />Memory efficiency of 25%<br />

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