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

1. Towards a Quantum Memory for Non-Classical Light With Cold Atoms Sidney Burks October 13, 2010 Thesis Director: Elisabeth Giacobino Thesis Co-director: JulienLaurat Quantum Optics Group Laboratoire Kastler-Brossel Université Pierre et Marie Curie, Paris 1

2. From Classical Bits to Quantum Bits Classical information is based on the bit Discrete values of 1 or 0 Photonic bits Quantum information introduces the qubit Superposition of states 2

3. A Quantum Memory Desideratum : Storage without measurement, on-demand retrieval i.e. a coherent and reversible transfer between light and matter. General Strategy: Transfer the quantum superposition of light onto a superposition of states in a storage medium Photonic qubit 3

4. A Quantum Memory Desideratum : Storage without measurement, on-demand retrieval i.e. a coherent and reversible transfer between light and matter. General Strategy: Transfer the quantum superposition of light onto a superposition of states in a storage medium The states |a> and |b> are typically ground states in order to avoid a rapid decoherence General Recipe: Two ground states are connected via an excited state by a control field Photonic qubit 4

5. A review of Quantum Memories Single Atom Cavity Quantum Electrodynamics (strong coupling) “Dynamic” EIT Experiments at LKB Atomic Ensemble: Collective Excitation Rephasing protocols - CRIB and AFC - Rare earth elements in solids at cryogenic temperatures Long lifetime 5

7. We know however, how to create twin photon sources6

9. We know however, how to create twin photon sources

10. Memory loaded with a photon7

11. Applications of Quantum Memories Deterministic “Photon Gun” 8

12. Synchronization of photon emissions Two-photon interference 9

13. Synchronization of photon emissions Two-photon interference Quantum gates 10

14. Quantum Networks Distribution of entanglement throughout a network Propagation of entanglement in complex quantum systems Simulation of collective phenomenon H.J. Kimble, The Quantum Internet, Nature 453, 1023 (2008) 11

15. 12 Long-distance Quantum Communication Quantum states are fragile Impossible to clone arbitrary quantum states Amplification impossible!

16. Long-distance Quantum Communication 100 km, telecom fiber: 99.5 % losses For 1000 km, and with a 10GHz qubit source, it would take 300000 years to transmit 1 qubit Connection time increases exponentially with distance 13

17. Long-distance Quantum Communication 100 km, telecom fiber: 99.5 % losses For 1000 km, and with a 10GHz qubit source, it would take 300000 years to transmit 1 qubit Connection time increases exponentially with distance Quantum repeaters 14

18. Divide into segments and Generate Entanglement . . . . . . L0 L0 L0 L . . . . . . 2) Entanglement Swapping . . . . Quantum repeaters Fidelity is close to 1 at long distances, but… the time increases exponentially with distance Entanglement of the segments is probabilistic: each step occurs at a different moment. 15

19. Divide into segments and Generate Entanglement . . . . . . L0 L0 L0 L . . . . . . 2) Entanglement Swapping . . . . Quantum repeaters Fidelity is close to 1 at long distances, but… the time increases exponentially with distance Entanglement of the segments is probabilistic: each step occurs at a different moment. “Scalability” : requires quantum memories, which allow an asynchronous preparation of the network Quantum Memories 16

20. How do we entangle two memories? 17

21. Probabilistic Entanglement: DLCZ Protocol 18 Creation of a collective excitation Entanglement of two ensembles Collective Excitation L.M. Duan et al., Nature 414, 413 (2001) |e> field 1 write |s> |g> Experimental demonstration of first quantum repeater segment in 2007

22. 19 Retrieval Storage Writing Re-emission of quantum field Quantum Field Control Field Deterministic entanglement: Single photon and electromagnetically induced transparency (EIT) Mapping of a delocalized single photon K.S. Choi et al., “Mapping photonic entanglement into and out of a quantum memory”, Nature 452, 7183 (2008)

23. Continuous Variable Entanglement Deterministic entanglement source Uses variables with continuous degrees of freedom - quadratures of an electromagnetic field Characterized by homodyne detection 20 Coherent State Squeezed State

24. Current results with EIT in continuous variables Delay of a squeezed state Storage of a single-sideband Storage without excess noise Coherent state Storage of squeezed vacuum −0.16 ± 0.01 dB ~4% −0.21 ± 0.04 dB G. Hétet et al., Phys. Rev. A 74, 033809 (2005) E. Figueroa et al., New J. Phys. 11, 013044 (2009) LKB J. Cviklinski et al., Phys. Rev. Lett. 101, 133601 (2008) K. Honda et al., Phys. Rev. Lett. 100, 093601 (2008) J. Appel et al., Phys. Rev. Lett. 100, 093602 (2008) 21

25. Our system for continuous variable entanglement storage 22

26. Creation of two ensembles 23

27. Plan: Towards a Quantum Memory Quantum Memory Source Squeezed Vacuum Characterization Interfacing Memory 24

28. Plan: Towards a Quantum Memory Quantum Memory Source Squeezed Vacuum Characterization Interfacing Memory 25

29. Generation of Squeezed Vacuum with an OPO Source of Squeezed Vacuum Compatible with a Cesium-based quantum memory Optical Parametric Oscillator (OPO) 26

30. Usage of nonlinear optics Second-harmonic Generation Parametric Down-Conversion Coherent State Squeezed Vacuum 27

31. Experimental Layout 28

32. Experimental Layout 29

33. Second-Harmonic Generation Ring cavity Stabilization via Tilt-Locking Temperature regulation 30

34. Doubling Cavity Second-harmonic Power 31

35. Doubling Cavity Second-harmonic Power 330 mW 330 mW of blue 50% conversion efficiency 32

36. Experimental Layout 33

37. OPO Cavity Linear Quadratic 34 Balance between strong squeezing and experimental stability

38. OPO Cavity Output coupler T = 7% Below-threshold operation Stabilization by Pound-Drever-Hall Counter-propagating lock beam 35

39. Lock Beam Stray photons in the Squeezed Vacuum Reduction of lock beam intensity Antireflective treatment Active Switch 36

40. Plan: Towards a Quantum Memory Quantum Memory Source Squeezed Vacuum Characterization Interfacing Memory 37

41. Experimental Layout 38

42. Squeezed Vacuum Generation S. Burks et al., “Squeezed light at the D2 cesium line for atomic memories”, Opt. Express 17, 3777 (2008) 39 Analysis frequency: 1MHz

44. Squeezed Vacuum Generation 41 Compatibility with the memory?

45. Squeezed Vacuum Generation Will be used for EIT in Cesium 42 Compatibility with the memory? Absorption Dispersion

46. Squeezed Vacuum Generation Will be used for EIT in Cesium Frequency fixed by linear region of the dispersion 43 Absorption Dispersion 500 kHz

47. Squeezed Vacuum Generation Squeezing starting at 30 kHz Compatibility with bandwidth-limited EIT! 44

48. State Reconstruction 45

49. State Reconstruction Photon pairs for Squeezed Vacuum Thermal state mixed with the vacuum state Complete characterization of our state 46 Wigner function for 2 dB of squeezing

50. Plan: Towards a Quantum Memory Quantum Memory Source Squeezed Vacuum Characterization Interfacing Memory 47

51. Creation of Pulses Temporal mode adapted to the memory Conversion of a continuous source into a pulsed source Very difficult due to the fragility of quantum states 48

52. Pulses with an Optical Chopper 49 Acoustic noise suppression Mechanical vibration attenuation time

53. Pulses with an Optical Chopper 1 µs width time Optical losses~2% Pulses of 500 ns! 50

55. Precise timing control: 25 ns51

56. Plan: Towards a Quantum Memory Quantum Memory Source Memory 52

57. Creation of Two Ensembles 53

58. Necessary Elements Atoms Large and dense cloud EIT Lasers and transitions Magnetic field cancelation Avoid ground state decoherence Timing and Synchronization 54

59. 55

60. Chamber 56

61. Chamber MOT 57

62. Chamber MOT Lasers 58

63. Chamber MOT Lasers Multiplexing 59

64. Chamber MOT Lasers Multiplexing 60 How can we characterize this cloud?

65. Optical density measurement 61 -10 MHz

66. Optical density measurement -10 MHz Optical density of 20 Memory efficiency of 25% 62 Gorshkovet al., Phys. Rev. A 76, 033805 (2007)

67. Necessary Elements Atoms Large and dense cloud EIT Lasers and transitions Magnetic field cancelation Avoid ground state decoherence Timing and Synchronization 63

68. Optical Phase Lock Optical beat signal 64

69. 65

72. Extinguishing the magnetic field Field due to MOT coils Residual fields 68

73. Extinguishing the magnetic field Cloud remains ~5 ms after cutting the field Fields are difficult to cut quickly 69

74. Extinguishing the magnetic field Cloud remains ~5 ms after cutting the field Fields are difficult to cut quickly 70 Time constant 300 µs The cloud remains dense!

75. Raman Spectroscopy Field present Presence of parasite fields milliGauss compensation in 3 dimensions 71

76. Raman Spectroscopy Field present milliGauss compensation in 3 dimensions 72 Memory time: 10-100 µs

77. Necessary Elements Atoms Large and dense cloud EIT Lasers and transitions Magnetic field cancelation Avoid ground state decoherence Timing and Synchronization 73

78. Timing of Memory Lasers 74

79. Timing of Memory Lasers Simple Interface Rapid Development Scaleable 75

80. Memory Optical Table 76

81. Conclusion Entanglement of memory ensembles 77

82. Conclusion Entanglement of memory ensembles Squeezed Vacuum generation with an ’OPO Strong squeezing: -3 dB Compatible with EIT Interfaced with the memory 78

83. Conclusion Entanglement of memory ensembles Squeezed Vacuum generation with an ’OPO Strong squeezing: -3 dB Compatible with EIT Interfaced with the memory Characterization of Memory Elements 79 Creation of two ensembles Memory storage time: 10-100 µs Memory efficiency of 25%