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Preparation, manipulation and detection of single atoms on a chip

Preparation, manipulation and detection of single atoms on a chip. Guilhem Dubois Supervisor: Jakob Reichel Atomchips group, Laboratoire Kastler Brossel, ENS Paris. Single atoms : remarkable features. Well-controlled system! Testbed for Quantum Mechanics Qubit candidate?. b. a.

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Preparation, manipulation and detection of single atoms on a chip

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  1. Preparation, manipulation and detection of single atoms on a chip Guilhem Dubois Supervisor: Jakob Reichel Atomchips group, Laboratoire Kastler Brossel, ENS Paris

  2. Single atoms : remarkable features Well-controlled system! Testbed for Quantum Mechanics Qubit candidate? b a Tcoh > 10s Cooling & trapping

  3. Outline • Introduction: experiments with single atoms • Cavity QED and single atom detection • Experimental setup • Detection of waveguided atoms • Preparation and detection of trapped single atoms • Detection with minimum backaction • Quantum Zeno effect

  4. Single atoms toolbox Preparation Interaction Detection

  5. Single atoms toolbox Preparation Interaction with … Detection light fields(in free space, in a cavity)  atom-photon entanglement[Volz et al. PRL96 (2006)] non-classical states of light- Fock states [Deleglise Nature455 (2008)]- polarisation-entangled photons[Wilk Science317 (2007)] another single atom(atom-atom entanglement)  controlled collisions[Mandel et al. Nature425 (2003)] Rydberg blockade[Gaëtan et al. Nat. Phys.5 (2009)]

  6. Single atoms toolbox Preparation : constraints deterministic  specific internal state e.g. clock states specific motional state e.g. trap ground state Interaction Detection

  7. Single atoms toolbox Preparation : feedback deterministic  specific internal state e.g. clock states specific motional state e.g. trap ground state Interaction Detection : here atom counting minimum backaction (spontaneous emission) How can we achieve that ?

  8. Outline • Introduction • Cavity QED and single atom detection • Experimental setup • Detection of waveguided atoms • Preparation and detection of trapped single atoms • Detection with minimum backaction • Quantum Zeno effect

  9. e b Atom-cavity system atom g optical cavity k coupling g Strong coupling regime : g >> k , g  small mode volume  good quality mirrors

  10. Detection of single atoms Evidence of field quantisation & photon counter Quantum light sources Brune et al. PRL76 (1996) Hijlkema PhD thesis (2007) Oettl et al. PRL95 (2005) Cavity QED experiments  single atom - single photon interaction

  11. +,1 e,0 g,1 b,1 splitting 2g coupling g energy energy -,1 b,0 b,0 Interaction single atom - single photon visible! Resonant Jaynes-Cummings spectrum e b

  12. Principle of single atom detection in a cavity Optimum measurement rate1 measurement = 1 photon With losses L : ¡signal = L£ ¡inc

  13. For a free space detector: factor C ! Detection with minimum backaction?  Backaction characterized by Gsp

  14. Outline • Introduction • Cavity QED and single atom detection • Experimental setup • Detection of waveguided atoms • Preparation and detection of trapped single atoms • Detection with minimum backaction • Quantum Zeno effect

  15. AutoCAD’s view Integrated atom chip-cavity system

  16. Atom chip basics 1cm Applications: - BEC - precise transport and positioning - atomic clocks and interferometers - single atom manipulation? Magnetic traps: - versatility - strong confinement close to the surface

  17. Miniaturized Fabry-Perot cavity

  18. Miniaturized Fabry-Perot cavity - tunable - small mode volumew0=4 mm ; d=39 mm - integrated150mm from chip surface Cavity QED Strong coupling regime! finesse F = 38000 coupling g/2p= 160 MHz cavity decayk/2p = 50 MHz atomic decayg/2p= 3 MHz cooperativity C =g2/2kg = 85

  19. Outline • Introduction • Cavity QED and single atom detection • Experimental setup • Detection of waveguided atoms • Preparation and detection of trapped single atoms • Detection with minimum backaction • Quantum Zeno effect

  20. Detection of waveguided atoms Principle APD BEC Atomic waveguide a Detection zone LASER … the easiest way to put SINGLE atoms in the cavity

  21. Detection of waveguided atoms Reference with no atoms

  22. Detection of waveguided atoms Single run with atoms

  23. Detection of waveguided atoms Experiment Threshold  these are single atoms !!!

  24. Outline • Introduction • Cavity QED and single atom detection • Experimental setup • Detection of waveguided atoms • Preparation and detection of trapped single atoms • Detection with minimum backaction • Quantum Zeno effect

  25. Trapping & detecting the atoms in the cavity mode Transfer magnetic trap  Optical dipole trap @ 830nm Experiments with BEC : see Colombe et al. Nature 450 (2007)

  26. BEC in magnetic trap N ~ a few 1000s Y Positioning the BEC in the cavity input fibre output fibre • Initial cloud size ~1mm single-site loading possible. Dipole trap @ 830nm Probe light @ 780nm

  27. How to get to the single atom regime? Vacuum Rabi Splitting with collective enhancement Laser detuning ΔL-A [GHz] Y. Colombe, T. Steinmetz, G. Dubois, F. Linke, D. Hunger and J.Reichel Nature 450 (2007)

  28. F'=0,1,2,3 Cavity tuned to F=2 -> F’=3 transition F=2 Weak MW pulse (@6.8 GHz) ~2% transfer probability/atom F=1 Reservoir (N~10) From the BEC to just a single atom • Problem: Evaporation down to N=1 not possible. • Solution: Extract a single F=2 atom from a ‘reservoir’ of F=1 atoms – and detect it.

  29. dip ! Usual strategy to obtain trapped single atoms “Wait and trap” scheme: • First trapped cavity QED experiments(Caltech, Garching) • Problem: the atom is hot - cooling required(Raman sideband cooling, cavity cooling) • Possible improvement: optical conveyor belt(Bonn, Zurich) • We do differently!We aim at direct preparation in the trap ground state • Analogy with our scheme : position  internal state.

  30. “Preparation and detection” iterative sequence time Detection Detection Reservoir preparation mw mw Etc … F’=3 F=2 F=1 ~10 1000

  31. 0 or1atom in F=2? nAPD ~ 25 nAPD < 1

  32. Analysis of detection pulses <n>=0.35 <n>=25 • Transfer efficiency 10% • Relative transmission1.4% threshold successful transfers (~10%) unsuccessfultransfers (~90%) after ~10 pulses Reliable preparation

  33. single run Lifetime of the atoms during detection or ??

  34. stat. limit Fit or ?? depump limit Fidelity=99.7% + QND measurement Lifetime of the atoms during detection • Average lifetime 1.2 ms • Limited by depumping to F=1

  35. Outline • Introduction • Cavity QED and single atom detection • Experimental setup • Detection of waveguided atoms • Preparation and detection of trapped single atoms • Detection with minimum backaction • Quantum Zeno effect

  36. Zeeman “random walk”: But not visible in lifetime ! How can we measure spontaneous emission?

  37. Measurement of mF p p p Measurement and preparation of a specific Zeeman state (F=2;mF=0) B

  38. Diffusion in the Zeeman manifold Fit

  39. Detection figure of merit : backaction  Better than a perfect free space detection !  Possible to prepare a single atom without changing the motional state !

  40. Detection without perturbation ? with L ~ 0.1 : C ~ 20 expected value C ~ 85 ??? • What is the real measurement rate of the system? • for a lossless observer ¡m = ¡inc = C ¡sp • can we check that ???

  41. Outline • Introduction • Cavity QED and single atom detection • Experimental setup • Detection of waveguided atoms • Preparation and detection of trapped single atoms • Detection with minimum backaction • Quantum Zeno effect

  42. Cavity & atomic excited state F=2;mF=0 mw p F=1;mF=0 Quantum Zeno Effect b a m = Coherence decay ratebetween a and b m = Photon input rate ~ 20 £ Spontaneous emission rate

  43. Summary • Preparation of trapped single atoms starting from a BEC: • preparation in a specific Zeeman state qubit clock states • well localized within the cavity • First detector of single atoms on a chip ability to distinguish F=1 from F=2 states with 99.7% fidelity • Demonstrated a Quantum Zeno effect w/o spontaneous emission.

  44. e laser cavity b a Outlook • Characterize the atomic motional stateare we still in the ground state? • Manipulate of pairs of atoms in the cavity  Cavity-assisted entanglement generation • Combine with other atom chip technology(state dependent mw potentials) • Quantum memory with BEC and Fiber-cavity - Large collection efficiency - Long storage time

  45. Single atom Vacuum Rabi splitting

  46. Atomchip-based single atom detectors • Fluorescence (Wilzbach et al. 0801.3255) • Photoionization (Stibor et al PRA 76 (2007)) • Cavity QED (Purdy et al. APB 90 (2008)) 1 3 2

  47. e laser vacuum b a Single atoms – light/matter interface • Single photon source • Atom-photon entanglement • Photon-photon entanglement • Long-distance atom-atom entanglement via entanglement swapping Quantum networks for quantum cryptography - Probabilistic is OK (DLCZ 2002)  atomic ensembles possible but coherence time ~ms. - Collection efficiency small with single atoms  a cavity helps

  48. Single atom ‘temperature‘ Release and recapture Mean energy < 100 mK (trap depth 2.6 mK)

  49. Single atom Rabi oscillations

  50. Single atoms : some fascinating achievements Hong-Ou-Mandel effect Evidence of field quantisation & photon counting Beugnon et al. Nature440 (2006) Massive multi-particle entanglement Brune et al. PRL76 (1996) Mandel et al. Nature 425 (2003)

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