Manipulating Single Atoms

Transcription

1 Manipulating Single Atoms MESUMA 2004 Dresden, , 09:45 Universität Bonn D. Meschede Institut für Angewandte Physik

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3 Overview 1. A Deterministic Source of Single Neutral Atoms 2. Inverting MRI A Neutral Atom Quantum Register 3. Coherent Atom Manipulation 4. The Future

4 Overview 1. A Deterministic Source of Single Neutral Atoms

5 1. Deterministic Source of Single Neutral Atoms Single Neutral Atoms Single Ions Toschek,... Walther, Haroche Single Molecules Moerner,... Grangier Lu Rempe Meschede Ertmer Kimble McClelland Chapman

6 1. Deterministic Source of Single Neutral Atoms Apparatus for manipulating single neutral atoms MOT- Laser beams Imaging Optics Photon- Counter

7 1. Deterministic Source of Single Neutral Atoms Photon Count Rtae [100 khz] Laser Sequence MOT Dipole Trap N=4 N=3 N=2 N= Time [s] Atoms Time (s)

8 1. Deterministic Source of Single Neutral Atoms...in the MOT 0 counts µm 9 µm

9 1. Deterministic Source of Single Neutral Atoms Optical conveyor belt (single atom tweezer) AOM MOT- Laser beams Imaging Optics Photon- Counter AOM Nd:YAG-Laser

10 1. Deterministic Source of Single Neutral Atoms Characteristics of the optical dipole potential MOT 5 Watt Multimode Nd:YAG Laser 500 nm U0= 1.3 mk Ωz z

11 1. Deterministic Source of Single Neutral Atoms...in the MOT...in the dipole trap 2.7 µm 0 counts µm 9 µm 0 counts µm

12 1. Deterministic Source of Single Neutral Atoms...in the dipole trap 10 µm 10 µm dipole trap laser beam dipole trap laser beam

13 1. Deterministic Source of Single Neutral Atoms The Single Atom Conveyor Belt v + v v v v = λ v 2 v v v + 2 v + 2

14 1. Deterministic Source of Single Neutral Atoms 1 Atom 3 Atoms

15 Overview 2. Inverting MRI A Neutral Atom Quantum Register

16 Overview 2. Inverting MRI A Neutral Atom Quantum Register

17 2. A Neutral Atom Quantum Register F = 5 "push-out" laser F = 4 F = 3 survival probability: P(F = 3) > 99 % P(F = 4) < 0.5 %

18 2. A Neutral Atom Quantum Register 4 m F = -4 F = GHz m F = F = 3 magnetic field gradient db / dx

19 2. A Neutral Atom Quantum Register 10µm take camera picture determine position of all atoms

20 2. A Neutral Atom Quantum Register 10µm take camera picture determine position of all atoms calculate resonance frequency of center atom detuning [MHz] δυ = δx khz 4 µm position [µm]

21 2. A Neutral Atom Quantum Register 10µm take camera picture determine position of all atoms calculate resonance frequency of center atom prepare atoms in F = 4, m F = -4 >

22 2. A Neutral Atom Quantum Register 10µm take camera picture determine position of all atoms calculate resonance frequency of center atom prepare atoms in F = 4, m F = -4 > apply microwave pulse

23 2. A Neutral Atom Quantum Register 10µm take camera picture determine position of all atoms calculate resonance frequency of center atom prepare atoms in F = 4, m F = -4 > apply microwave pulse apply push-out laser

24 2. A Neutral Atom Quantum Register 10µm take camera picture determine position of all atoms calculate resonance frequency of center atom prepare atoms in F = 4, m F = -4 > apply microwave pulse F=3 apply push-out laser take camera picture

25 2. A Neutral Atom Quantum Register some typical pictures 10 µm

26 2. A Neutral Atom Quantum Register single atom population transfer [%] τ pulse = 21µs τ pulse = 42µs τ pulse = 83µs position offset [µm] Numerical simulation Gaussian fit to data δυ khz = 4 δx µm FWHM = 1.8 µm!

27 2. A Neutral Atom Quantum Register ( 0 1 )

28 Overview 3. Coherent Atom Manipulation Quantum State 1 0 Time

29 3. Coherent Atom Manipulation Driven Rabi-Oscillation single atom population transfer [%] pulse duration [µs]

30 3. Coherent Atom Manipulation π/2 population in F=3 [%] delay [ms] t

31 3. Coherent Atom Manipulation COLD atoms ``HOT atoms δ δ COLD F = 4 δ ΗΟΤ F = 3

32 3. Single Qubit Operations delay π/2 π π/2 population in F=3 [%] t π delay [ms]

33 3. Coherent Atom Manipulation population in F=3 [%] π delay [ms] π delay [ms]

34 3. Coherent Atom Manipulation Ramsey signal (w/o π-pulse) Echo signal (with π-pulse) population in F=3 [%] π-pulse π/2-pulse time of second π/2-pulse [ms]

35 3. Coherent Atom Manipulation 40 population in F=3 [%] without transport with transport 5 π/2 π π/ time [ms]

36 3. Coherent Atom Manipulation Controlling neutral atoms:

37 Overview 4. The Future towards Entanglement

38 4. Towards Entanglement We need better position control: Measuring the house number of the atom Rua dos Atomos

39 4. Towards Entanglement We need perfect position control: Measuring the house number of the atom 2.7 µm 0 counts µm ~ 120 nm (Limit: 1s int.-time, drifts)

40 4. Towards Entanglement d=nλ/2 integrated number of pairs of atoms distance between atoms d ( λ ) ~ 55 nm Extension of wave-packet: ~ nm Fundamental limit!

41 4. Towards Entanglement target position 10µm number of atoms σ=0.3 µm = 220 nm (stat.) Initial distribution of atoms in the DT Distribution after position feedback 20 σ=5 µm distance [µm] distance? "position control" take camera picture calculate distance to target position take second camera picture

42 4. Towards Entanglement Two perpendicular conveyor-belts "sort" atoms coupling between arbitrary pairs of atoms No longer fiction! Y. Miroshnychenko, M. Khudaverdyan

43 4. Towards Entanglement Conveyor Belt atom Delivery of atoms ON DEMAND!! 1, 2, 3,... Atoms 0, 1, 2,... Photons

44 4. Towards Entanglement Guo et al. PhysRevLett 85, 2392 (2000) Osnaghi et al. PhysRevLett 87, (2001) 1 2 ( ) Creation of entangled and fully controlled atoms

45 3. Coherent Atom Manipulation Adressing individual atoms by adiabatic passage 1. Choose center frequency of frequency sweep 2. Magnetic field gradient for spatial discrimination

46 3. Coherent Atom Manipulation Adiabatic passage by microwave sweep 9.2 GHZ (F=4, m F =4 F=5, m F =5) population in F=3 (%) central detuning δ (khz) 0

47 microwave sweep, homogeneous B-field atom at rest 2004 population in F=3 (%) Ω max =2*pi*30 khz τ pulse = 2 ms δ max = 2*pi*35 khz central detuning δ 0 (khz)

48 microwave constant, inhomogeneous B-field atom pulled through resonance, initially in

49 4. Towards Entanglement F F = = g 2 /κγ 2 >

50 4. Towards Entanglement with novel µ-cavities Alternative approach: roller coaster modes in a bulge on an optical fiber: high Q-factor, passively stable, small mode volume strain tunable, advantageous mode geometry

51 4. Towards Entanglement with novel µ-cavities - Describe thickness variation by refractive index gradient. - Solve Eikonal equation in paraxial approximation. resonance condition: L ( z = N res λ opt c ) FSR 100 GHz for 2 z c = 140 µm and ρ max = 8 µm

52 4. Towards Entanglement with novel µ-cavities Intensity along z (TM mode, m = 84, p = 1, q = 80): 1 normalized intensity z (µm) ρ max = 8 µm, ρ c = 0.96 ρ max, λ = 852 nm, l = 140 µm,

53 4. Towards Entanglement with novel µ-cavities Intensity distribution (TM mode, m = 84, p = 1, q = 80): I / I max Mode Volume700 µm 3 FSR 100 GHz ρ (µm) z (µm) ρ max = 8 µm, ρ c = 0.96 ρ max, λ = 852 nm, l = 140 µm,

54 4. Towards Entanglement with novel µ-cavities Probe intensity distribution of WGMs in barrel resonator with second tapered fiber: coupling and probe fiber position have to be controlled on sub-µm scale

55 The End Thank you for your attention! Hard and enthusiastic work by: D. Schrader, W. Alt, I. Dotsenko, M. Khudaverdyan, Y. Miroshnychenko, L. Förster, Y. Louyer, F. Warken, A. Rauschenbeutel V. Gomer, S. Kuhr, W. Rosenfeld, W. Smith