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大阪大学 大学院基礎工学研究科 占部研究室 田中 歌子 Aug. 9 th, 2010 Utako Tanaka.

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Presentation on theme: "大阪大学 大学院基礎工学研究科 占部研究室 田中 歌子 Aug. 9 th, 2010 Utako Tanaka."— Presentation transcript:

1 大阪大学 大学院基礎工学研究科 占部研究室 田中 歌子 Aug. 9 th, 2010 Utako Tanaka

2  1. Introduction  2. Ion trap (Conventional trap, Planar trap)  3. Precision spectroscopy  4. Trap layout  5. Characterization using Ca + ions  6. Micromotion compensation  7. New design  8 . Summary

3  Ion trap Confine charged particles by using electromagnetic field 60’s Proposed by Dehmelt 80’s Spectroscopy by Wineland, Werth, and Walther 90’s Paul trap (rf electric field ) Penning Trap ( static electric field and static magnetic field ) Linear Paul trap x y z Since these two types were established, structures of ion trap electrodes had been basically same.

4  Planar trap J. Chiaverini et al., Quantum Inf.Comput. 5, (2005) C. E. Pearson et al., Phys. Rev. A 73, (2006) S. Seidelin et al., Phys. Rev. Lett. 96, (2006) Kenneth R. Brown et al., Phys. Rev. A 75, (2007) ○ Complicated layout ○ Optical access ○ Coupling ion traps with other physical systems Linear Paul trap ▲ Shallow potential Planar trap

5  Conventional linear trap d x y Positive line charge Negative line charge dd d Complex plane Electrostatic potential at a moment Pseudopotential (K:const) Line charge at z 0 2 dimention, analytic

6  Planar trap d x y d’d Complex plane d’ Electrostatic potential at a moment Pseudopotential

7 Large solid angle Optical access Precision spectroscopy Quantum Optics Complicated layout Electromagnetic field probe Quantum information processing Shuttling ions Junctions Coupling ion traps with other physical systems Quantum simulation 2D trap Superconductivity material

8 Stability Allan deviation T. Rosenband et al., Science 319, 1808 (2008) Frequency Ratio of Al + and Hg + Single-Ion Optical Clocks; Metrology at the 17th Decimal Place (S/N) T Transition frequency Linewidth Signal to noise ratio Averaging time Cycle time to make a Single determination of the line center

9 Stability Lens (insulator) cannot be close to the trapping region because it affects on the trapping potential. Detection efficiency Solid angle ~ 0.01 Optics loss 0.7 Quantum efficiency 0.5 Lens Filter Photomultiplier Trap Viewport ~ 0.5 ! Allan deviation

10 Accuracy dc potential gradient Zeeman shifts Quadrupole moment shift Doppler shift 88 Sr + 40 Ca Yb Hg + 2 S 1/2 - 2 D 5/2 115 In + 27 Al + 1S0-3P0 1S0-3P0 no quadrupole moment D-state order of several hertz or more 137 Ba + S 1/2 - 2 D 3/2 (F=2-F=0) Second order no first order Zeeman shift (m F =0-m F’ =0) Compensation Stark shifts First order 2 S 1/2 - 2 D 5/2 Residual thermal motion and micromotion Second order Motional –induced Blackbody radiation (300K ) Varing magnetic field due to currents at rf electrode Doppler cooling limit ~ ~ Residual thermal motion and micromotion ~ Compensation

11  Simulation Solver : Ansoft Maxwell3D Q : ion charge, m : ion mass : RF potential : DC potential : RF frequency RF DC End L End L End L End L End R End R End R End R RF Center Middle Top Bottom yz x wmwm wrwr wcwc g

12  Functions of electrodes End L End L End L End L End R End R End R End R RF Center Middle Top Bottom yz x wmwm wrwr wcwc g RF : confinement x-y plane End : confinement z axis, y-direction Center : y-direction Top/Bottom : compensation of micromotion in the x direction(ideally 0V)

13 x - y plane y - z plane

14 y = 0.4 mm 0.5 mm

15  Design of planar trap Position of trapped ion --- several hundred micrometers above the surface q-parameter in Mathieu equation (trapping condition) ~ 0.3 Potential depth --- ~ 1 eV (conventional trap --- ~ 10 eV) Secular frequencies ---A few MHz for radial direction Several hundred kHz for axial direction Overlapping of rf potential null and dc potential minimum --- to minimize micromotion Spacing between electrodes Wire bonding

16  Potential depth V rf =800V p-p,Ω/2π =20 [MHz], w r =0.82mm, w c =0.26mm, g=0.05mm, r 0 =0.414mm x direction [mm]z direction [mm] 4. Trap layout

17  Ion motion Secular motion (Reduced by laser cooling) micromotion Q : charge m : mass κ: geometric factor i = x, y, z : phase Trap condition : Secular frequency ion position Mathieu equation Ion motion r0r0 V rf cosΩt U0U0 z 2z02z0 z xy 4. Trap layout conventional trap

18 k x, k y : wavevector component D. J. Berkeland et al., J. Appl. Phys. 83, 5025 (1998) Excess micromotion Ion motion Stray electric field E dc Excess micromotion This motion cannot be reduced by laser cooling. Compensation voltages are applied to reduce the micromotion. Conventional trap Ideally ( no stray field) (rf null)=(dc potential minimum) Excitation spectra in the presence of micromotion Planar trap It is necessary to design so that the condition is satisfied. Laser detuning [MHz] 100 MHz 4. Trap layout

19 Substrate Alumina ( 635μm thickness 、 99.5 %) Electrode Gold plating Ti/Pb/Au thickness 6±1 ~ 2μm Mount ceramic pin grid array (CPGA) Wire bonding Al wire 11.5 mm 4. Trap layout

20  SEM images of trap electrode Acknowledgement: Dr. Shimakage at NICT Previous trap Current trap 50μm 4. Trap layout

21 106 mm Vacuum level Torr 4. Trap layout

22  Loading Laser cooling photoionization 2 S 1/2 2 P 1/2 2 P 3/2 2 D 3/2 2 D 5/2 397nm τ~1sτ~1s Continuum 423 nm 390 nm 4s 2 1 S 0 4s4p 1 P 1 Energy level diagram of 40 CaEnergy level diagram of 40 Ca +

23 397 nm Oven Trap Vacuum chamber ~2× Torr Ca beam Helical resonator To pump RF 20MHz 800 V pp (typ.) Amp Lens Trap Interference filter Image intensifier x z y Beam splitter Photomultiplier  Experimental setup y z x 397 nm 423 nm 375 nm 866 nm

24  Trapping ions Ions are trapped 405 μm above from the surface. (Design 400 μm above) Photoionization Fluorescence from trapped ions

25  Quantum jumps 2 S 1/2 2 P 1/2 2 P 3/2 2 D 3/2 2 D 5/2 397nm τ~1sτ~1s Energy level diagram of 40 Ca + τ~1sτ~1s 15μm

26  Measurement of secular frequency ωzωz V rf =256V p-p 、 V center =9.8V 、 V end =14V V top =V bottom =0V An ac voltage of 0.4 V amp is applied to the middle top. When it resonates to the secular frequency, ions are heated and fluorescence drops. End L End L End L End L End R End R End R End R RF Center Middle Top Bottom y z x

27 Detection with side beam electrodeBefore compensation[V] After compensation[V] End left8.8 End right8.8 Center6.2 Top middle00 Bottom middle03.0 Vrf90 6. Micromotion compensation x z y 397 nm Side beam ωzωz End L End L End L End L End R End R End R End R RF Center Bottom y x Middle Top z

28 Problems 397 nm Oven Trap Ca beam Helical resonator To pump x z y 397 nm 423 nm 375 nm 866 nm When loading, calcium beam contaminates the surface of the trap, which changes the trap condition such as compensation voltages. Loading region Ca beam hole Moving ions Detection region Trap electrode Laser beams z x y Oven

29 Summary Planar trap for precision spectroscopy Stability --- will be improved Accuracy Choose the species of ion example: Ba + and In + ? Currents at the rf electrode would be problem →Second order Zeeman shift Ca beam Trap electrode Laser beams z x y Trapping Ca + ions 405 μm above the surface (almost same as the designed value) Near future Measurement of secular frequencies (Difference from simulation) Method of micromotion compensation in the y-direction


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