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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

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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"— 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. 9th, 2010 平面型トラップによるイオンの捕獲 Confinement of Ca+ ions in a planar trap 大阪大学 大学院基礎工学研究科 占部研究室 田中 歌子 Utako Tanaka

2 Outline 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 1. Introduction Ion trap     Confine charged particles by using electromagnetic field 60’s Proposed by Dehmelt 80’s Spectroscopy by Wineland, Werth, and Walther Paul trap (rf electric field) Penning Trap( static electric field and static magnetic field) Since these two types were established, structures of ion trap electrodes had been basically same. 90’s Linear Paul trap x y z

4 1. Introduction Planar trap ○ Complicated layout ○ Optical access
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) Linear Paul trap - Planar trap + + - ○ Complicated layout ○ Optical access ○ Coupling ion traps with other physical systems ▲ Shallow potential

5 2. Ion trap Conventional linear trap Line charge at z0
2 dimention, analytic Line charge at z0 (K:const) Complex plane y d x Positive line charge d d d Negative line charge Pseudopotential Electrostatic potential at a moment

6 2. Ion trap Planar trap y x Complex plane d’ d d d’ Pseudopotential
Electrostatic potential at a moment

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

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

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

10 3. Precition spectroscopy
Accuracy 88Sr Ca Yb Hg + 137Ba + 115In Al +   2S1/2-2D5/2 2S1/2-2D5/2 S1/2-2D3/2 (F=2-F=0) 1S0-3P0 Doppler shift Doppler cooling limit   ~10-18 Second order Residual thermal motion and micromotion Quadrupole moment shift D-state order of several hertz or more no quadrupole moment dc potential gradient Zeeman shifts no first order Zeeman shift (mF=0-mF’=0) Compensation Compensation First order Second order Compensation Varing magnetic field due to currents at rf electrode Stark shifts ~10-18 Residual thermal motion and micromotion ~10-18 Motional –induced 0.38 -0.08 Blackbody radiation  (300K 10-16) 7.4 9.3 -5.4

11 4. Trap layout Simulation Solver : Ansoft Maxwell3D
Middle Top End L End R g RF wc Center wr RF x End L End R RF DC Bottom y z wm Q: ion charge, m: ion mass : RF potential : DC potential : RF frequency

12 4. Trap layout Functions of electrodes g RF wc Center wr RF x y z wm
MiddleTop End L End R g RF wc Center wr RF x End L End R Bottom y z wm 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 4. Trap layout x-y plane y-z plane

14 4. Trap layout y = 0.4 mm 0.5 mm 0.5 mm

15 4. Trap layout 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 4. Trap layout Potential depth
x direction [mm] z direction [mm] Vrf=800Vp-p,Ω/2π=20 [MHz] , wr=0.82mm , wc=0.26mm , g=0.05mm , r0=0.414mm

17 4. Trap layout Ion motion x y z conventional trap z 2z0 ion position
Vrf cosΩt  Mathieu equation i = x, y, z U0 Q: charge m: mass κ: geometric factor Trap condition Ion motion micromotion Secular motion (Reduced by laser cooling) :Secular frequency :phase

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

19 4. Trap layout 11.5 mm 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

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

21 4. Trap layout Vacuum level 10-11 Torr 106 mm

22 5. Characterization using Ca+ ions
Loading Laser cooling photoionization Energy level diagram of 40Ca Energy level diagram of 40Ca+ Continuum 2P3/2 854 2P1/2 390 nm 850 2D5/2 866 4s4p 1P1 2D3/2 397nm τ~1s 423 nm 729 4s2 1S0 2S1/2

23 5. Characterization using Ca+ ions
Experimental setup Photomultiplier y z x RF 20MHz 800 Vpp(typ.) x z y Oven Interference filter Amp Ca beam Helical resonator Image intensifier 866 nm Beam splitter Vacuum chamber ~2×10-11 Torr 397 nm 423 nm 375 nm Lens Trap 397 nm To pump Trap

24 5. Characterization using Ca+ ions
Trapping ions Fluorescence from trapped ions Photoionization Ions are trapped 405 μm above from the surface. (Design 400 μm above)

25 5. Characterization using Ca+ ions
Quantum jumps 15μm 2P3/2 854 2P1/2 850 τ~1s 2D5/2 866 2D3/2 397nm τ~1s 2S1/2 Energy level diagram of 40Ca+

26 5. Characterization using Ca+ ions
Middle Top Measurement of secular frequency End L End R An ac voltage of 0.4 Vamp is applied to the middle top. When it resonates to the secular frequency, ions are heated and fluorescence drops. RF Center ωz RF x End L End R y Bottom z Vrf=256Vp-p、Vcenter=9.8V、 Vend =14V Vtop=Vbottom=0V

27 After compensation[V]
6. Micromotion compensation x z y Detection with side beam 397 nm Side beam Middle Top End L End R electrode Before compensation[V] After compensation[V] End left 8.8 End right Center 6.2 Top middle Bottom middle 3.0 Vrf 90 RF Center ωz RF x End L End R y z Bottom

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

29 Summary x z 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 Trapping Ca+ ions 405 μm above the surface (almost same as the designed value) Measurement of secular frequencies (Difference from simulation) Method of micromotion compensation in the y-direction Near future Laser beams Trap electrode z x y Ca beam

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