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Microfabricated traps 

Winfried K. Hensinger 

University of Sussex 

Ion Quantum Technology 

http://www.sussex.ac.uk/physics/iqt/

Ion Quantum Technology at Sussex 

We gratefully acknowledge funding from: 

Sussex Ion Quantum 

Technology group: 

PI and group leader: 

Winfried Hensinger 

Grad students: 

Jim McLoughlin 

James Siverns 

Robin Sterling 

Altaf Nizamani 

Undergrads: 

Rajiv Ramasawmy 

Merlin Bevan-Stevenson 

Ben Johnson 

Marcus Hughes 

Graduated July 2007: 

Dan Brown, Nick Davies, Jack 

Friedlander, Jessica Grove- 

Smith, Ben Pruess, David 

Scrivener, Tim Short 

Collaborators: 

Jim Rabchuk, West. Illinois 

Keith Schwab, Cornell 

Chris Monroe, Maryland

Trapped Ion Quantum Computing group at the 

University of Michigan (now at Maryland!!) 

We gratefully acknowledge funding from: 

PI and group leader: 

Chris Monroe 

Former Postdoc, now visiting faculty: 

Winfried Hensinger 

Grad students: 

Jon Sterk 

Mark Acton 

Louis Deslauriers (now at Stanford) 

Martin Madsen (now at Wabash College) 

Daniel Stick (now at Sandia) 

Steven Olmschenk 

Undergrads: 

David Hucul (now at MIT) 

Jacob Burress 

Mark Yeo 

Collaborators: 

Jim Rabchuk, West. Illinois Univ. 

Keith Schwab, LPS and Cornell 

FOCUS

How to trap an ion 

Potential 

Position Position 

∇⋅ E r r 

= 

0

Charged particle trap

Trapology for beginners – an ion trap 

Axial confinement: 

Static “endcaps” 

Transverse confinement: 

Ponderomotive potential 

dc 

rf 

dc 

dc 

rf 

dc 

dc 

rf 

dc 

dc 

rf 

dc

Microfabricated traps 

• Electrode - ion distance 

- Micron dimensions 

• Fabrication 

- Photolithography 

- Manual assembly

Applications 

• Measurement based quantum computing 

D 

- high photon capture rate by getting imaging elements close to the ion 

coincidence 

photon 

detection 

D 

1 2 

|Ψ〉 = (|↓〉 1 |V〉 1 + |↑〉 1 |Η〉 1 )⊗(|↓〉 2 |V〉 2 + |↑〉 2 |Η〉 2 ) 

upon coincidence photon detection 

|Ψ |Ψ〉 |Ψ ⇒ |↓〉 1 |↑〉 2 − |↑〉 2 |↓〉 2 

Entanglement of single-atom quantum bits at a 

distance, D. L. Moehring, P. Maunz, S. Olmschenk, K. 

C. Younge, D. N. Matsukevich, L.-M. Duan, and C. 

Monroe, Nature 449, 68 (2007).

Applications 

• Cavity quantum electrodynamics 

- small mode volume towards strong 

coupling 

Keller et al., Nature 431, 1075 (2004)

Applications 

•Ion trap transducers for quantum 

electromechanical oscillators 

Also see talk by 

Hartmut Haeffner 

W. K. Hensinger, D. Wahyu Utami, H.-S. Goan, K. Schwab, C. Monroe and G. J. 

Milburn, Phys. Rev. A 72, 041405(R) (2005) 

L. Tian, P. Rabl, R. Blatt, and P. Zoller, Phys. Rev. Lett., 92:247902 (2004)

Towards ion trap quantum 

computation 

• Deterministic 8-ion entanglement 

• Two-qubit Phase gate 

• Quantum state tomography 

• Quantum error correction 

• Ion-Photon entanglement 

• Teleportation 

• Various quantum algorithms (such as search) 

• 

• 

• 

Amazing 

achievements 

by the groups of 

Wineland, Blatt, 

Steane, Monroe 

and others. 

With help of 

theorists such as 

Chirac, Zoller, 

Milburn, 

Molmer/Sorensen 

and others

What’s missing?

Applications 

• Scaling ion trap quantum computing 

ENIAC 

(1946)

Large scale arrays 

Wineland et al., NIST J. Res. 103, 259 (1998) 

Kielpinski, Monroe and Wineland, Nature 417, 709 (2002) 

Steane, quant-ph/0412165

Trapology for beginners – symmetric 

Symmetric trap: 

Trap electrodes surround the ion pathway 

symmetrically 

dc 

rf 

dc 

dc 

rf 

dc 

versus asymmetric 

Asymmetric trap (also referred to as surface trap): 

Trap electrodes reside in a single plane and the ion 

pathway is above that plane 

dc rf dc dc rf dc

Fabricating ion chips 

Design and implementation of scalable ion trap 

fabrication methods is of key importance for ion trap 

quantum computing. 

Photolithography 

No manual assembly

gnd 

Two-Layer Ion Trap 

rf 

rf gnd 

V 0 cosWt 

+U 

0 

+U 

+U 

0 

+U

MEMS Gallium-Arsenide ion 

trap in a microchip 

60 µm 

D. Stick 

W. K. Hensinger 

S. Olmschenk 

M. Madsen 

K. Schwab 

C. Monroe

8.6 µm 

60 µm 

130 µm

Ion Trapped in a Semiconductor Chip 

Secular frequencies: ω/2π = 1.0 MHz, 3.3 MHz and 4.3 MHz 

single 

Cd + ion 

RF amplitude 8V at 15.9 MHz, Static: +1V, -0.33V 

Trap depth: 0.08 eV 

Life time: 30 min observed, 10 min typical 

Shuttled to adjacent electrode segment 

60 µm 

D. Stick, W. K. Hensinger, S. Olmschenk, M. J. Madsen, 

K. Schwab and C. Monroe, Nature Physics 2, 36 (2006)

GaAs Ion Trap Fabrication 

~10 mm 

~10 mm 

100 µm 

Si doped GaAs 

AlGaAs 

Ge:Au


~10 mm 

~10 mm 

100 µm 

Si doped GaAs 

AlGaAs 

Ge:Au


~10 mm 

~10 mm 

100 µm 

Si doped GaAs 

AlGaAs 

Ge:Au

MEMS Silicon ion traps 

53 step process! 

In collaboration with: 

Dan Stick, Jon Sterk, Martin Madsen, Winfried Hensinger, Chris Monroe, Bill 

Noonan, Michael Pedersen, Steve Gross, and Michael Huff

Corresponding electric circuit

53 step process! 





First chip 



Ion chip efforts elsewhere 

(incomplete…) 

• NIST: Boron doped Silicon electrodes, 7070 glass insulator and anodic bonding 

Design and operation: D. J. Wineland, et al., in Laser Spectroscopy, Proc. XVII Int. Conf. on Laser 

Spectroscopy, Avemore, Scotland, pp. 393–402, J. Britton et al., arXiv:quant-ph/0605170v1 (2006) 

• NIST: Gold electrodes on a fused silica substrate 

Design and operation: S. Seidelin et al., Phys. Rev. Lett. 96, 253003 (2006) 

• Lucent: Silicon waver with Aluminum/Tungsten electrodes 

Design: J. Kim et al., Quantum Inf. Comput. 5, 515 (2005), operated at Michigan 

• Sandia: Gold coated tungsten electrodes on Silicon substrate 

Design: Proceeding of TIQC 2006, Boulder, USA, operated at Oxford, see poster Curtis et al. 

• MIT: Gold electrodes coated on Quartz substrate 

Design and operation: J. Labaziewicz et al., arXiv:quant-ph0706.3763v1 (2007) 

• NPL: Gold coated Silicon oxide electrodes on Silicon substrate 

Design: M. Brownnut et al, New Journal of Physics 8 (2006) 232, see poster Wilpers et al.

DC 

Contact 

pads 

NIST Planar Trap Chip 

Gold on fused silica 

low pass filters 

John Chiaverini, Signe Seidelin, Didi Leibfried, David Wineland (NIST) 

RF 

trapping 

region

Magnified trap electrodes 

endcap 

control 

control 

endcap 

GND 

NIST Planar Trap Chip 

RF 

100 µm 

CCD pictures of strings of Mg + ions 

(trapped 40 mm above surface) 

5 µm 

Seidelin et al., PRL 96, 253003 (2006). 

John Chiaverini, Signe Seidelin, Didi Leibfried, David Wineland

Lucent ion trap 

Fabricated: Dick Slusher, Lucent 

Operated: Dan Stick, Michigan

NPL design 

Monolithic microfabricated ion trap chip design for scaleable quantum processors 

M. Brownnutt, G. Wilpers, P. Gill, R.C. Thompson, A.G. Sinclair, New J. Phys. 8, 232(2006).

NIST racetrack trap design study 

2.5 mm 

gold on fused silica 

4 crosses 

200 Zones 

400 Electrodes 

2 separate loading zones 

20 zones implemented and 

loaded 

Jason Amini

Shuttling and junctions in large scale 

arrays – multilayer alumina traps 

Important for entanglement of separated ions 

(qubits) in the array 

First shuttling in two-layer geometry along a line 

Rowe et al., Quantum Inf. Comput. 2, 257 (2002). 

Barrett et al., Nature 429, 737 (2005)

A quantum algorithm… 

Ike Chuang, MIT

W. K. Hensinger 

S. Olmschenk 

D. Stick 

D. Hucul 

M. Yeo 

J. Rabchuck 

C. Monroe 

1 mm 

49-electrode 

11-zone 

T-junction

low 

400 mm

Shuttling a single atom… 

Laser

T-Junction ponderomotive 

Potential

Imaging 

Laser 1 

Making the corner 

500µm 

Imaging 

Laser 2 

W. K. Hensinger, S. 

Olmschenk, D. Stick, D. 

Hucul, M. Yeo, M. Acton, L. 

Deslauriers, J. Rabchuk and 

C. Monroe, Applied Physics 

Letters 88, 034101 (2006)

Voltage evolution

Simulation

Kinetic energy evolution during the turn

Separating two ions

Atomic three-point turn

The controls…

Junctions in asymmetric traps and symmetric twoand 

three layer traps 

Asymmetric 

(surface/planar) traps 

Two-layer symmetric 

traps 

Three-layer symmetric 

traps

NIST two layer cross trap 

Mg + and Be + moved through 

junction > 10 4 times without ion loss 

Characterization of heating during 

shuttling in progress 

Brad Blakestad, Didi Leibfried and 

David Wineland 

2 wafers of alumina (0.2 mm thick) 

gold conducting surfaces (2 µm) 

dc 

18 zones, 1 cross 

rf

Ulm linear multizone trap 

Stefan Schulz, Ulrich Poschinger, Frank Ziesel and Ferdinand Schmidt-Kaler

Scaling laws for three-layer junctions 

Cross-sectional view of ion trap: 

Aspect ratio: 

a/b 

b 

a 

D. Hucul, M. Yeo, W.K. Hensinger, J. Rabchuk, S. 

Olmschenk, and C. Monroe, Quantum Information 

and Computation 8, 0501 (2008)

Adiabatic shuttling: Which shuttling 

voltage time profile is the best? 

Average motional state n after shuttling as a function of the time to shuttle the ion T 

hyperbolic tan 

sinusoidal 

linear 

For a given shuttling time, hyperbolic tan protocol always wins 

D. Hucul, M. Yeo, 

W.K. Hensinger, 

J. Rabchuk, S. Olmschenk, 

and C. Monroe, 

Quantum Information and 

Computation 8, 0501 

(2008) 

quant-ph/0702175 (2007)

Average motional state n after shuttling as a function of the time to shuttle the ion T 

hyperbolic tan 

sinusoidal 

For a long enough shuttling time, sinusoidal protocol always wins

How micro can micro-traps be? 

What about nano-traps?

Motional heating in ion traps

Two mechanisms: 

Heating due to Johnson noise? 

S E (ω) ~ d -2 

Heating due to fluctuating patch potential ? 

S E (ω) ~ d -4 

Heating and spectral noise density: 

2 

2 

e ⎛ 

⎞ 

⎜ 

z 

n& ω 

= ⎟ 

⎜ 

SE 

( ωz 

) + S ( Ω ± ) 

2 E ωz 

4mhω 

⎟ 

z ⎝ 2Ω 

⎠

Ion trap with adjustable electrodes 

23 – 250 µm 

Scaling and Suppression of Anomalous Quantum Decoherence in Ion Traps, 

L. Deslauriers, S. Olmschenk, D. Stick, W. K. Hensinger, J. Sterk, and C. Monroe, 

Physical Review Letters 97, 103007 (2006)

15 mm diameter needle tips

Scaling of heating with trap size: 

Without cooling: 

n& ∝ 

Significant suppression of patch potential heating by modest cooling! 

zo 

1 

3 

. 5

MIT cryogenic surface trap 

Before annealing After annealing 

Annealing makes 

a big difference 

J. Labaziewicz, Y. Ge, P. Antohi, D. Leibrandt, K.R. Brown, and I.L. Chuang. 

Suppression of heating rates in cryogenic surface-electrode ion traps. 

Phys. Rev. Lett., 100:013001 (2008)

Field Noise [(V/m) 2 Field Noise [(V/m) /Hz] 2 /Hz] 

10-8 10-8 10-9 10-9 10-10 10-10 10-11 10-11 10-12 10-12 10-13 10-13 10-14 10-14 Way forward 

Field Noise History: 0.6 - 6.0 MHz traps 

SE ( ωz 

) 

Barium 

Mercury 

Ytterbium 

Calcium 

Beryllium 

Cadmium 

Cadmium (needle trap at 300K) 

Cadmium (needle trap at 150K) 

20 50 100 200 500 1000 

Ion-electrode spacing (µm) 

MIT result at 

4 K with 

electrodes 

annealed at 

760 ◦ C

Sussex Ytterbium Experiment

Versatile vacuum system for ion chip 

operation 

See poster Jim McLoughlin

Summary 

• Scaling ion trap quantum computing requires atomic 

physics – condensed matter interface. 

• Highly successful implementation for quantum information 

processing. 

• Microfabricated ion traps have a vast range of applications 

• We do have a good idea about motional heating in ion 

traps 

• Ion Quantum Technology is a vastly growing field with 

many opportunities

Ion Quantum Technology at Sussex 

We are always looking for interested students, potential 

postdocs, academic or commercial collaborators. 

Please contact us: 

w.k.hensinger@sussex.ac.uk 

More information at: 

http://www.sussex.ac.uk/physics/iqt/ 

There is also a second ion trapping group at 

Sussex: Single-Ion-Cavity-QED group of 

Wolfgang Lange (see poster by Matthias 

Keller and Anders Mortensen).

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