A NUCLEAR SPIN QUANTUM COMPUTER IN SILICON

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A NUCLEAR SPINQUANTUM COMPUTERIN SILICON

• National Nanofabrication Laboratory, School of
  Physics, University of New South Wales
• Laser Physics Centre, Department of Physics,
  University of Queensland
• Microanalytical Research Centre, School of
  Physics, University of Melbourne

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Key Personnel

• Students
• Paul Otsuka
• MatthewNorman
• Elizabeth Trajkov
• Brett Johnson
• Amelia Liu
• Leigh Morpheth
• David Hoxley
• Andrew Bettiol
• Deborah Beckman
• Jacinta Den Besten
• Kristie Kerr
• Louie Kostidis
• Poo Fun Lai
• Jamie Laird
• Kin Kiong Lee

• Geoff Leech DeborahLouGreig
• Ming Sheng Liu
• Glenn Moloney
• Julius Orwa
• Arthur Sakalleiou
• Russell Walker
• Cameron Wellard

• Academic Staff
• David Jamieson
• Steven Prawer
• Lloyd Hollenberg
• Postdoctoral Fellows
• Jeff McCallum
• Paul Spizzirri
• Igor Adrienko
• 2
• Infrastructure
• Alberto Cimmino
• Roland Szymanski
• William Belcher
• Eliecer Para

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The Quantum Computer Melbourne Node
Node Team Leader Steven Prawer
Test structures created by single ion implantation
Atom Lithography and AFM measurement of test
structures
Theory of Coherence and Decoherence
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Fabrication Pathways

• Fabrication strategies
• (1) Nano-scale lithography
• Atom-scale lithography using STM H-resist
• MBE growth
• EBL patterning of A, J-Gates
• EBL patterning of SETs
• (2) Direct 31P ion implantation
• Spin measurement by SETs or magnetic resonance
  force microscopy
• Major collaboration with Los Alamos National
  Laboratory, funded through US National Security
  Agency

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keV electrons and MeV ions interact with matter

• Restricted to 10 ?m depth, large straggling
• Low beam damage

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The Melbourne Pelletron Accelerator

• Installed in 1975 for nuclear physics
  experiments.
• National Electrostatics Corp. 5U Pelletron.
• Now full time for nuclear microprobe operation.
• Will be state-of-the-art following RIEFP upgrade

Inside
Outside
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Nuclear microprobe essential components
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Chamber inside

• 30 mm2 Si(Li) x-ray detector
• 25 and 100 msr PIPS particle detectors at 150o
• 75 msr annular detector

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MeV ions interact with matter
3 MeV H

• MeV ions penetrate deeply without scattering
  except at end of range.
• Energy loss is first by electronic stopping
• Then nuclear interactions at end of range

PMMA substrate(side view)
surface
100 ?m
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Micomachining
Protons

• Example
• Proton beam lithography
• PolyMethyl MethAcrylate (PMMA)
• exposure followed by development
• 2 MeV protons
• clearly shows lateral straggling

10 ?m
Side view
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MeV ion beam micromachiningHigh aspect ratio
structures in PMMA
The work of Frank Watt
Work done at the Nuclear Microscopy Unit at the
National University of Singapore

• 2.3 MeV protons on PMMA
• This work dates from 1996, much more interesting
  structures are now available
• See review by Prof F. Watt, ICNMTA6 - Cape Town,
  October 1998

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MeV ion beam micromachiningOptical Materials
The work of Mark von Bibra

• Fused Silica
• Increase in density at end of range
• Increase in refractive index (up to 2) at end of
  range

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MeV ion beam micromachiningLayered Waveguides
The work of Mark von Bibra

• Ion energy ---- waveguide depth

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Single Ion Implantation Fabrication Strategy
Etch latent damage metallise
Read-out state of qubits
MeV 31P implant
Resist layer
Si substrate
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MeV ion etch pits in track detector

• Single MeV heavy ions are used to produce latent
  damage in plastic
• Etching in NaOH develops this damage to produce
  pits
• Light ions produce smaller pits

3. Etch
2. Latent damage
1. Irradiate
From B.E. Fischer, Nucl. Instr. Meth. B54 (1991)
401.
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Single ion tracks
Depth

• Latent damage from single-ion irradiation of a
  crystal (Bi2Sr2CaCuOx)
• Beam 230 MeV Au
• Lighter ions produce narrower tracks!

1 mm
3 mm
5 mm
7.5 mm
3 nm
From Huang and Sasaki, Influence of ion velocity
on damage efficiency in the single ion target
irradiation system Au-Bi2Sr2CaCu2Ox Phys Rev B
59, p3862
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High energy single-ion tracks in silicon direct
imaging with scanning probe microscopy

• Nanofabrication by the implantation of MeV
  single-ions offers a novel method for the
  construction of small devices which we call
  atomic-lithography. A leading contender for the
  first nano-device constructed by this method is
  an array of spins for a quantum computer. For
  the first time, we propose the use of high
  resolution scanning probe microscopy (SPM) to
  directly image irradiation-induced machining
  along the ion track and lattice location of the
  implanted ion in silicon on an atomic scale.
  This will allow us to measure the spatial
  distribution of defects and donors along the
  tracks to analyse the atom-scale electronic
  properties of the irradiated materials.

STM/AFM tip
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Spin array test structure

• Aim Create a spin array for test imaging with
  MRAFM

Grid
ltSigt
Implant 31P through mask of 1 micron period
grid 300 nm deep (220 keV 31P)
Resulting array of 1 micron islands of
spins Number of spins in each island is 1x10-8?D,
D is 31P dose in P/cm2