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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MOTIVATION

• Quantum Computers will be the worlds fastest
  computing devices, e.g. decryption (prime factors
  of a composite number)- Factor a 400 digit
  number 108 times faster
• Spin-off technology development for conventional
  silicon processing at the sub-1000Å scale

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QUANTUM MECHANICAL COMPUTATION
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QUANTUM LOGIC

• Any quantum computation can be reduced to a
  sequence of 1 and 2 qubit operations
• H ingt H1 H2 H3 .... Hn ingt
• Conventional operations NOT, AND
  Quantum operations NOT, CNOT

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QUANTUM ALGORITHMS

• Superposition and entanglement enables massive
  parallel processing
• Shors prime factorization algorithm (1994)
  relevant to cryptography
• Grovers exhaustive search algorithm (1996)

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EXPERIMENTAL QUANTUM COMPUTATION

• Bulk spin resonance (Stanford, MIT) 1-10?
  qubits
• Trapped cooled ions (Los Alamos, Oxford)
  1-100? qubits
• True quantum computer may require 106 qubits
• Solid state (semiconductor) quantum computer
  architectures
• Proposed using electron and nuclear spin to store
  qubits
• Electrons D. Loss and D. DiVincenzo, Phys. Rev.
  A 57, 120 (1998).
• Nuclei V. Privman, I. D. Vagner, and G.
  Kventsel, Phys. Lett. A in press,
  quant-ph/9707017.

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In SiP at Temperature (T)1K electron
relaxation time 1 hour nuclear relaxation time
1013 hours
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A Silicon-based nuclear spin quantum computerB.
E. Kane, Nature, May 14, 1998
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A J GATES
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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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(1) Nano-scale Lithography
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SINGLE ELECTRON TRANSISTORS
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ELECTRON BEAM LITHOGRAPHY
Sub-300Å AuPd gates on GaAs
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UNSW 3-CHAMBER UHV STM / AFM, MBE, ANALYSIS

• 25K - 1500K Variable T
• 3-Chamber UHV
• Plus Si-MBE, RHEED, LEED, Auger

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SRC MANAGEMENT STRUCTURE
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PROJECT TIMETABLE
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SUMMARY

• Quantum Computers have enormous potential
• Solid-state quantum computation is the best
  candidate for scalability
• Offers integration with existing Si technology
• UNSW strategy to use qubits stored on nuclear
  spins (concept by Kane)

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The 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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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
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• Infrastructure
• Alberto Cimmino
• Roland Szymanski
• William Belcher
• Eliecer Para

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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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Project Management - A distributed system
Director Clark
Deputy Director Milburn
Theory/Modelling
Array fabrication
Readout
SET Dzurak
Magnetic Resonance (LANL)
Quantum Optics Rubeinstein-Dunlop
Single Ion Implantation Jamieson
Atom Lithography Prawer
Silicon MBE Simmons