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**A NUCLEAR SPIN QUANTUM COMPUTER IN SILICON**

Microanalytical Research Centre M A R C A NUCLEAR SPIN QUANTUM COMPUTER IN 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 world’s 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 |in> = H1 H2 H Hn |in> Conventional operations: NOT, AND Quantum operations: NOT, CNOT

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QUANTUM ALGORITHMS Superposition and entanglement enables massive parallel processing Shor’s prime factorization algorithm (1994) relevant to cryptography Grover’s exhaustive search algorithm (1996) QC CC Factoring Quantum Physics Problems Exhaustive Search NP-Hard Problems? All Problems

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**EXPERIMENTAL QUANTUM COMPUTATION**

Bulk spin resonance (Stanford, MIT): ? qubits Trapped cooled ions (Los Alamos, Oxford): ? 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/

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**In Si:P at Temperature (T)=1K:**

electron relaxation time = 1 hour nuclear relaxation time = hours

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**A Silicon-based nuclear spin quantum computer B. E**

A Silicon-based nuclear spin quantum computer B. E. Kane, Nature, May 14, 1998 ~200 Å

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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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SPIN READOUT

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**SINGLE ELECTRON TRANSISTORS**

SPIN READOUT

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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 K 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 Academic Staff Geoff Leech* DeborahLouGreig**

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

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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**

Scale bars: 1 mm intervals Heavy ion etch pit Light ion etch pits 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 1. Irradiate 2. Latent damage 3. Etch From: B.E. Fischer, Nucl. Instr. Meth. B54 (1991) 401.

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Single ion tracks Latent damage from single-ion irradiation of a crystal (Bi2Sr2CaCuOx) Beam: 230 MeV Au Lighter ions produce narrower tracks! Depth 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 Readout Theory/Modelling Array fabrication SET Dzurak Magnetic Resonance (LANL) Quantum Optics Rubeinstein-Dunlop Single Ion Implantation Jamieson Atom Lithography Prawer Silicon MBE Simmons

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