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FABRICATION OF A NUCLEAR SPINQUANTUM COMPUTER IN SILICON

Robert G. Clark

Professor of Experimental PhysicsThe University of New South Wales

DirectorNational Magnet Laboratory and

Semiconductor Naofabrication Facility

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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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Caltech-MRFM

LANL-MRFM-STM-Theory-Ion Trap QC-NMR QC

UNSW-STM -EBL-MBE -SETTs-Nanostructures

U Maryland-Single spin

detection

UQ

-Theory/Modelling-Quantum Optics

U Melbourne(ANU)

-STM-Ion Implantation ARC

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USNSA

USA COLLABORATIONS

CENTRE FOR QUANTUM COMPUTER TECHNOLOGYAUSTRALIA

LANL $

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QUANTUM MECHANICAL COMPUTATION

Conventional Quantum Computer Computer

0,1 |0|1

Bits "Qubits"

Quantum state of a two-level system such as spin 1/2

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QUANTUM vs CONVENTIONAL COMPUTERS

1. Superposition: ||0|1

2. Entanglement: ||01 |10

3. Quantum computation must be reversible:

H |in|out; H –1 |out|in

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NOT CONTROLLED NOT IN OUT IN OUT|0|1 |00|00|1|0 |01|01 |10|11 |11|10

+Phase shifts

QUANTUM LOGICAny quantum computation can be reduced to a sequence of 1 and 2 qubit operations:

H |in= H1 H2 H3 .... 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

CCFactoring

Quantum Physics Problems

Exhaustive SearchNP-HardProblems?

All Problems

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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 qubitsElectrons: 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 Si:P at Temperature (T)=1K:

electron relaxation time = 1 hour

nuclear relaxation time = 1013 hours

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~200 Å

“A Silicon-based nuclear spinquantum computer”

B. E. Kane, Nature, May 14, 1998

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A & J GATES

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• Fabrication strategy involves:– Atom-scale lithography using STM H-resist

– MBE growth

– EBL patterning of A, J-Gates

– EBL patterning of SETs

• 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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SPIN READOUT

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SINGLE ELECTRON TRANSISTORS

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SEMICONDUCTORNANOFABRICATIONFACILITY

• Established 1995

• Consortium of major Universities in the Sydney area

• Physics, Engineering Research Team

• GaAs nanostructures Si - Quantum wire transistors

• 200 Å (0.02m) feature sizes

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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

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STM / AFM AT UNSW

• 25K - 1500K Variable T• 3-Chamber UHV• Plus:

– SiMBE

– RHEED

– LEED

– Auger

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STEERING COMMITTEE

- Financial & Capital Management- Meets Quarterly

SRC EXECUTIVE

Director: Prof. ClarkDep. Dir: Prof. Milburn

INTERNATIONAL ADVISORY BOARD

- R&D, Commercial Strategy- Meets Half-yearly

AUSTRALIAN PROJECT MANAGEMENT - Meet Monthly (Teleconference) US PROJECT MANAGEMENT

Clark Dzurak Milburn / White Honsberg Prawer / Jamieson Simmons

Hammel (LANL) Kane (Maryland) Hughes (LANL) Roukes (Caltech)

Steering Committee Prof. C. Fell Deputy VC (Research), UNSW Prof. P. Greenfield Deputy VC (Research),

Univ. of Queensland Prof. F. Larkins Deputy VC (Research),

Univ. of Melbourne Prof. R. Clark Director SRC Prof. G. Milburn Deputy Director SRC A/Prof. S. Prawer Univ. of Melbourne Dr. P. Hammel LANL Representative Dr. P. Szczepanek NSA Representative

* or their delegated representatives

International Advisory Board Dr. B. Press* Deputy Director (S&T Programs), LANL, USA Dr. K. Miller* Quantum Computing Research Coordinator,

US National Security Agency Prof. C. Fell Deputy Vice Chancellor (Research), UNSW Prof. P. Greenfield Deputy Vice Chancellor (Research),

Univ. of Queensland Prof. F. Larkins Deputy Vice Chancellor (Research),

Univ. of Melbourne Dr. S. Williams Hewlett Packard, Palo Alto, USA Dr. D. Bolt Intel Australia Ltd. Dr. A. Ekert Clarendon Laboratory, Univ. of Oxford Prof. M. Pepper Univ. of Cambridge, UK &

Director, Toshiba Research Centre, UK Prof. M. Skeats CEO Australian Photonics CRC, &

Exec. Dir. of Australian Photonics P/L

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)