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**FABRICATION OF A NUCLEAR SPIN QUANTUM COMPUTER IN SILICON**

Robert G. Clark Professor of Experimental Physics The University of New South Wales Director National 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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**QUANTUM MECHANICAL COMPUTATION**

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**QUANTUM vs CONVENTIONAL COMPUTERS**

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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 All Problems Factoring CC Quantum Physics Problems NP-Hard Problems? Exhaustive Search

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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. Kane, Nature, May 14, 1998 ~200 Å

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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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**SEMICONDUCTOR NANOFABRICATION FACILITY 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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**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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