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UNSW 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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UNSW 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 10 8 times faster Spin-off technology development for conventional silicon processing at the sub-1000Å scale

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UNSW

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QUANTUM MECHANICAL COMPUTATION

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UNSW QUANTUM vs CONVENTIONAL COMPUTERS

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UNSW QUANTUM LOGIC Any quantum computation can be reduced to a sequence of 1 and 2 qubit operations: H |in = H 1 H 2 H H n |in Conventional operations: NOT, AND Quantum operations: NOT, CNOT

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UNSW 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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UNSW 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 10 6 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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UNSW In Si:P at Temperature (T)=1K: electron relaxation time = 1 hour nuclear relaxation time = hours

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

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UNSW A & J GATES

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UNSW 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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UNSW

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SPIN READOUT

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UNSW SINGLE ELECTRON TRANSISTORS

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UNSW 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 (0.02 m) feature sizes

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UNSW ELECTRON BEAM LITHOGRAPHY Sub-300Å AuPd gates on GaAs

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UNSW UNSW 3-CHAMBER UHV: STM / AFM, MBE, ANALYSIS

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UNSW STM / AFM AT UNSW 25K K Variable T 3-Chamber UHV Plus: –SiMBE –RHEED –LEED –Auger

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UNSW SRC MANAGEMENT STRUCTURE

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UNSW PROJECT TIMETABLE

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UNSW 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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