A role for ion implantation in quantum computing David N. Jamieson * , Steven Prawer, Igor Andrienko, David A. Brett, Victoria Millar Special Research Centre for Quantum Computer Technology and The Microanalytical Research Centre, School of Physics, The University of Melbourne, Parkville, Vic. 3010, Australia Abstract We propose to create arrays of phosphorus atoms in silicon for quantum computing using ion implantation. Since the implantation of the ions is essentially random, the yield of usefully spaced atoms is low and therefore some method of registering the passage of a single ion is required. This can be accomplished by implantation of the ions through a thin surface layer consisting of resist. Changes to the chemical and/or electrical properties of the resist will be used to mark the site of the buried ion. For chemical changes, the latent damage will be developed and the atomic force mi- croscope AFM) used to image the changes in topography. Alternatively, changes in electrical properties which obviate the need for post-irradiation chemical etching) will be used to register the passage of the ion using scanning tunneling microscopy STM), the surface current imaging mode of the AFM. We address the central issue of the contrast created by the passage of a single ion through resist layers of PMMA and C 60 . Ó 2001 Elsevier Science B.V. All rights reserved. PACS: 03.67.Lx; 85.40.Ry; 61.72.Ff; 61.72.Tt; 61.80.Jh; 61.82.Pv; 81.05.Tp Keywords: Kane quantum computer; Single ion irradiation; Ion tracks; Ion irradiation of fullerene; Ion irradiation of PMMA resist 1. Introduction Over the past 30 years, continued increase in computer power has occurred as the dimensions of individual devices on computer chips have become smaller with each new model a trend known as Moore's law). There is some evidence that this trend is now slackening and indeed it cannot continue inde®nitely as ultimately device size will shrink until the number of electrons in each device is too small for stable operation. Hence if com- puter power is to continue to increase, a new paradigm for computation is required. One of the most promising avenues is to take advantage of the rules of quantum mechanics to construct a massively parallel quantum computer. The quantum computer promises remarkable advances in computational power for certain problems that are impractical on classical com- puters. In a quantum computer individual bits, known as qubits, exist in entangled states allowing all possible states of the computer to exist simul- taneously. A qubit is a quantum entity that can exist in a superimposed state consisting of two Nuclear Instruments and Methods in Physics Research B 175±177 2001) 744±750 www.elsevier.nl/locate/nimb * Corresponding author. Tel.: + 61-3-8344-5376; fax: + 61-3- 9347-4783. E-mail address: dnj@physics.unimelb.edu.au D.N. Jamie- son). 0168-583X/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X  0 0 ) 0 0 6 8 0 - 7