Where nanotechnology meets

The STM has

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comwtation by Evaristus Mainsah

ince the invention of the scanning tunnelling microscope (STM) in the early 1980s atonuc level microscopy bas taken on a new S dimension’. The STM and thc atomic forcc

microscope (AFM) have become key instruments in the study of phenomena in the smallest dimensions ranging from magnetism in ultra-thin films, through the understanding of how atoms and molecules organise themselves, to insights into the propagation of electron waves. A good understanding of these issues will facilitate the manufactore of components or devices that are a few atonic dimensions in size and this wdl have far-reachng implications in fields ranging Gom medicine through to constinier electronics.

Richard Fcynman’s vision ofa world with computers and machines designed and built in the nanonietre scale might in 1959 have appeared far-fetched, but advances since then have substantiated his belief that ’... the principles ofphysics do nor speak against the possibility

become a useful and routine tool for observing and manipulating atoms and has resulted in some amzing insights into nanotechnology

Notwithstanding the advances achieved since then, few devices of the type envisaged by Feynnman are in use, but the prospects are better than ever before. Whilst there has been discussion ofthe possible medical benefits of devices so small that they can be used to deliver localised treatment (for exaniple to cancer cells) by sailing in the blood-stream, recent work by Kawata and colleaguesi demonstrates that we may be very close, perhaps only a generation away Using the two- photon photopolymerisation technique that they had previously developed, they have managed to create a ‘micro-bull’ sculpture (Fig. 1) --a three-dimensional

the nvisting form of a bull 7 pin high by piece of

Fig. 1 ’Micro-bull‘ sculpture produced by Kawata eta/.’

10 pi loilg-the size of a red blood cell. Although it has no moving parts, this demonstrates that it is now possible to make intricate shapes in the nanotechnology scale-a prerequisite for pervasive nano- technology

Moving parts will require further advances in microrlectroniechanical devices. There has been some suggestion that nanotubes may provide the answer and recently Zett14 was able to create ultra-thin frictionless bearings (Fig. 2) and springs by manipulating nanorubes. These could form the basis of exceptionally fast switches.

These are only nvo examples in a wealth of significant steps that have been taken towards the realisation of FcynnianS vision. Progress has been made in both manu- facturing paradigms: bottom-up, where the device is constructed from molecules; and top-down, through etching or machining Goni bulk materials.

In computing there is already concern

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about how much longer Moore's law, i.e. the doubling of computing power in about 18 months, can continue to hold fast. I t is clear that device miniaturisation can continue for only a few more generations before quantum effects make it very hard to build circuits that behave like reliable classical switches. As early as the 1970s, the scientific conununity was discussing the possibility of enibedding a few molecules, or even a single molecule, between electrodes to perform the basic switching function. This is now possible in the case ofindividual components but key challenges lie with the rconomic conmcrcial fabrication of whole devices. Approaches based on mono-molecular electronics-using single molecules for both the elementary functions and interconnections-have shown some promisei. I n fact, Derycke and colleagues at the IBM T. J. Watson Research Center havejust reported what they claim to be the smallest-ever computer logic circuit, a two- transistor coinponrnt made from a single molecule of carbon in the form of a nanotubr6. This br ing closer the goal of creating microprocessors using nanotube technology resultingin smaller, faster and more energy efficient computers.

In the quantum computingworld, data can be stored in the quantum states ofan atom-capable ofstoring not just a '0' or a '1' but, through superposition, both a '0' and a '1' at thr sa~iie time (with a certain probabhty). These qubits (quantuni bits) were for a few years niore of a curiosity but when Shor' demonstrated that the factorisation of large numbers (normally carried out in polynomial time on a classical computer) can be achieved iiiore rapidly using a quantum coniputer (thereby making the world's encryption algorithms not so much bullet-proof as wafer-thin), efforts to create a quantum computer redoubled. A quick search of the bibliography would contimi that quantum computing has now conic of age8.

While problems of uoise and reliability clearly get worse, dstinctively quantum effecrs appear that can be harnessed to achieve qualitatively new kinds of information processing. For example, if messages arc sent with individual photons, message privacy and encryption become. easier rather than harder, based now on basic laws of quantum physics rather than on mathematical assumptions. A key challenge lies in determining whether such quantum computers will work and how quantum effects can be used to perform a variety of previously unsuspected and potentially useful schemes of information processing, including quantum cryptography, quantum teleportation and quantum error-correcting codri'.

Quantum computation is clearly the science of the 21st century; there is no con~ensus on when nanotechnological devices will become pervasive, but it is clear that the search demands that experts in fields such as molecular biology, physics, electronics, quantum computation and nanotechnoloby leverage gains made in the different discipliues.

" on Foundations of Computer Sciencc, 1994, pp.124-134

8 UOLNIIMEESTEK, U, EKERT, A,, and ZEILINGER, A. (Edi.): 'The Dhviici of oiiantum information' (Sorinecr. . , , 1 L_ . . Berlin, 2000)

Y BENNETT, C. H., and IIIVINCENZO, D. P: ' Q u a n t ~ n i information and compotation', .N"P, 2000, 404, pp.247-275

OIEE: 2001, 2002

The above article first appeared as the editorial accompanying a ipecial section on 'Nanotechnolopv and quantum computing' published in IEE Prmedir,,p S&we, Mmsrrrurrwii arid Ikli,iuiogy in September 2001

Dr. Mainsah is with the Software Gmup of IUM UK Ltd.. MP104, Hurrlry Park, Winchcrier SO21 2JN, UK. E-,mi/: Mainsah@uk.ibm.corr,

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