A couple of journalists have recently asked me some questions about the EPSRC Ideas Factory on software control of matter that I am directing in January. The obvious question is whether software control of matter – which was defined as “a device or scheme that can arrange atoms or molecules according to an arbitrary, user-defined blueprint” – will be possible. I don’t know the answer to this – in some very limited sense (for example, the self-assembly of nanostructures based on DNA molecules with specified sequences) it is possible now, but whether these very tentative steps can be fully generalised is not yet clear (and if it was clear, then there would be no point in having the Ideas Factory). More interesting, perhaps is the question of what one would do with such a technology if one had it. Would it lead to, for example, the full MNT vision of Drexler, with personal nanofactories based on the principles of mechanical engineering executed with truly atomic precision?
I don’t think so. I’ve written before of the difficulties that this project would face, and I don’t want to repeat that argument here. Instead, I want to argue that this mechanically focused vision of nanotechnology actually misses the biggest opportunity that this level of control over matter would offer – the possibility of precisely controlling the interactions between electrons and light within matter. The key idea here is that of the “metamaterial”, but the potential goes much further than simply designing materials: instead, the prize is the complete erosion of the distinction we have now between a “material” and a “device”.
A “metamaterial” is the name given to a nanoscale arrangement of atoms that gives rise to new electronic,magnetic or optical properties that would not be obtainable in a single, homogenous material. It’s been known for some time, for example, that structures of alternating layers of different semiconductors can behave, as far as an electron is concerned, as a new material with entirely new semiconducting properties. The confinement of electrons in “quantum dots” – nanoscale particles of semiconductors – profoundly changes the quantum states allowed to an electron, and clever combinations of quantum dots and layered structures yield novel lasers now, and the promise of quantum information processing devices in the future. For light, the natural gemstone opal – formed by the self-assembly of spherical particles in ordered arrays – offers a prototype for metamaterials that interact with light in interesting and useful ways. This field has been recently energised by the theoretical work of John Pendry, , at Imperial College, who has demonstrated that in principle arrays of patterned dielectrics and conductors can behave as materials with a negative refractive index.
This notion of optical metamaterials has achieved media notoriety as a route to making “invisibility cloaks” (see this review in Science for a more sober assessment). But the importance of these materials is much more general than that – in principle, if one can arrange the components of the metamaterial with nanoscale precision to some pattern that one calculates, one can guide light to go pretty much anywhere. If you combine this with the ability from semiconductor nanotechnology to manipulate electronic states, and from magnetic nanotechnology to manipulate electron spin, one has the potential for an integrated information technology of huge power. This will probably use not just the charge of the electron, as is done now, but its spin (spintronics) and/or its quantum state (quantum computing). There are, of course, some big ifs here, and I’m far from being confident that the required degree of generality, precision and control is possible. But I am sure that if something like a “matter compiler” is possible, it is manipulating photons and electrons, rather than carrying out fundamentally mechanical operations, that its products will be used for.