futures Programmable matter How quantum wellstone ushered in our modern age

can trap conduction electrons in a mem- threads much thinner than a human hair, Wil McCarthy brane so thin that from one face to the other, crisscrossing to form a translucent structure their behaviour as tiny quantum wave pack- with roughly the density of balsa wood. Like July 2100. The flick of a switch: a wall ets takes precedence over their behaviour as balsa wood, the structure consists mostly of becomes a window becomes a door. particles. This is called a ‘quantum well.’ empty space, except that with the application 4Any chair becomes a hypercomputer, From there, confining the electrons along a of electrical currents, that space can be filled any rooftop a power- or waste-treatment second dimension produces a ‘quantum with ‘atoms’ of any desired species, produc- plant. We scarcely notice; programmable wire’, and finally, with three dimensions, a ing a virtual substance with the mass of dif- matter pervades our homes, our work- ‘quantum dot’. fuse silicon, but the chemical, physical, and places, our vehicles and environments. The unique trait of a quantum dot, as electrical properties of some new, hybrid There isn’t a city on Earth — or Mars, for opposed to any other electronic component, material. that matter — that isn’t clothed in the stuff is that the electrons trapped in it will arrange Wellstone iron is weaker than its natural from rooftop to sub-basement. But though themselves as though they were part of an counterpart, less conductive and ferromag- we rarely stop to consider it, the bones of atom, even though there’s no atomic nucleus netic — essentially, less ‘iron-like’ — and if these cities — their streets, their sewers, the for them to surround. Which atom they you bash it over and over with a golf club it hearts of their telecom networks — were emulate depends on the number of electrons will gradually lose any resemblance to iron, laid out in a time when the properties of and the exact geometry of the wells that con- reverting to shattered silicon and empty matter were dictated exclusively by mother fine them, and in fact where a normal atom is space. On the other hand, it’s feather-light, nature. spherical, such ‘designer atoms’ can be wholly rustproof, and changeable at the flick Imagine: if specific mechanical or electri- turned into cubes, tetrahedra or any other of a bit into zinc, rubidium, or even imagi- cal properties were desired, one first had to shape, and filled with vastly more electrons nary substances like impervium, the tough- hire miners to extract appropriate elements than any real nucleus could support, to pro- est superreflector known. from the Earth, then chemists and metallur- duce ‘atoms’ with properties that simply Of the changes wrought by programma- gists to mix precise proportions under pre- don’t occur in nature. ble matter in the past century, not all have cise conditions, then artisans to craft the Significantly, the quantum dots needn’t been universally welcomed. Wellstone, in the resulting materials into components, and be part of the physical structure of the semi- grand Promethean tradition, places the assemble the components into products that conductor; they can be maintained just power of creation and destruction squarely could then be transported to the location of above it through a careful balancing of elec- into human hands. Many have argued that, desired use. The inconvenience must have trical charges. In fact, this is the preferred far from making us strong, this power fosters been staggering. method, since it permits the dots’ character- a quiet corruption of spirit. Still, the fable of In the 22nd century, of course, any com- istics to be adjusted without any physical the three little pigs holds true — not even the petent designer will simply define the shape modification of the substrate. Luddites among us build their houses of and properties they require, including Who invented wellstone remains a matter straw or sticks, when impervium is a free ‘unnatural’ traits such as superreflectance, of debate: similar work was being performed download. refraction matching (invisibility), and cen- in parallel, in laboratories all over the world. Wil McCarthy, an aerospace engineer and tuple bonds far stronger than diamond, then Regardless of whose actual idea it was, the science columnist, is the author of six science distribute the configuration file to any inter- concept itself is deceptively simple: a diffuse fiction novels, including Bloom (Millennium) ested users. But prior to the invention of lattice of crystalline silicon, superfine and The Collapsium (Del Rey/Gollancz). wellstone — the earliest form of program- mable matter — this would have been pure

fantasy. With this in mind, we’ll look back on JACEY the invention upon which, arguably, our entire civilization rests. Consider silicon, whose oxide is the most abundant material on Earth. Humans had been making hammers and millstones out of it for millions of years, but as it happens, sili- con is also a semiconductor. The electrical properties of pure silicon are fixed by the laws of physics, but through doping — the care- fully controlled introduction of impurities — its crystals can be tuned so that, for exam- ple, room-temperature electrons have a good chance of jumping up into the conduc- tion band. While invaluable in the development of twentieth-century digital electronics, sili- con’s killer application eventually proved to be as a storage medium for electrons. The layering of doped silica in particular ways

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