Quantum computers - why would you want one?
Box 1 | Into the nanoworld
Until the microscope was invented 400 years ago, the smallest object our eyes could see was about a tenth of a millimetre across, a speck of dust or a grain of pollen. We did not know anything smaller existed, let alone what it was like.
Since then microscopes, working first with light and later with electrons, have revealed an immense and intricate micro-world. A hundred times smaller than our speck of dust we find living things like bacteria, a few microns (millionths of a metre across), viruses are ten times smaller again, molecules of complex chemicals like DNA are another power of ten down.
As we descend in size, we enter the unsettling nanoworld, where everything is a bit odd. Its inhabitants are uncountable numbers of individual atoms and small molecules of compounds, with sizes of a few nanometres (billionths of a metre) or less. On this scale, a bacterium is huge, a vast blimp more than thousand nanometres across. Even a passing virus would block out the Sun.
The way of life is very different down here. Quantum physics rules. In our everyday world, we can measure with precision both where something is and how fast it is going. Not so in the nanoworld. It is all fuzzy. The more you know about the speed of an atom, the less you know about its location. The more precise you are about when an event takes place, the more uncertain will be your measurement of any associated energy. It sounds crazy, but that is how things are.
This inescapable uncertainty poses real problems for visitors from above. We have no trouble up here making the stream of electrons that constitute an electric current stay inside the wire carrying it. But as quantum uncertainties begin to intrude, we grow less certain about just where the electrons are. Are they inside the wire or outside? This means that electric charge can leak easily from nanosize boxes, whereas the micron-size ones on a computer chip hold such charges securely.
Boxes
Box 2. What are we up to here in Australia?
Box 3. So when will we have one?
Related sites
'Exact uncertainty' brought to quantum world (New Scientist, 27 April 2002)
Nanoscience – working small, thinking big (Nova: Science in the news, Australian Academy of Science)
Posted August 2007.