THE race to build the world's first quantum computer gained pace this week with the surprise announcement that an Australian group has built the first quantum logic gate to work entirely with light. An unlikely contender until now, the optical technique has suddenly become a leading challenger.
Quantum computers work by exploiting the quantum properties of matter to carry out calculations. Even quite small quantum machines should be able to solve in seconds problems that thwart today's most powerful supercomputers.
But making them work is hugely difficult. A bit of quantum information, a qubit, must be stored and then processed by manipulating its quantum properties. Quantum computation requires two kinds of manipulation. The first, a single-qubit operation, changes a "0" to a "1" by flipping the spin of an atom from one direction to another, or changing the polarisation of a photon, for example. This is relatively straightforward.
The second ...
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