Preliminary results indicate that quantum computers are very powerful. They can perform computations which are regarded as intractable on any classical computer. Again the UK has been very active in this area, with major research efforts under way at Oxford , Imperial , Plymouth, Hewlett-Packard Labs and elsewhere. From the fundamental point of view quantum computation allows us to understand better the connections between the laws of physics and processing of information. If practical, quantum computers will outperform classical devices in speed and storage capacity.
Theoretical research shows that quantum computers can for example factor efficiently large integers.
If quantum factorisation can be made practical it will have a significant impact on cryptography. All public key cryptosystems, which are used nowadays to protect and to certify electronic documents, will become vulnerable to quantum cryptoanalytic attacks. Data security will require different cryptosystems. One possibility is quantum cryptography which is needed to provide secure communication, especially when the popular public-key cryptosystems may be broken by quantum computers. A focussed attack on the effects of decoherence on quantum computers is necessary, and quantum error correction codes need to be designed to preserve the quantum information from the deleterious effects of dissipation.