What is Quantum Information?
The applications of quantum mechanics are visible all around us,
most noticeably in semiconductor technology. These are essentially applications
of Schrödinger's equation. For much of the history of quantum mechanics
since the Bohr-Einstein debates there was plenty of philosophical discussion
but little practical application of the more troublesome postulates - the probability
postulate and the collapse of the wave function, and the resulting apparently
paradoxical measurements on entangled states. This has changed in recent years
with a rapid growth of interest in the area known as quantum information. There
are several aspects to this:
Quantum computing If information can be stored in qubits - as the state
of some subsystem - then an n-qubit register can be placed in a linear
superposition of 2n states, and calculations can be performed
on all such numbers simultaneously. In principle this implements massively parallel
computing, exponentially faster than a classical computer. However, a measurement
on the wave function with 2n complex parameters can only extract
n bits, so this may be used only for a restricted class of (nevertheless
highly important) problems. The most famous examples are factorisation (Shor
1994) and database search (Grover 1997). A quantum computer requires well-characterised
qubits, universal quantum gates, a means of initialisation, a means of measurement
of the output and protection against information loss by decoherence. There
are many proposed architectures, but no realistic prototypes.
Quantum communication Quantum mechanics can be used to allow parties
to communicate with complete security. Protocols exist for two parties to agree
on an encryption key by transmitting polarised photons in such a way that any
breach of security will be detectable (as the eavesdropper will collapse the
wave function). A working practical system does exist for this. There are other
related techniques, for example to allow parties to negotiate without divulging
information.
Transparencies of talk on quantum computation
Activities
Quantum Information Processing in Condensed Matter Workshop 15 Sept 2003
Seminar series
Member of EPSRC Network on Transport Dissipation and Control in Quantum Devices
For research projects in this area, see research
page or contact
Dr Dmitry Gulevich
Prof Feodor Kusmartsev
Dr John Samson
Dr Binoy Sobnack
Dr Alexandre Zagoskin
Lectures
PHC130 Fundamentals of Quantum Information
PHD230 Quantum Information and Computing
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