If I have seen further it is by standing on the shoulders of giants.

Monday, December 12, 2011

Lectures on Quantum Computation | David Deutsch

DAVID DEUTSCH is the founder of the field of quantum computation. Paul Benioff, Richard Feynman, and others had written about the possibility of quantum computation earlier, but Deutsch's 1985 paper on Quantum Turing Machines was the first full treatment of the subject, and the Deutsch-Jozsa algorithm is the first quantum algorithm.

When he first proposed it, quantum computation seemed practically impossible. But the last decade has seen an explosion in the construction of simple quantum computers and quantum communication systems. None of this would have taken place without Deutsch's work.

The main papers written by Deutsch that contained "achievement in scientific work that embodies extensions of the computational idea" were in 1985 ("Quantum theory, the Church-Turing principle, and the universal quantum computer") and 1989 ("Quantum computational networks").

His 1995 paper, "Conditional quantum dynamics and logic gates" (with A. Barenco, A. Ekert and R. Jozsa) was an important step in clarifying what sort of physical processes would be needed to implement quantum computation in the laboratory, and what sort of things the experimentalists should be trying to get to work.

"Universality in quantum computation", also written in 1995 (with A. Barenco and A. Ekert) proved the universality of almost all 2-qubit quantum gates, thus verifying his conjecture made in 1989 and showing that quantum computation and quantum gate operations are 'built in' to quantum physics far more deeply than classical physics. In 1996, in "Quantum privacy amplification and the security of quantum cryptography over noisy channels" (with A. Ekert, R. Jozsa, C. Macchiavello, S. Popescu and A. Sanpera), he brought quantum cryptography a little bit closer to being practical as opposed to just a laboratory curiosity.

His recent work as seen in the following three papers can be seen as new "applications" of the computational idea, rather than extensions of it.

In 2000, "Information Flow in Entangled Quantum Systems" (with P. Hayden) refutes the long-held belief that quantum systems contain 'non-local' effects, and it does it by appealing to the universality of quantum computational networks, and analysing information flow in those.

Also in 2000, in "Machines, Logic and Quantum Physics" (with A. Ekert and R. Lupacchini), a philosophic paper, not a scientific one, he appealed to the existence of a distinctive quantum theory of computation to argue that our knowledge of mathematics is derived from, and is subordinate to, our knowledge of physics (even though mathematical truth is independent of physics).

In 2002, he answered several long-standing questions about the multiverse interpretation of quantum theory in "The Structure of the Multiverse" — in particular, what sort of structure a 'universe' is, within the multiverse. It does this by using the methods of the quantum theory of computation to analyse information flow in the multiverse.

His two main lines of research at the moment, Qubit Field Theory and quantum constructor theory, may well yield important extensions of the computational idea eventually, but at the moment neither of them has yielded any results at all, to speak of, only promising avenues of research.

Born in Haifa, Israel, David Deutsch was educated at Cambridge and Oxford universities. After several years at the University of Texas at Austin, he returned to Oxford, where he now lives and works. Since 1999, he has been a non-stipendiary Visiting Professor of Physics at the University of Oxford, where he is a member of the Centre for Quantum Computation at the Clarendon Laboratory, Oxford University.

In 1998 he was awarded the Institute of Physics' Paul Dirac Prize and Medal. This is the Premier Award for theoretical physics within the gift of the Council of the Institute of Physics. It is made for “outstanding contributions to theoretical (including mathematical and computational) physics”. In 2002 he received the Fourth International Award on Quantum Communication for “theoretical work on Quantum Computer Science”.

In the Royal Society of London's announcement of Deutsch becoming a Fellow of the Royal Society (FRS) in 2008, the Society described Deutsch's contributions thus:

David Deutsch laid the foundations of the quantum theory of computation, and has subsequently made or participated in many of the most important advances in the field, including the discovery of the first quantum algorithms, the theory of quantum logic gates and quantum computational networks, the first quantum error-correction scheme, and several fundamental quantum universality results. He has set the agenda for worldwide research efforts in this new, interdisciplinary field, made progress in understanding its philosophical implications (via a variant of the many-universes interpretation) and made it comprehensible to the general public, notably in his book The Fabric of Reality.

Lecture 1 - The Qubit [Worked Examples]

Introducing quantum theory, the quantum theory of computation, physical systems, observations, and the simplest quantum physical system, the qubit.

David Deutsch - Quantum Computation Lecture 1 - wmv

Lecture 2 - Interference [Worked Examples]

Performing and analysing a single-photon interference experiment.

David Deutsch - Quantum Computation Lecture 2 - wmv

Lecture 3 - Measurement [Worked Examples]

How to analyse pairs of interacting quantum systems.

David Deutsch - Quantum Computation Lecture 3 - wmv

Lecture 4 - The Schroedinger Picture

Introducing the Schroedinger Picture, density matrices, state vectors, pure states and the Schroedinger equation.

David Deutsch - Quantum Computation Lecture 4 - wmv

Lecture 5 - A Quantum Algorithm

The Deutsch Algorithm and how it works.

David Deutsch - Quantum Computation Lecture 5 - wmv

Lecture 6 - Grover's Search Algorithm

How to use quantum computation to search through N possibilities in a time proportional to the square root of N.

David Deutsch - Quantum Computation Lecture 6 - wmv

See also: Interview with David Deutsch - It's a much bigger than it looks

Quantiki | Quantum Information Portal
David Deutsch's Site | Old Site

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