Professor Artur Ekert FRS

Abstract:

We discuss possibilities of protecting quantum states against disturbances introduced by quantum measurements. We specify conditions under which it is possible to restore an unknown state of a combined quantum system after measurements which were performed on some (but not on all) of its components.

Abstract:

We propose a method for the stabilization of quantum computations (including quantum state storage). The method is based on the operation of projection into SYM, the symmetric subspace of the full state space of R redundant copies of the computer. We describe an efficient algorithm and quantum network effecting SYM-projection and discuss the stabilizing effect of the proposed method in the context of unitary errors generated by hardware imprecision, and nonunitary errors arising from external environmental interaction. Finally, limitations of the method are discussed.

Abstract:

We describe how physics of computation determines computational complexity. In particular we show how quantum phenomena lead to qualitatively new modes of computation. An ideal quantum computer would allow to face certain tasks out of reach of classical computers, the factorization problem being the most striking example. Experimentally, however, implementation of quantum computation faces some serious difficulties due to an interaction with the environment which causes decoherence. We mention quantum error-correction as a process which can, to some extent, protect quantum computers from unwelcome effects of dissipation and decoherence. This is a brief, introductory review of quantum computation. It is based on [1].