[extropy-chat] Deutsch: Universal Quantum Computers are Only Years Away

[Giu1i0 Pri5c0]

On David Deutsch's
blog<http://www.qubit.org/people/david/index.php?path=Weblog>:
For a long time my standard answer to the question 'how long will it be 
before the first universal quantum computer is built?' was 'several decades 
at least'. In fact, I have been saying this for almost exactly two decades … 
and now I am pleased to report that recent theoretical advances have caused 
me to conclude that we are within sight of that goal. It may well be 
achieved within the next decade. The main discovery that has made the 
difference is cluster quantum
computation<http://xxx.lanl.gov/abs/quant-ph/0508218>,
which is a marvellous new way of structuring quantum computations which 
makes them far, far easier to implement physically.
Abstract of the article on cluster quantum
computation<http://xxx.lanl.gov/abs/quant-ph/0508218>:
We introduce an architecture for robust and scalable quantum computation 
using both stationary qubits (e.g. single photon sources made out of trapped 
atoms, molecules, ions, quantum dots, or defect centers in solids) and 
flying qubits (e.g. photons). Our scheme solves some of the most pressing 
problems in existing non-hybrid proposals, which include the difficulty of 
scaling conventional stationary qubit approaches, and the lack of practical 
means for storing single photons in linear optics setups. We combine 
elements of two previous proposals for distributed quantum computing, namely 
the efficient photon-loss tolerant build up of cluster states by Barrett and 
Kok [Phys. Rev. A 71, 060310 (2005)] with the idea of Repeat-Until-Success 
(RUS) quantum computing by Lim et al. [Phys. Rev. Lett. 95, 030505 (2005)]. 
This idea can be used to perform eventually deterministic two-qubit logic 
gates on spatially separated stationary qubits via photon pair measurements. 
Under non-ideal conditions, where photon loss is a possibility, the 
resulting gates can still be used to build graph states for one-way quantum 
computing. In this paper, we describe the RUS method, present possible 
experimental realizations, and analyse the generation of graph states.
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