Context, spacetime loops and the interpretation of quantum mechanics
Journal of Physics A: Mathematical and Theoretical 40:12 (2007) 3223-3243
Abstract:
Three postulates are discussed: first that well-defined properties cannot be assigned to an isolated system, second that quantum unitary evolution is atemporal, and third that some physical processes are never reversed. It is argued that these give useful insight into quantum behaviour. The first postulate emphasizes the fundamental role in physics of interactions and correlations, as opposed to internal properties of systems. Statements about physical interactions can only be framed in a context of further interactions. This undermines the possibility of objectivity in physics. However, quantum mechanics retains objectivity through the combination of the second and third postulates. A rule is given for determining the circumstances in which physical evolution is non-unitary. This rule appeals to the absence of spacetime loops in the future evolution of a set of interacting systems. A single universe undergoing non-unitary evolution is a viable interpretation. © 2007 IOP Publishing Ltd.Long-lived mesoscopic entanglement outside the Lamb-Dicke regime
Physical Review Letters 98 (2007) 063603 4pp
How to build a 300 bit, 1 GIGA-operation quantum computer
Quantum Information and Computation 7:3 (2007) 171-183
Abstract:
Experimental methods for laser control of trapped ions have reached su cient maturity that it is possible to set out in detail a design for a large quantum computer based on such methods, without any major omissions or uncertainties. The main features of such a design are given, with a view to identifying areas for study. The machine is based on 13000 ions moved via 20μm vacuum channels around a chip containing 160000 electrodes and associated classical control circuits; 1000 laser beam pairs are used to manipulate the hyperfine states of the ions and drive fluorescence for readout. The computer could run a quantum algorithm requiring 109 logical operations on 300 logical qubits, with a physical gate rate of 1 MHz and a logical gate rate of 8 kHz, using methods for quantum gates that have already been experimentally implemented. Routes for faster operation are discussed. © Rinton Press.A tutorial on quantum error correction
Proceedings of the International School of Physics "Enrico Fermi" 162 (2006) 1-32
Down the information back-alley
Nature Physics Springer Nature 2:12 (2006) 805-806