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The December 2005 issue of Nature Physics is available online.

December 2005

Quantum objects trapped on a chip

Single ions — atoms that have gained or lost electrons — emerged recently as candidates for carrying the kind of information needed in a quantum computer. In the January issue of Nature Physics, Christopher Monroe and colleagues report that traps for ions can be hosted on a chip. This could have implications for the construction of powerful systems for quantum information processing.

The team trapped single ions in channels — made from semiconductors — that are narrower than a tenth of a millimetre, and demonstrated that they could be controllably manipulated. This technique could eventually allow higher degrees of control of the ions than in the current devices, and the traps might become the unit cell of a quantum information processor.

The authors make use of a technology called microelectromechanical systems (MEMS) that is already established for the fabrication of micrometre-scale devices. Unlike earlier approaches for constructing ion traps on a chip that require manual assembly, this architecture is in principle suitable for further miniaturization and for linking several traps together.

Ion trap in a semiconductor chip pp 36 - 39

D. Stick, W. K. Hensinger, S. Olmschenk, M. J. Madsen, K. Schwab and C. Monroe

Published online: 11 December 2005 | doi 10.1038/nphys171


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Beat computer viruses with the right connections

Computer viruses pose an ongoing threat and their neutralization calls for new strategies. Reporting in the December issue of Nature Physics, Eran Shir and colleagues propose a solution with a scheme to help an 'antivirus' reach an at-risk computer faster than the virus itself. This approach could mean that computers can be immunized against the spread of infection and that cyber-plagues can be contained.

Current immunization strategies — such as the antiviral software on your PC — are static. But the need to respond to cyber-attacks in real time has spurred efforts to create artificial immune systems that could autonomously identify viruses and develop immunizing agents. In such schemes, the vaccine would spread to other computers in the same epidemic fashion as the virus, but it would reach most computers too late — later than the virus. The team suggest that there is a way to counteract the head start of the virus.

Using network theory — a branch of statistical physics — the authors show that the design of a computer network can be slightly modified to have just a handful of extra connections open only to the vaccine. This is enough to enable the vaccine to outrun the virus and spread to other computers, immunizing them before the virus gets there, and preventing a cyber-plague.

Distributive immunization of networks against viruses using the 'honey-pot' architecture pp 184 - 188

Jacob Goldenberg, Yuval Shavitt, Eran Shir and Sorin Solomon

Published online: 1 December 2005 | doi 10.1038/nphys177


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Blowing bubbles like clockwork

A remarkable example of self-organised complexity in a rudimentary microfluidic bubble generator is described in the December issue of Nature Physics. The generator not only produces intricately complex patterns of bubbles, but repeats these patterns over and over with astonishing fidelity, as if by clockwork. Yet their generator is decidedly not clock-like, consisting of a simple network of fewer than a dozen microfluidic channels. The emergence of self-organized complexity in so simple a system provides a promising avenue for better understanding the origin of chaotic and complex behaviour.

The study of complexity informs our understanding of many physical and social phenomena, from the formation of hurricanes to the fluctuation of stock markets. But because of the inherent sensitivity of most complex systems to small changes in any of the multitude of parameters that influence their behaviour, getting a complete picture of the mechanisms that govern complexity in the real world is close to impossible.

The authors' device consists of a simple array of microfluidic channels that convey water into a central channel into which air is fed. The bubbles that emerge at the end of this channel form a variety of difference types of patterns from completely regular to completely chaotic, depending on the pressure of the air and water fed into the system. In one particular regime of operation, the system generates a long sequence of bubbles of differing size and distribution in the output channel that repeats almost exactly — in both space and time — up to 100 times or more. By systematically varying the parameters of their device, such as the size and shape of its channels, the authors hope in future to better understand how such behaviour can emerge in the absence of complex external influences.

Oscillations with uniquely long periods in a microfluidic bubble generator pp 168 - 171

Piotr Garstecki, Michael J. Fuerstman and George M. Whitesides

Published online: 1 December 2005 | doi 10.1038/nphys176


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