Saturday, July 18, 2009

Topological Insulators

Edge-State Physics Without Magnetic Fields in Science.
Solids can be divided into conductors and insulators. A new class of materials, called topological insulators, has been predicted (1, 2) that exhibit surface states that lead to quantized conductance of charge and spin. These surface states are helical edge states, which interconnect spin and momentum of the carriers. Observation of these states should not require application of a magnetic field.

Here's a potential application: Topological Quantum Image Analysis physics preprint.
A new approach to analyzing visual images is proposed, based on the idea of converting an optical image into a spatially varying pattern of polarized squeezed light, which is then used to produce a pattern of chiral edge currents in a thin film topological insulator. Thin films of Bi or Bi doped with Sb which are punctured with an array of sub-micron holes may be a way of realizing this kind of optical quantum information processing.

For a good introduction see A New Spin on the Insulating State in Science.

A Deeper Quantum Theory?

Is Quantum Theory Exact? by Stephen L. Adler and Angelo Bassi.
According to the standard theory, the state of a quantum system evolves deterministically according to Schrödinger's equation until the state is measured, when there's an apparently instantaneous nondeterministic transition to a new state.
How can we reconcile this probabilistic distribution of outcomes with the deterministic form of Schrödinger's equation? What precisely constitutes a "measurement?" At what point do superpositions break down, and definite outcomes appear? Is there a quantitative criterion, such as size of the measuring apparatus, governing the transition from coherent superpositions to definite outcomes? These puzzles have inspired a large literature in physics and philosophy.

The article asks whether there might be a deeper-level theory which explains quantum weirdness.
See also their preprint Collapse models with non-white noises.

Cats Modify Purring to Manipulate their Owners

Cat Purrs Evoke Baby Cries
There may be more to a cat's purr than meets the ear. A new study reports that our feline friends modify their signature sound when seeking food, adding a higher-frequency element that exploits our sensitivity to infant wails--and thus making it harder to ignore.

Elegant Microfluidic Images

This article contains more nice photomicrographs of emulsions High-Order Multiple Emulsions Formed in Poly(dimethylsiloxane) Microfluidics.

Climate Flip-Flops

What Drives Climate Flip-Flops?
Around 14,600 years ago, the atmospheric circulation over the North Atlantic region flipped within just a few years to another state (2); also, Greenland temperatures skyrocketed by >10°C over several decades (3), terminating a cold phase known as Heinrich Event 1. The global impacts of this Bølling-Allerød transition have been well documented with climate proxy records such as sediment cores and ice cores, but the physical conditions that triggered the transition remain controversial. The temperature evolution from the Heinrich Event 1 to the Bølling-Allerød and the subsequent Younger Dryas cold phase (see the figure) is strikingly similar to the Dansgaard-Oeschger cycles (4) that dominated Northern Hemispheric climate between 60,000 and 30,000 years ago (5). Hence, unraveling the processes that triggered the Bølling-Allerød transition may also help to elucidate the mysterious, tantalizingly regular Dansgaard-Oeschger cycles (6).

Giant Planets on the Move!

Shifting Orbits Gave Solar System A Big Shakeup, Model Suggests
Planetary scientists are finding that the four outermost planets of our solar system haven't always been orbiting where they are today. They've moved, some a considerable distance outward. The most catastrophic scenario for such planet migration, dubbed the Nice model (after the French city), has been gaining ground of late. It envisions the great reshuffling as a brief, violent affair that not only put the outer planets where they are today but also created the Kuiper belt of small icy bodies beyond Neptune, gave the planets scores of oddly orbiting moons, and bombarded the solar system with a rain of asteroids and comets so fierce that it would have cooked all but the deepest subterranean life on early Earth. The latest support for the Nice model, a new explanation for primitive-looking asteroids, appears this week in Nature. But the model has more hurdles to clear, such as explaining why the innermost planets—Earth and its neighbors—weren't reshuffled as well.

Mysterious Ancient Global Warming

Ancient Climate-Change Event Puzzles Scientists
Over the past couple of decades, researchers have been gathering data about a mysterious event known as the Paleocene-Eocene Thermal Maximum (PETM). The data, derived from drill cores brought up from the deep seabed in the Atlantic and Pacific Oceans, show that the surface temperature of the planet rose by as much as 9°C within 10,000 years during the PETM, which itself started out warmer than our current world. Temperatures stayed at this elevated level for nearly 100,000 years.