måndag 8 februari 2010

Spirals and magnetic fields

This is linked to my earlier story http://zone-reflex.blogspot.com/2010/01/spirals-very-small-and-very-big.html

Researchers create 'synthetic magnetic fields' for neutral atoms, an article in Phys.org last dec. An atom can be made to behave as a vortex. Very much in the same way as a soundwave do. You see all the spots. The laser beams, combined with an external magnetic field cause the atoms to "feel" a rotational force; the swirling atoms create vortices in the gas.

Top panel shows time sequence of (a.u., arbitrary units.) Bottom panel shows vortex number Nv (solid symbols) and atom number N (open symbols)from Nature art.

Researchers have created "synthetic" magnetic fields for ultracold gas atoms, in effect "tricking" neutral atoms into acting as if they are electrically charged particles subjected to a real magnetic field. These ultracold gases have become ideal laboratories for studying the complex behavior of material systems. Unlike usual crystalline materials, they are free of obfuscating properties, such as impurity atoms, that exist in normal solids and liquids. However, studying the effects of magnetic fields is problematic because the gases are made of neutral atoms and so do not respond to magnetic fields in the same way as charged particles do. The laser-illuminated neutral atoms react to the varying magnetic field in a way that is mathematically equivalent to the way a charged particle responds to a uniform magnetic field. The neutral atoms experience a force in a direction perpendicular to both their direction of motion and the direction of the magnetic field gradient in the trap. By fooling the atoms in this fashion, the researchers created vortices in which the atoms swirl in whirlpool-like motions in the gas clouds. The vortices are the "smoking gun," Spielman says, for the presence of synthetic magnetic fields.

At a one-vortex-per-atom ratio, they could observe the quantum Hall effect and control it in unprecedented ways. In turn, they hope to coax atoms to behave like a class of quasiparticles known as "non-abelian anyons," a required component of "topological quantum computing," in which anyons dancing in the gas would perform logical operations based on the laws of quantum mechanics.

So also the atom has spirals.

Quantum communication networks show great promise in becoming a highly secure communications system. By carrying information with photons or atoms, which are entangled so that the behavior of one affects the other, the network can easily detect any eavesdropper who tries to tap the system.

So, an atom can be entangled too. Entanglement is not only a quantum property, an uncertainty in a particle. Physicists working up from atoms to Schrodinger's cat. Schrodinger's cat, a macroscopic object that is both alive and dead at the same time, illustrates the strangeness of quantum mechanics. While such quantum properties have been widely observed for electrons and molecules, recent experiments have shown that larger objects may also demonstrate quantum effects. Just how large, though, is still an open question.

Molecules can begin to spiral when they react too.

'Tornadoes' are transferred from light to sodium atoms. Tornado-like rotational motions have been transferred from light to atoms in a controlled way at the National Institute of Standards and Technology. The new quantum physics technique can be used to manipulate Bose-Einstein condensates. As reported in the Oct. 27 2006 issue of Physical Review Letters, the research team transferred orbital angular momentum--essentially the same motion as air molecules in a tornado or a planet revolving around a star--from laser light to sodium atoms.

Physicists have finally managed to demonstrate quantum entanglement of spatially separated electrons in solid state circuitry. For the first time, physicists have convincingly demonstrated that physically separated particles in solid-state devices can be quantum-mechanically entangled. The experiment is reported in an upcoming issue of Physical Review Letters and highlighted with a Viewpoint in the January 11 issue of Physics.

Superposed quantum systems are correlated. And tripartite systems can behave quite surprisingly. A wedding cake is the result :)

Quantum phase transitions also show universal critical behaviors, which are affected not only by temperature but also by quantum mechanics. Also classical phase transitions…often share many fundamental characteristics near the critical point.

The phase transitions are the criticality key?

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