Tuesday, February 28, 2012

Majorana Fermion detected?

While all eyes are on the LHC to discover new, interesting particles species, condensed matter physicists have been working hard in attempts to detect Majorana fermions and Magnetic Monopoles in solids.  In today's talk at the American Physical Society’s March meeting in Boston, Massachusetts, Leo Kouwenhoven presented findings that Majorana fermions have been detected in an indium antimonide nanowire apparatus.  Indium antimonide nanowires are connected to a circuit with a gold contact at one end and a slice of superconductor at the other, and then exposed to a moderately strong magnetic field. Measurements of the electrical conductance of the nanowires showed a peak at zero voltage that is consistent with the formation of a pair of Majorana particles, one at either end of the region of the nanowire in contact with the superconductor. As a sanity check, the group varied the orientation of the magnetic field and checked that the peak came and went as would be expected for Majorana fermions.

Although other groups have previously reported circumstantial evidence for the appearance of Majorana fermions in solid materials, Jay Sau, a physicist at Harvard University in Cambridge, Massachusetts, who attended Kouwenhoven’s talk, says that this is a direct measurement. “I think this is the most promising-looking experiment yet,” he says. “It would be hard to argue that it’s not Majorana fermions.”

Multiple schemes have been proposed in which Majorana fermions act as the 'bits' in quantum computers, although Sau cautions that it’s not yet clear whether those created by Kouwenhoven will be long-lived enough to be used in that way. 

- Read more at Nature

Friday, February 17, 2012

The 5% Standard Model

As the LHC's Higgs hunt continues, it's worthwhile to reflect on the current state of cutting-edge experimental particle physics, as a whole.  Indeed the Higgs boson is a prediction of the Standard Model of particle physics, but as former CERN theoretical physicist John Ellis admitted, in the range 114-135 GeV the "present electroweak vacuum would be unstable for such a light Higgs in the Standard Model" forcing one to come up with new physics to stabilize it.  By "new", this means physics beyond the Standard Model, such as for example, supersymmetry.  Yet, let's pretend the Standard Model is nice and stable with a ~125 GeV Higgs particle.  Does it tell us about every type of matter in the universe?  Sadly, it doesn't.  Ordinary matter accounts for only 4.6% of the mass-energy content of the observable universe, while mysterious dark matter makes up about 23%.  The rest of the mass-energy content, about 72.4%, is in the form of dark energy.  So cosmologically, the Standard Model doesn't seem so standard after all. 

So what kind of model explains the physics of dark energy and dark matter (the 95.4% of the universe), along with the 4.6% nicely described by the Standard Model?  Many theorists would agree such a model must come from a complete theory of quantum gravity.  The leading contender for such a theory is M-theory, the theory underlying the 10-dimensional string theories and 11-dimensional supergravity.  There also exist other theories, such as Loop Quantum Gravity, which essentially aims to "quantize" space via Wilson loop operators.  Ultimately, the goal is unification of all forces and matter in the universe, using just a single theory.  And this theory, in turn, should describe 100% of the universe.

Are we close to figuring out a complete theory of quantum gravity, hence a theory of all matter and forces?  There are hints that we are, but as always, many hurdles are mathematical.  Historically, Newton had to invent Calculus to describe motion properly.  Einstein had to invoke the tools of Riemann's Differential Geometry to describe space-time curvature.  And will it now be Connes' Noncommutative Geometry that will serve as the magic bullet for quantum gravity?  There is evidence that it might, as the coordinates of branes in string/M-theory are naturally noncommutative.  Erik Verlinde has even proposed a model for dark energy and dark matter, which as a matrix model, is an application of noncommutative geometry.  From a historical perspective, the use of new geometrical mathematics has proven fruitful, so we may very well be on the verge of a new physics revolution.