Antimatter and Quantum Physics

We’re on the Verge of Two World-Changing Antimatter Discoveries

By Alasdair Wilkins, io9.com
While the Large Hadron Collider is looking for the Higgs boson, we're on the verge of two huge antimatter-related breakthroughs. One could finally solve the universe's oldest mystery, while the other could reveal strange new particles that are perfect for quantum computers.

The first result comes from CDF, one of the two long-running experiments at the now deactivated Tevatron accelerator at Fermilab. CDF physicists had been studying the decay of subatomic particles called D-mesons - particles made up of massive charm quarks that form in the decay of even heavier bottom quarks, which in turn decay into kaons and pions.

Late last year, the Large Hadron Collider announced that there was something strange about this decay process. According to our current understanding of physics, the amount of matter and antimatter created in this decay should have been within 0.1% of each other. But the decay actually varied by 0.8%, creating a small but significant imbalance between matter and antimatter that, over the course of the entire history of the universe, could go a long way to explaining why our universe is almost all matter and devoid of antimatter.
The CDF examined the decay process to see how the LHC results stood up. The initial findings had what's known as a 3.5-sigma confidence level, meaning there was a 99.95% chance the results were not somehow a product of random error or statistical fluctuation. That's impressive, but well short of the 5-sigma needed for an official discovery. Well, the CDF found a similar variance in the D-meson decay rate of 0.62% — to the mild surprise of CDF head Giovanni Punzi, who called this a "very unusual result" — and now the phenomenon has reached the 4-sigma confidence level.

It's not an official discovery yet, but it's looking very promising at this stage. The Large Hadron Collider and
Tevatron used very different methods and environment to arrive at strikingly similar and highly unexpected results. Whatever is going on, it definitely can't be ignored — Punzi suggested theoretical physicists will now need to consider whether these results really could presage a new branch of physics, or whether the teams' calculations are somehow wrong.

As Liverpool University physicist Tara Shears told the BBC:
　

"We don't know yet if we are seeing the first signs of new physics, or are starting to understand the Standard Model better. What we've seen is a hint that's worth looking into. And the fact that CDF see the same effect as LHCb is confirmation that this is really worth doing."

The other big antimatter-related result hasn't come from a big particle accelerator but instead a nanowire in a Dutch laboratory. According to a team led by Leo Kouwenhoven of the Delft University of Technology, they have spotted what could be the first experimental evidence of Majorana particles, first proposed by Ettore Majorana over 70 years ago.

These theoretical particles are a unique exception to the standard relationship of matter and antimatter, in that they don't annihilate each other when they come into contact. Majorana realized in 1937 that a fermion with no electric charge would have a completely identical antiparticle, meaning pairs of these particles would be able to exist together without destroying one another. They're remained strictly theoretical until now, when Kouwenhoven reported the first tentative evidence of their existence, as New Scientist reports:
　

Their Majorana particles are not free agents of the sort that might wander into a particle detector on their own, but collective excitations of electrons and "hole" states – absences of electrons – within nanoscale wires made of the semiconductor indium antimonide. Kouwenhoven and his team saw a suggestive blip in the spectrum of energies in the nanowire consistent with the formation of an object of precisely zero energy – exactly the signature that a pair of Majorana fermions would be expected to produce. The clincher came when the team applied a magnetic field to the nanowire. Had the signal come from anything else but a Majorana pair, its energy would have changed in response to the field. But it didn't.

This finding enjoys far less confidence than the d-meson decay, but it could well represent the first sighting of a true Majorana pair. And there's a good practical reason to hope that this result stands up — Majorana particles are pretty much the ideal candidates for qubits, the basic units of quantum computers. While ordinary bits can only perform one calculation at a time, qubits can be put in superpositions that allow many different calculations to be performed simultaneously.

Unlike other qubit candidates like photons or trapped ions, Majorana pairs could be
separated and used to encode the same information at two different sites, making them far more resilient to the random fluctuations of their surroundings. That would solve the fragility problem that remains a major hurdle for quantum computing, and it might well mean that revolutionizing our understanding of physics is just the beginning of what these particles can do.

Via BBC News and New Scientist.
http://io9.com/5889828/were-on-the-verge-of-two-world+changing-antimatter-discoveries